Application of Starch

#### Chapter 4

## Studies on the Property and Application of Starch Sugar Ester Dodecenylsuccinic

Liu Zhongdong, Liu Boxiang, Wei Guohua, Zhu Xin and Wang Huabin

#### Abstract

In this study, we have prepared starch and Brown algae sugar ester dodecenylsuccinic, and by using infrared rays, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC), we studied the structures and properties of the starch and Brown algae sugar ester dodecenylsuccinic. In addition, we studied the possibility of using this modified starch and Brown algae as emulsifier that can be used in ice cream.

Keywords: starch sugar ester dodecenylsuccinic (Brown algae sugar modified), property and application

#### 1. Introduction

Starch sugar ester is one kind of starch derivatives and it is obtained by modifying starch via former liquefying, then esterifying or by former esterifying, then liquefying. It is an important kind of safe additive, which possessed good emulsification and dense increasing abilities, and is degradable. Starch sugar ester has been an important modified starch in food industry [1–3]. Starch sugar ester, in particular, has been used to stabilize flavor concentrates in beverages, oil in salad oil, and to encapsulate flavors, fragrances, and vitamins. Also it can be used in meat foods, cooking foods, cheese, etc. Starch sugar ester has also important application in papermaking industry, medicine industry, petroleum and chemical industry, etc. With the incorporation of alkenylsuccinates groups into normally starch molecules, starch sugar ester obtains hydrophobic and hydrophilic properties. After liquefaction, we can get starch products of different dense and mobile properties. Starch sugar ester, particularly starch sugar ester dodecenylsuccinate, has some good properties, which other products do not have, and its dense and emulsification abilities are specific [4].

#### 2. Experimental

#### 2.1 Materials

The materials used were as follows: wheat starch (Anyang Hei Tai Limited Liability Company of wheat starch), alkenylsuccinate

(LvShun Chemical Factory have purified by distillation), Termamyl®120L, Types (Novo, Inc.).

#### 2.2 Reagents and instrument

Acetone, hydrochloric acid, NaOH, DMSO, LD4-2 centrifuge (Beijing Centrifuge Factory), JJ-1 Mixer (Shenzhen GUOHUA Instruments Factory), PHS-3C pH meter (Shanghai Leici Instrument Factory), Spray dried Meter (NIRO, Danman), Model 1000B Scanning electron microscopy (AMYRAY, America), Differential Scanning (Calorimetrg-2C, PE, America), PERKIN-ENMER 983G Infrared Rays Merer (PE, America).

#### 2.3 Preparation of wheat starch sugar ester dodecenylsuccinic

#### 2.3.1 The first method

#### 2.3.1.1 Preparation of wheat starch dodecenylsuccinic

Starch was agitated in deionized water with vigorous stirring. The pH was maintained between 8.0 and 9.0 using a 4% NaOH solution. Dodecenylsuccinic anhydride was added slowly, the reaction was allowed to proceed for several hours, then adjusted to 7.0 using HCl, the slurry was filtered, washing with deionized water three times, then washing with acetone one time, centrifuging the isolated insoluble product was air-dried.

#### 2.3.1.2 Liquefaction of wheat starch dodecenylsuccinic

Wheat starch dodecenylsuccinate was slurried with deionized water. The pH was regulated to 5.7; Termamyl®120L, Type S was added with stirring and made to react for some time, and then, the slurry was dried by spray.

#### 2.3.2 The second method

Wheat starch was agitated in deionized water to consistency of 35%. The pH was regulated to 5.7; Termamyl®120L, Type S was added with stirring, and reacting it for 50 min at 85°C killed enzymes. Then, the pH was maintained between 8.0 and 9.0; dodecenylsuccinic anhydride was added slowly, reaction for several hours, then adjusted to 7.0 using HCl, the slurry was filtered, washing with deionized water three times, washing with acetone one times, centrifuging the isolated product was dried by spray.

#### 2.4 The properties analysis of products

#### 2.4.1 Scanning electron microscopy

Scanning electron microscopy measurements were carried out by the procedure of Shiying [5].

#### 2.4.2 Infrared rays

The products was mixed with KBr, pressed to slice, and then determined with Perkin-Elmer 983G Infrared Rays Meter [6].

Studies on the Property and Application of Starch Sugar Ester Dodecenylsuccinic DOI: http://dx.doi.org/10.5772/intechopen.89744

#### 2.4.3 Different scanning calorimetry (DSC)

Samples (about 5 mg) were weighed directly into previously weighed aluminum DSC pans (Table 1). Water was added to obtain the starch-water ratio of 1:1, and the pans were sealed. An empty pan was used as reference. The scanning rate was 2 deg/min. The scanning range was between 320 and 470 k; Means and standard deviations were calculated.

#### 2.4.4 The analysis of the abilities of water-holding and the stability of thawing-melting

Dry starch (1 g) was agitated in deionized water (49 g), heated to boil, cooled to room temperature, centrifuged for 10 min (3000 r/min), then the volume of upper part was determined (V1), the lower part for 24 h (�18°C) was frozen, then thawed, centrifuged for 10 min (3000 r/min), determining the volume of upper part (V2) [7].

$$\text{the ability of water} - \text{hading} = \frac{50 - \text{V}\_1 - \text{V}\_2}{\text{weight of starch}}$$

$$\text{the resistment of thawing} - \text{melling} = \frac{1}{\text{V}\_2}$$

Thawing-melting cycle and water-holding capacity are shown in Table 2.

#### 2.4.5 Degree of substitution (DS) determination

A known weight of the sample was dissolved in 10 ml of DMSO by heating (70°C, 10 min) [8]. After cooling, 5–6 drops of phenolphthalein in dictator were added. This solution was titrated against 0.05 M standard NaOH solutions until a permanent pale pink color was seen. The DS was calculated by using the following equation:

$$DS = \frac{0.162A}{1 - 0.2664A}$$

where A is the millimolarity of the NaOH solution in which 1 g sample is reacted. A is calculated as follows:

$$\mathbf{A} = \frac{V \times M}{m}$$


Table 1.

DSC parameters for native and modified starches.


#### Table 2.

Thawing-melting cycle and water-holding capacity.

where V is the volume of NaOH solution used during titration, M is the molarity of the NaOH solution, and m is the weight of sample analyzed.

#### 2.5 The preparation of ice cream in which the modified starch is used as emulsifier

#### 2.5.1 The rate of ice-cream expanding

#### 2.5.2 Determination of the resistance of ice-cream melting

The ice cream was cut to a block (about 100 g) at room temperature (27°C), and then it was put in the sieve and the time of the first drop dripped was recorded [9].

#### 3. Result and discussion

#### 3.1 Scanning electron microscopy

Figure 1 shows the wheat starch ester dodecenylsuccinate of the first method (1#: Unmodified wheat starch, 2# DS = 0.0073, 3#DS = 0.0102, 4#DS = 0.0150, 5# DE = 4.5, 6# DE = 6.9); wheat starch ester dodecenylsuccinate of the second method (7#DE = 8.2, 8# DE = 9.7, 9# DE = 11.6); and wheat starch ester dodecenylsuccinate of the second method (10# DS = 0.0099, 11# DS = 0.0112, 12# DS = 0.0146).

The unmodified starch granules have an oval or round pattern. For the DS of products, (2#) is low. We only saw individual granules surface were corroded. With the rising of DS, the number of starch granules corroded rises and forms some holes Studies on the Property and Application of Starch Sugar Ester Dodecenylsuccinic DOI: http://dx.doi.org/10.5772/intechopen.89744

Figure 1. SEM images of different starch.

(3# and 4#). This shows that the reaction is at the granule surface first. From the images of 5#, 6#, 7#, 8#, and 9#, we can see the obvious holes, which indicate that it is feasible and that we liquefied starch granules with α-amylase. Either liquefaction former or latter, the starch granules all maintaining granule pattern liquefaction first can increase the reaction area on starch granules surface.

#### 3.2 The infrared ray analysis of different products

Figure 2 shows the analysis of the different products, where 1#: unmodified wheat starch; 2#: wheat starch sugar ester dodecenylsuccinate of the first method (DS = 0.0150); 3#: wheat starch sugar ester dodecenylsuccinate of the first method (DE = 6.3); and 4#: wheat starch sugar ester dodecenylsuccinate of the second method (DS = 0.0146).

In Figure 2, the absorptions of 1737 cm<sup>1</sup> of 2#, 1738 cm<sup>1</sup> of 3#, 1739 cm<sup>1</sup> of 4# are the absorptions γc=0—the character of ester, the absorptions of diene bond (C=C–C=C). From the analysis of the ester bond and diene bond and the comparison the spectrums unmodified wheat starch, it was proved that the products have been estered.

#### 3.3 The differential scanning calorimetric analysis of different products

1#: unmodified wheat starch, wheat starch esterdodecenylsuccinate of the first method (2# DS = 0.0073, 3#DS = 0.0150, 4# DS = 0.0121, 5# DE = 6.3). Wheat

Figure 2. Infrared rays thermograms of the different products.

Studies on the Property and Application of Starch Sugar Ester Dodecenylsuccinic DOI: http://dx.doi.org/10.5772/intechopen.89744

starch ester dodecenylsuccinate of the second method (6# DE = 0.0107, 7# DS = 0.0146).

Compared with unmodified wheat starch, the different phases temperature of starch sugar ester descend, and they have low gelatinization enthalpy. This shows that after the alkenylsuccinate group was lead into the starch molecule, it could block hydrogen bond to form between starch chains, decreasing the bonding power away the molecule and making the structure of starch granule to become limp. Crystallized region becomes smaller, which shortens the procedure of gelatinization, and it needs less heat quantity. The reason of absorbing enthalpy of 5# may be the high DE value. The action of α-amylase was found not only in the amorphous region of starch granule but also in the region of crystallization. Also it may be eroded the molecule chain of the starch granule and easy to be melted, so the absorbing enthalpy becomes small.

#### 3.4 Determination of the abilities of water-holding and the stability of thawing-melting

Using the first method, the starch ester dodecenylsuccinic has better waterholding ability and antifreeze capacity than the unmodified starch. From the date of 2#, 3#, and 4#, we found that the low degree of substitution of starch ester dodecenylsuccinic is better than the high one in the stability of thawing-melting. The unfrozen paste of unmodified starch separated out lots of water, the paste was white and muddy, elasticity and became fragment after stirring. We did the same action to the starch ester dodecenylsuccinic and found that the paste can hold transparent gel, in which the elasticity and the frame structure were good. The change was neglectable between after freezing and before freezing. Using the first method, the starch sugar ester dodecenylsuccinic had better water-holding ability than the unmodified wheat starch and wheat starch ester dodecenylsuccinic. The stability of thawing-melting was similar between the two methods of starch sugar ester dodecenylsuccinic.

#### 3.5 Approachment of the application of starch sugar ester which is used as emulsifier in ice cream

#### 3.5.1 Directions for producing ice cream and emulsifier

Directions for producing ice cream are shown in Table 3 and directions for producing emulsifier are shown in Table 4.


Table 3. Composition of ice-cream.


#### Table 4.

Types and mass of emulsifier.

#### 3.5.2 Determination of the expanding rate of ice cream

The results of expanding rate of ice cream are shown in Figure 3.

Compared with the ice cream without emulsifier, the expanding rate increased after using starch sugar ester as emulsifier. After using the mixture of starch sugar ester, glycerol monostearate and sucrose ester, the expanding rate of ice cream increased a lot. This showed that the starch sugar ester mixture, glycerol monostearate and sucrose ester, has a cooperative effect.

#### 3.5.3 Determination of melting rate of ice cream

The results of melting rate of ice cream are shown in Figure 4.

From Figure 4, we find that using starch sugar ester as emulsifier, the melting rate of ice cream can increase 12%, compared with glycerol monostearate and

Studies on the Property and Application of Starch Sugar Ester Dodecenylsuccinic DOI: http://dx.doi.org/10.5772/intechopen.89744

Figure 4. Melting rate of ice cream.

sucrose ester. Also using the mixture of starch sugar ester, glycerol monostearate and sucrose ester, the melting rate of ice cream can increase 8%.

#### 4. Conclusions


#### Acknowledgements

This work was supported by National Natural Science Foundation of China Grant No. 30270762. We thank National Natural Science Foundation Committee for financial support.

Chemical Properties of Starch

### Author details

Liu Zhongdong, Liu Boxiang\*, Wei Guohua, Zhu Xin and Wang Huabin Henan University of Technology, Zhengzhou, P.R. China

\*Address all correspondence to: jollier.liu@gmail.com

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Studies on the Property and Application of Starch Sugar Ester Dodecenylsuccinic DOI: http://dx.doi.org/10.5772/intechopen.89744

#### References

[1] Ntawukulilyayo JD, Desmedt S-C, Demeester J, et al. Stabilization of suspensions using sucrose esters and low substituted noctenylsuccinate starch xanthan gum associations. International Journal of Pharmaceutics. 1996;128 (1–2):73-79

[2] Trubiano PC. The role of specialty food starches in flavor encapsulation. ACS Symposium Series. 1995;610: 244-253

[3] Tsubomoto H, Matsubara I. Starch containing octenyl succinate as additive to cheese. Japanese Kokai Tokkyo Koho. JP111-69,072[99169,072]

[4] Jiancheng L, Changgui Y. Starch sugar ester—A new food emulsifier. China Food Additives. 2001;3:26-29

[5] Shiying Z, Chuntao Z. Study on edible phosphate monoester starch. Journal of Wuxi University of Light Industry. 1989;8(4):7-14

[6] Aburto J, Alric I, et al. Properties of long-chain esters of starch using fatty acid chlorides in the absence of an organic solvent. Starch-Starke. 1999;51: 132-135

[7] Lisheng F. Study on properties of sweet potato starch. Grain and Fodder Industry. 2001;2:49-51

[8] Jeon Y-S, Viswanathan A, Gross RA. Studies of starch esterification: Reactions with alkenyl succinates in aqueous slurry systems. Starch-Starke. 1999;51:90-93

[9] State Standard of China/T 10009-1998. Test Methods for Frozen Food

#### Chapter 5

## Chemical Properties of Starch and Its Application in the Food Industry

Henry Omoregie Egharevba

#### Abstract

Starch is an important food product and a versatile biomaterial used world-wide for different purposes in many industrial sectors including foods, health, textile, chemical and engineering sector. Starch versatility in industrial applications is largely defined by its physicochemical properties and functionality. Starch in its native form has limited functionality and application. But advancements in biotechnology and chemical technological have led to wide-range modification of starch for different purposes. The objective of this chapter is to examine the different chemical reactions of starch and expose the food applications of the modification products. Several literatures on starch and reaction chemistry including online journals and books were analyzed, harmonized and rationalized. The reactions and mechanisms presented are explained based on the principles of reaction chemistry. Chemical modification of starch is based on the chemical reactivity of the constituent glucose monomers which are polyhydroxyl and can undergo several reactions. Starch can undergo reactions such as hydrolysis, esterification, etherification and oxidation. These reactions give modified starches which can be used in baked foods, confectionaries, soups and salad dressings. This chapter discusses the different chemical reactions of starch, the associated changes in functionality, as well as the applications of chemically modified starches in the food industry.

Keywords: reactions of starch, hydrolysis, esterification, etherification, baked products, confectioneries, gravies, soups and sauces, mayonnaises and salad dressing

#### 1. Introduction

Starch also known as amylum, is an important food product and biomaterial used world-wide for different purposes. Though traditionally used in the food industry, technological advancement has led to its steady relevance in many other sectors such as health and medicine, textile, paper, fine chemicals, petroleum engineering, agriculture, and construction engineering [1]. It is used in the food industry either as food products or additives for thickening, preservation and quality enhancer in baked foods, confectioneries, pastas, soups and sauces, and mayonnaises. Starch is a polysaccharide of glucose made of two types of α-D-glucan chains, amylose and amylopectin. Starch molecules produced by each plant species have specific structures and compositions (such as length of glucose chains or the

amylose/amylopectin ratio), and the protein and fat content of the storage organs may vary significantly. Therefore, starch differs depending on the source. This inherent functional diversity due to the different biological sources enlarges its range of industrial uses [2, 3].

The structural and compositional differences in starches from different sources determine its properties and mode of interactions with other constituents of foods that gives the final product the desired taste and texture. In the food industry, starch can be used as a food additive to control the uniformity, stability and texture of soups and sauces, to resist the gel breakdown during processing and to raise the shelf life of products [2]. Starch is relatively easily extractable and does not require complicated purification processes. It is considered to be available in large quantities in major plant sources such as cereal grains and tubers. These sources are generally considered inexpensive and affordable and serve as raw materials for commercial production [4].

Starch from Zea mays (corn, Figure 1) account for 80% of the world market production of starch. Maize starch is an important ingredient in the production of many food products, and has been widely used as a thickener, stabiliser, colloidal gelling agent, water retention agent and as an adhesive due to its very adaptive physicochemical characteristics [5]. Starches from tubers of roots such as potato tubers (Figure 1), which are considered non-conventional sources have found usefulness in providing options for extending the spectrum of desired functional properties, which are needed for added-value food product development.

The stability of native starch under different pH values and temperatures varies unfavorably. For instance, native starch granule is insoluble in water at room temperature and extremely resistant to hydrolysis by amylase. Hence native starch has limited functionality. In order to enhance properties and functionality such as solubility, texture, viscosity and thermal stability, which are necessary for the desired product or role in the industry, native starches are modified. The widening vista of application possibilities of starches with different properties has made research in non-conventional starches and other native starches more imperative [2, 6, 7]. Recent studies on the relationship between the structural characteristics and functional properties of starches from different sources have continued to provide important information for optimizing industrial applications.

Modification has been achieved mostly by physical and chemical means. Enzymic and genetic modifications are biotechnological processes which are increasingly being explored [8]. While physical modification methods seemed simple and cheap, such as superheating, dry heating, osmotic pressure treatment, multiple deep freezing and thawing, instantaneous controlled pressure-drop process, stirring ball milling, vacuum ball milling, pulsed electric fields treatment, corona electrical discharges, etc., chemical modification involves the introduction of new functional moieties into the starch molecule via its hydroxyl groups, resulting in marked

Figure 1. Corn (A) and potato tuber (B) [2].

Chemical Properties of Starch and Its Application in the Food Industry DOI: http://dx.doi.org/10.5772/intechopen.87777

change in its physicochemical characteristic. The functional characteristics of chemically modified starch depends on a number of factors including the botanic origin of the native starch, reagent used, concentration of reagent, pH, reaction time, the presence of catalyst, type of substituent, degree of substitution, and the distribution of the substituents in the modified starch molecule. Modification is generally achieved through chemical derivatization, such as etherification, esterification, acetylation, cationization, oxidation, hydrolysis, and cross-linking [7]. This chapter discusses the chemical properties of starch and how they determine its application in the food industry.

#### 2. Amylose and amylopectin

The chemical behaviour of starch is dependent on the nature of its constituent compounds. Starch is a homopolysaccharides made up of glucose units. However, the homopolysaccharide are of two types namely: amylose, which is a linear chain consisting of about 500–2000 glucose units, and amylopectin, which is highly branched and consist of over 1,000,000 glucose units. The two types of homopolysaccharides constitute approximately 98–99% of the dry weight of starch [2]. The ratio of the two polysaccharides usually varies depending on the botanical origin of the starch. Botanic source reports that starch chain generally consist of 20% amylose and up to 80% amylopectin by mass. It is believed that starch with up to 80% amylose can exist [7]. Some classification categorize starch containing <15% amylose as 'waxy', 20–35% as 'normal' and greater ≥40% as 'high' amylose starches [9].

Amylose and amylopectin have different physiochemical properties which impact on the overall properties of the starch. Hence it is often important to determine the concentration of each individual component of the starch, as well as the overall starch concentration [10]. The physicochemical (e.g., gelatinization and retrogradation) and functional (e.g., solubility, swelling, water absorption, syneresis and rheological behaviour of gels) properties determine the potential uses of starches in the food industry. These properties depend on the molecular and structural composition of amylose and amylopectin, percent composition and arrangement of these two homopolysaccharides in starch granules which often determine the granule size and shape depending on other genetic factors as a result of the particular species of plant [2].

In food products, the functional roles of starch could be as a thickener, binding agent, emulsifier, clouding agent or gelling agent. In the food industry, native starch is usually reprocessed and modified through chemical processes to improve its functionality for the desired purpose. Chemical modification involves the introduction of new functional groups into the starch molecule which produces in a modified starch with markedly altered physicochemical properties. Such modified starch shows profound change in functionality such as solubility, gelatinization, pasting and retrogradation [11].

The chemical reactivity of starch is dependent on the reactivity of the constituent glucose units [11]. The chemical and functional properties achieved following such modification depends largely on the reaction conditions such as modifying reagent(s), concentration of the reactants, reaction time, type of catalyst used, pH, and temperature. The type of substituents, degree of substitution and distribution of substituents in the starch molecule affects the functional properties.

#### 2.1 Amylose

Amylose is a linear polymer of α-D-glucose units linked by α-1,4 glycosidic bonds (Figure 2). The linear nature of amylose chain and its percentage content in starch,

Figure 2. Chemical structure of amylopectin chain and amylose chain.

and the relative molecular arrangement with amylopectin affect the overall functionality of the starch. Hence starch varies greatly in form and functionality between and within botanical species and even from the same plant cultivar grown under different conditions. This variability provides starches of different properties, which can create challenges of raw materials inconsistency during processing [12].

#### 2.2 Amylopectin

Amylopectin is a branched polymer of α-D-glucose units linked by α-1,4 and α-1,6 glycosidic bonds (Figure 2). The α-1,6 glycosidic linkages occurs at the branching point while the linear portions within a branch are linked by α-1,4 glycosidic bonds. In comparison to amylose, amylopectin is a much larger molecule with a higher molecular weight and a heavily branched structure built from about 95% (α-1,4) and 5% (α-1,6) linkages. Amylopectin unit chains are relatively short with a broad distribution profile, compared to amylose molecules. They are typically, 18–25 units long on average [13, 14].

#### 3. Physicochemical properties of starch

Physical properties are those properties exhibited without any change in chemical characteristics of starch and do not involve the breaking and creation of chemical bonds such as solubility, gelatinization, retrogradation, glass transition, etc. On the other hand, chemical properties changes due to chemical reactions and usually involve the breakage and creation of new bonds. Examples of such chemical processes in starch include hydrolysis, oxidation, esterification and etherification. Research strongly indicates that the molecular weight and branching attributes of starch which play important roles in the shape and size of granules can potentially be used for predicting some of its functionality such as texture, pasting, retrogradation, etc. [12, 15]. Amylose has more proportional relationships with pasting and gel textural properties, while amylopectin which are predominant in regular and waxy corn starches, has higher proportional relationship with firmness.

#### 3.1 Solubility and gelatinization

When unprocessed or native starch granules which are relatively inert are heated in the presence of adequate water, usually during industrial processes, swelling of the

#### Chemical Properties of Starch and Its Application in the Food Industry DOI: http://dx.doi.org/10.5772/intechopen.87777

granules occur and the amylose dissolves and diffuses out of the swollen granules which upon cooling forms a homogenous gel phase of amylose-amylopectin. The swollen amylopectin-enriched granules aggregate into gel particles, generating a viscous solution. This two-phase structure, called starch paste, is desirable for many food applications where processed starches are used as thickeners or binders [2, 16].

#### 3.2 Retrogradation and shear

Retrogradation of starch is a phenomenon that occurs when the disordered arrangement of the polymer molecules of gelatinized starch begins to re-align into an ordered structure in the food product [15]. Preventing retrogradation affects the freeze-thaw stability and textural characteristics and helps to elongate the shelf life of the food product. Starch modification through chemical means, such as, hydrolysis and esterification are generally used to produce starches that can withstand retrogradation. Preventing retrogradation of starch is important for starch used in frozen foods because it is accelerated at cold temperatures, producing an opaque, crystallized, coarse texture as a result of the separation of the liquid from the gel or syneresis [17, 18]. Crosslinked oxidized starches have been reported be more stable against retrogradation [15].

Amylose linear chain dissolves in water at 120–150°C and is characterized by high thermostability, resistance to amylase, high crystallinity and high susceptibility to retrogradation. Amylopectin, which is the branched chain is however, slow to retrogradation, with crystalline forms appearing only on the outside of the globule and characterized by a significantly lower re-pasting temperature of 40–70°C and an increased susceptibility to amylases activity than amylose. Retrogradation of starch is affected botanical origin of the starch, amylose content, length of the amylopectin chains, density of the paste, paste storage conditions, physical or chemical modifications and the presence of other compounds. Recrystallization of starch applies only to amylose chains, and it occurs most readily at temperatures around 0°C, and also at temperatures above 100°C [8]. Physical modification process such as repeated freezing and thawing of the starch paste aggravate retrogradation. The resulting starch thus produced is resistant starch that exhibit resistance to digestibility by amylase enzymes and can be used as an alternative nutrient source for diabetic patients and as a rate controlling polymer coat in controlled drug delivery systems [8].

Starch granules swollen with water are predisposed to fragmentation if exposed to physical severe pressure change. This becomes of major concern where the integrity of the granules is required to maintain viscosity. Shear is the disintegration phenomenon of swollen starch granules or gel. Starch shear arises from the shear stress which builds up during the process of retrogradation and/or gel drying of the gelatinized starch [19]. The stress acting in opposite directions creates a fault-line that causes the material to open up or tear apart. Shearing generally depends on the fluid (gel) viscosity and flow velocity [20]. Starch granules in their raw unswollen forms are not susceptible to damage by shear even in the slurry before cooking. But once cooked or gelatinized, starch granules becomes susceptible to shear, resulting in loss of viscosity and textural stability [19].

#### 4. Chemical properties of starch

The chemical properties of starch are dependent on the reactivity of starch which is a function of the polyhydroxyl functional groups in the constituent glucose monomers. The hydroxyl groups at position C-2, C-3 and C-6 which are free from the glycosidic

bond linkages and pyranose ring formation, are usually free for substitution reactions involving either the attached hydrogen or the entire hydroxyl group. While the ▬OH at C-6 is a primary alcoholic hydroxyl group, those at C-2 and C-3 are secondary alcoholic hydroxyl group. Hence starch can undergo hydrolytic cleavage of its chains at the glycosidic bonds; oxidative reaction with the ▬OH or C▬C bond creating carbonyl groups; and other reactions with various functional and multifunctional reagents to produce esterified and etherified starches. Most of the reactions require activation of the hydroxyl of glucose units in acidic or basic media [7].

#### 4.1 Reactions of starch

The reactivity of starch is dependent on the hydroxyl functions of the constituent α-D-glucan polymers (Figure 2). Thus starch is able to undergo the following reactions.

#### 4.1.1 Hydrolysis

Hydrolysis is an addition reaction and simply involves the addition of a water molecule across a bond resulting in the cleavage of that bond and formation of the cleavage products, usually with hydroxyl group or alcohol functionality. Hydrolysis of starch can be achieved by chemical or enzymatic process. Chemical process of hydrolysis usually employs heating starch in the presence of water or dilute hydrochloric acid (Figure 3). Hydrolysis is also used to remove fatty substances associated with native starches. Hydrolysis under acidic condition is called roasting, resulting in acid modified starch. Treatment of starch with sodium or potassium hydroxide results in alkaline modified starch. Hot aqueous alkaline solutions can be used, and this improves the reducing value of that starch [21–23].

The products of starch hydrolysis include dextrin or maltodextrin, maltose and glucose. Dextrins are mixtures of polymers of D-glucose units linked by α-(1 ! 4) or α-(1 ! 6) glycosidic bonds. The percentage of products obtained depends on the conditions used for the reaction such as duration and strength/amount of reagents used. Enzymic hydrolysis uses the enzyme malto-amylase to achieve hydrolysis and this is the process that usually occurs in starch digestion in the gastrointestinal tract [9]. Dextrins are white, yellow, or brown water-soluble powder which yield optically active solutions of low viscosity. Most of them can be detected with iodine solution, giving a red coloration. White and yellow dextrins from starch roasted with little or no acid are called British gum. The properties of dextrinized starch is dependent upon the reaction conditions (moisture, temperature, pH, reaction time) and the products characteristics vary in its content of reducing sugar, cold water solubility, viscosity, color and stability.

Hydrolytic processes have been used in the food industry to produce starch derivatives with better functional properties and processing applications [2]. Acid and alkali steeping are the two most widely used methods for starch isolation in the

Figure 3. Hydrolysis of α(1 ! 4) glycosidic bond.

Chemical Properties of Starch and Its Application in the Food Industry DOI: http://dx.doi.org/10.5772/intechopen.87777

#### Figure 4.

Esterification reaction of carboxylic acids and alcohols.

food industry, with numerous modifications. Thermo-alkali isolation method known as nixtamalization has been used in Central America since pre-Hispanic times. Acid and alkali isolation processes affect the amylose/amylopectin, protein and lipid content as well as the granule size and shape of the final product [23].

#### 4.1.2 Esterification reaction

The condensation of an alcohol and carboxylic acid usually under acidic condition, to produce an ester and water, is called esterification [24]. Basically, the reaction is between the carboxylic acid group and the alcohol group with the elimination of a water molecule (Figure 4). When the acid anhydride is used, an alkaline condition is preferred in the reaction.

The reaction is usually reversible and the forward reaction is favoured under low pH and excess of alcohol while the reverse is favoured under high pH. Remover of one of the product during the reaction will also favour the forward reaction.

For starch, the reaction is between the carboxylic acid group (▬COOH) of fatty acids or ▬COCl of fatty acid chlorides and the alcohol group (▬OH) of the glucose units. Esterification is generally used to introduce more lipophilic groups into the starch molecule making it more lipophilic and for producing crosslink starch when polyfunctional compounds or multifunctional or reagents capable of esterification or etherification are used [15]. Esterification weakens the inter-molecular bonding that holds the granules together and hence alter the granule shape and sizes as well as other functional properties of the starch. The degree of substitution (DS) is dependent on the concentration of reagent used, the type of reagent used, the catalyst and the duration of reaction [25].

#### 4.1.2.1 Acetylation of starch

Starch can be acetylated by reacting it with acetic anhydride to produce acetylated starch (Figure 5). The hydroxyl group of the glucose units are esterified with the acetyl groups from the acetic anhydride to give starch with glucose units with acetate function. The DS of the hydroxyl group with acetate group is dependent on the reaction conditions. Acetylated corn starch of DS 0.05, 0.07 and 0.08 have been obtained using 4, 6 and 8% (starch d.w.) acetic anhydride respectively and aqueous sodium hydroxide as catalyst [25].

The introduction of the more bulky acetyl group compares with hydroxyl group causes steric hindrance to the alignment of the linear chains. This allows for easy water percolation between chains thus increasing the granule swelling power and solubility resulting in lower gelatinization temperature [25]. The steric hindrance of

Figure 5. Acetylation of starch with acetic anhydride.

#### Chemical Properties of Starch

less polar acetyl group also reduces the amount of inter-molecular hydrogen bond formation, and weakens the granule structure, preventing molecular re-association and realignment required for retrogradation. However, depending on the DS and the interplay between the a weakened granular structure as result of interruption of the inter- and intra-molecular bonds, and reduced bonding with water molecules as a result of the hydrophobicity of the acetyl groups, the viscosity of the final product can be enhanced.

Acetylation improves paste clarity and freeze-thaw stability of starch. Starch acetates of low DS are commonly used in the food industry for quality consistency, and as texture and stability enhancers. The Food and Drug Administration (FDA) maximum DS of acetylated starches for food application is 0.1 [19]. Starch acetate of high DS exhibit high degree of hydrophobicity and thermoplasticity and are soluble in organic solvents like chloroform and acetone, and are mostly used in nonfood applications [25]. At 0.0275 DS, corn starch exhibit lower paste gelling, which is practically lost at 0.05 DS. Most commercial starch acetates have <0.05 DS [19].

Acetylated distarch adipate, is a monosubstituted starch obtained by treating starch with acetic anhydride and adipic anhydride (Figure 6). It has been used since the 1950s due to desire for improved stability of product in cold and freezing weather conditions. It is a good temperature change resistant agent used in foods as a bulking agent, stabilizer and thickener. It improves smoothness and sheen of soups and sauces [19]. The improved freeze-thaw stability of acetylated crosslinked waxy maize starch has led to its use in frozen sauces in vegetables, appetizers and pastries. Hydroxypropylation of cross-linked starch also dramatically improves the stability quality of puddings and frozen sauces [19].

#### 4.1.2.2 Succinylation of starch

When starch granule is esterified with succinic anhydride, it produces succinyl starch, and the process is commonly referred to as succinylation of starch. Succinylation of starch was earlier achieved in the presence of aqueous pyridine and under reflux at 115°C (Figure 7). However, environmental concerns have led to the development of more green synthetic routes. Thus succinic ester of starch have been prepared by mixing starch with succinic anhydride solution in acetone and refluxing at 110°C for 4 h [25]. Sui et al. [26] was also able to induce a reaction by drop-wise addition of succinic anhydride to a water suspension of starch while maintaining pH at 8.5 by drop-wise addition of sodium hydroxide.

Succinyl group weakens the inter-molecular bonding of starch polymeric chains in the granules, facilitating swelling, solubilisation and gelatinization at lower temperatures. Paste clarity is enhanced and retrogradation is reduced. However, there

#### Figure 6. Esterification of starch with acetic anhydride and adipic anhydride.

Chemical Properties of Starch and Its Application in the Food Industry DOI: http://dx.doi.org/10.5772/intechopen.87777

Figure 7.

Succinylation reaction of starch.

may be reduced stability against shear at high temperature and during cooling. Starch succinate is ionic and acts as polyelectrolytes. At low degree of substitution (DS), the succinate makes the starch more hydrophilic and viscos in solution [8, 25]. For its viscosity enhancing effect, succinylated starches could find application in production of non-gelling custard creams, and for its increased hydrophilicity, it could be used for enhancing the juicy/smooth taste of meat and fried products. Starch succinates can also be used in soups, snacks, and frozen/refrigerated food products as thickening or stabilizing agents.

Esterification of starch with octenylsuccinic anhydride (OSA) or octenylsuccinic acid in the presence of an alkali yields starch octenylsuccinate (Figure 8), while esterification with dodecyl succinic acid yield starch dodecyl succinate. The octenyl or dodecyl group introduce a reasonable level of lipophilicity to the product making it have dual functionality which can be used in emulsification and flavours encapsulation. OSA treated starches are used to stabilize oil-in-water food emulsions associated with beverage concentrates containing flavor and clouding oils [19]. It helps to protect emulsified and spray dried flavour oils against oxidation during storage. FDA allows a DS of 0.02.

Commercial production of acetylated starch dodecyl succinate, di-substituted starch of low dodecyl succinate residue employs acetic anhydride reagent at alkaline pH [15]. An alkali-starch complex forms first, which then interacts with the carboxylic anhydride to form a starch ester with the elimination of carboxylate ion and one molecule of water [15]. Starch succinate offers freeze-thaw stability, highthickening, low-gelatinization temperature, clarity of paste, good film-forming properties and resistance to retrogradation.

#### 4.1.2.3 Phosphorylation reaction

Inorganic esters also exist, for instance, esters of phosphorous acid (H3PO3) and phosphoric acid (H3PO4). When starch granules are reacted with phosphorylating agents such as phosphoric acid, mono- or di-starch phosphate is formed (Figure 9). The resulting starch has increased stability at high and low temperatures, more

Figure 8. Esterification of starch with octenylsuccinic acid anhydride.

#### Figure 9.

Phosphorylation reaction of starch.

resistant against acidic condition, and is applicable as a thickening agent. Orthophosphate and pyrophosphate has been used to achieve phosphorylation of starch under slightly acidic and high temperature conditions [27].

Phosphoryl trichloride (Figure 10), sodium tripolyphosphate (Figure 11) and sodium trimetaphosphate (Figure 12) have also been used under higher pH to obtain monostarch phosphate and di-starch phosphate [15, 28]. Phosphorylation reactions produce either monostarch phosphate or distarch phosphate which is a cross-linked derivative. However this depends on the reagents and reaction conditions. Usually, monoesters, rather than diesters, are produced with a higher degree of substitution [8]. Steric hindrance as a result of the introduced phosphate groups

Figure 12. Phosphorylation of starch with sodium trimetaphosphate.

#### Chemical Properties of Starch and Its Application in the Food Industry DOI: http://dx.doi.org/10.5772/intechopen.87777

inhibits the linearity of amylose or the outer branch of the amylopectin chain where it reacted. This weakens the inter-molecular association and creates chains disaggregation, which leads to better paste clarity [8].

Distarch phosphate has the phosphate group esterified with two hydroxyl groups of two neighbouring starch polymer chains [29]. The phosphate bridge or cross-linking strengthens the mechanical structure of the starch granules. Phosphate cross-linked starches exhibit stability against high temperature, low pH and shear, and improved firmness of the swollen starch granule as well as improved viscosity and textural characteristic. Distarch phosphate is used as thickener and stabilizer and provides stability against gelling and retrogradation and high resistance to syneresis during storage [8].

In solution, several specie of the phosphate ion can exist and anyone may be responsible for the phosphorylation reaction depending on the reaction conditions. Phosphorylation has been demonstrated to mostly occur at the C-3 and C-6 of the glucose units, and the degree of phosphorylation depends on distribution of the chain length of the starch polymers [30]. Blennow et al. [31] also demonstrated that phosphate groups may play important role in the size distribution of the amylopectin side chains of phosphorylated starches. Some researchers have reported that about 60–70% of total phosphorus of starch monophosphate is located at C-6 while the rest is located at C-3 of anhydroglucose units. Most phosphate groups (88%) are on chain β of amylopectin [9].

Landerito and Wang [32] reported that phosphorylated starch prepared by the slurry treatment exhibited a lower gelatinization temperature, a higher peak viscosity, a lesser degree of retrogradation, and improved freeze-thaw stability compared with those prepared by the dry-mixing treatment. They believed that phosphorylation probably occurred in both amylose and amylopectin chains, and the amount and location of incorporated phosphate groups varied with starch types, which may be due to their different amylose and amylopectin contents. Waxy starch was more prone to phosphorylation, followed by common and high-amylose starches. Enzymic phosphorylation of starch has been reported [33]. Extrusion condition of 200°C, sodium tripolyphosphate concentration of ≥1.4 g/100 ml and pH 8.5 have been used to obtain starch phosphate with high degree of substitution [34].

#### 4.1.3 Etherification

Generally, alcohols (▬OH) groups condenses with one another at high temperatures under acidic conditions to form ethers (Figure 13). The reaction mechanism is through a proton transfer from the catalyst to one of the molecule to form a cation, which loses the proton by extracting the ▬OH of the second molecule to form an ether and water.

Etherification of starch is usually done by use of epoxide reagents as depicted in Figures 14 and 15. The epoxides are first reduced to diols through a nucleophilic ring opening of the epoxide (cleaving the C▬O bond under aqueous, acidic or alcoholic condition) before the eventual condensation of one of the ▬OH group with that of starch [24]. Some etherification reactions occur under alkaline condition. Like esterification, etherification helps to mostly introduce lipophilic alkyl

$$\mathsf{R}^{\mathsf{I}}\mathsf{\cdot}\mathsf{O}\mathsf{\mathsf{H}}\quad\mathsf{+} \qquad \mathsf{R}^{\mathsf{2}}\mathsf{\cdot}\mathsf{O}\mathsf{\cdot}\begin{array}{ccc} \mathsf{R}^{\mathsf{2}}\mathsf{\cdot}\mathsf{O}\mathsf{\cdot} & \xrightarrow{\mathsf{H}^{\mathsf{1}}\mathsf{\cdot}\mathsf{\cdot}\mathsf{h}\mathsf{\cdot}\mathsf{R}^{\mathsf{2}}} & \mathsf{+} & \mathsf{\mathsf{H}}\_{2}\mathsf{\mathsf{O}}\\ \mathsf{F}\mathsf{\mathsf{the}} & & \mathsf{\mathsf{E}}\mathsf{the} \end{array}$$

Figure 13. Etherification reaction.

Figure 14. Etherification of starch with propylene oxide.

Figure 15. Etherification of starch with ethylene oxide.

groups into the starch chains thereby reducing the hydrophilicity and the degree of inter- and intra-molecular hydrogen bonding [8].

#### 4.1.3.1 Hydroxypropylation of starch

This reaction process produces hydroxypropylated starch (HPS), which is a starch ether produce by reaction of starch with propylene epoxide in the presence of an alkaline catalyst (Figure 14). HPS is used for enhancing stability and viscosity of food products. The hydroxypropyl groups introduced into the starch chains affect the inter- and intra-molecular hydrogen bonds, thereby allowing for more ease of displacement of starch chains in the amorphous regions [8]. HPS is more stable to prolonged high temperatures than starch acetate especially at pH 6, and has improves freeze-thaw stability. It is mostly used in refrigerated or frozen foods and in the dairy industry. The FDA allowable DS for HPS is 0.2 [19].

#### 4.1.3.2 Hydroxyethylation of starch

Hydroxyethylation of starch is performed by reacting starch with epoxyethane or ethylene oxide to produce the starch ether, hydroxyethylated starch (HES) (Figure 15). The health concerns of hydroxyethylated starch are limiting its use in the food industry. However they are mostly used in medicine and pharmaceuticals as plasma volume expander and extracorporeal perfusion fluids [35].

#### 4.1.3.3 Carboxymethylation of starch

This is an etherification reaction process where starch is reacted with sodium chloroacetate or chloroacetic acid under certain conditions to produce

carboxymethylated starch (CMS) (Figure 16). The reaction involves refluxing chloroacetic acetic acid with dry starch (anhydroglucose units) in the presence of sodium hydroxide in a solvent mixture of ethanol/isopropanol (ratio 3:5). Anhydroglucose unit can be obtained from acid hydrolysed starch [36].

#### 4.1.3.3.1 Cationization of starch

Another etherification reaction is cationization of starch in which starch react with electrophiles or electron-withdrawing reagents such as ammonium, amino, imino, sulfonium, or phosphonium groups to produce cationic starches (Figures 17–19), which are important industrial derivatives [15]. Cationic starches are usually prepared under alkaline conditions, and they exhibit higher dispersibility and solubility with better transparency and stability.

Cationic starches containing tertiary amino or quaternary ammonium groups are the most important commercial derivatives, however they are mostly used in the textile and paper industry.

For the production of sulfonium starch, halogenoalkyl sulfonium salts (e.g., 2-chloroethyl-methyl-ethyl sulfonium iodide or any β-halogenoalkyl sulfonium salt), vinyl sulfonium salts and the epoxy alkyl sulfonium can be used (Figure 19). Usually R<sup>1</sup> is unsaturated group like alkylene, hydroxyalkylene, aralkylene, cycloalkylene, and phenylene group, while each of R<sup>2</sup> and R<sup>3</sup> can be alkyl, aryl,

Figure 16. Etherification of starch with sodium chloroacetate.

Figure 17. Reaction of starch with aziridine to produce amino-ethylated starches [15].

Figure 18. Reaction of starch and dialkyl cyanamides to produce aminoalkyl starches [15].

Figure 19.

Etherification of starch with sulfonium salt to produce a sulfonium cationic starch.

aralkyl, cycloalkyl and alkylene sulfonium groups and may also contain ether oxygen linkages and amino groups [37]. Factors such as reagent used and temperature, affect the reaction period which usually takes about 16–20 h.

Sulfonium starch display positive charge and can be used as thickeners in the form of aqueous dispersions or pastes. These dispersions are made by heating the suitable amount of sulfonium starch and water to a temperature of approximately 93°C. Upon cooling, the resulting dispersion becomes considerably clearer and more resistant to viscosity change compared to the untreated starch. Starch succinate and starch citrates which are obtained through esterification reactions have also been observed to exhibit high cationic properties [8].

#### 4.1.4 Oxidation

Oxidation of starch with strong oxidizing agents mimics reaction of primary alcohols and diols. Primary alcohol ▬OH functions are oxidized (Figure 20) to its corresponding carbonyls (aldehydes and carboxylic acid), while vicinal diols (Figure 21) are cleaved by strong oxidants like periodic acid into its corresponding carbonyl compounds (aldehyde and/or ketones) [24]. Oxidation of secondary alcohol ▬OH produces ketones (Figure 22). Oxidation may result in breakage of some intra- and inter-molecular bonds and partial depolymerization of the starch chains [38].

Starches treated with oxidants fall into two broad classes: oxidized and bleached.

Figure 20.

Oxidation reaction of primary hydroxyl groups of alcohols.

$$\mathsf{R}^2\\\mathsf{C}\\\mathsf{H}\\\mathsf{(O\mathsf{H})}\\\mathsf{C}\\\mathsf{H}\\\mathsf{(O\mathsf{H})}\\\mathsf{R}^1 \xrightarrow{\begin{array}{c} \mathsf{I} \\ \end{array}} \begin{array}{c} \mathsf{R}^2\\\mathsf{C}\\\mathsf{O}\\\mathsf{(O\mathsf{H})}\\\end{array} + \begin{array}{c} \mathsf{O}\\\mathsf{(O\mathsf{R})}\\\end{array}$$

#### Figure 21.

Oxidation reaction of vicinal hydroxyl groups of alcohols.

Figure 22. Oxidation reaction of secondary hydroxyl groups of alcohols.

Chemical Properties of Starch and Its Application in the Food Industry DOI: http://dx.doi.org/10.5772/intechopen.87777

Figure 23. Oxidation reaction of starch to produce oxidized starch.

Oxidized starches are starches treated with oxidizing agents like sodium hypochlorite (NaOCl). The oxidizing agent can attack the glycosidic bonds hydrolysing them to alcohol (▬OH) functions or/and C▬C bonds of the glucose unit, oxidizing them to carbonyl functions of aldehydes, ketones and carboxylates (Figure 23). Higher pH favors formation of carboxylate groups over aldehydes and ketones. Some depolymerization usually occurs in the process. Introduction of carboxylate groups provides both steric hindrance and electrostatic repulsion. Oxidation is usually carried out on whole granules and it causes the granule to dissolve, rather than swell and thicken [19]. The reaction can introduce up to 1.1% of carboxyl groups in the granule [39]. Oxidation with chlorine or sodium hypochlorite reduces the tendency of amylose to associate or retrograde. The reaction rate of starch with hypochlorite is remarkably affected by pH, which tend to be higher at about pH 7 but becomes very slow at pH 10 [40]. Oxidized starches are used where intermediate viscosity and soft gels are desired, and where the instability of acid-converted starches is unacceptable [41]. Hence, pastes of oxidized starches have a lower tendency to gel compared to those of thin-boiling (or acid hydrolized) starches of comparable viscosity.

Other oxidants such as chlorine, hydrogen peroxide and potassium permanganate, dichromates and chlorochromates, etc. are less commonly used. Oxidized starches are reported to give batters improved adhesion to meat products and are widely used in dough and baked foods [41].

Bleached starch is obtained from oxidation of starch with lower concentrations of oxidizing agents like hydrogen peroxide, sodium hypochlorite, potassium permanganate or other oxidants used to remove color from naturally occurring pigments. Bleaching is done to improve the whiteness and/or eliminate microbial contamination. Reagent levels of about 0.5% are usually used, and loss of some starch viscosity due to hydrolysis usually occurs.

#### 4.1.5 Cross-linking of starch

Cross-linking of the starch polymer chains with reagents that could form bonds with more than one hydroxyl group of molecule results in cross-linked starch. Such reactions randomly add inter- and intra-molecular bonds at different locations in the starch granule which helps to strengthen and stabilize the polymers in the granule. Such processes may employ hydrolysis, oxidation, esterification, etherification, phosphorylation or combinations of these methods in a sequential or one-mix procedure to achieve the desired product that meets the required physicochemical characteristic of gelatinization, viscosity, retrogradation, and textural properties for food applications. In some instances, multifunctional reagents capable of forming either ether or ester inter-molecular linkages between hydroxyl groups on starch molecules are used. Reactions usually take place at the primary ▬OH group of C-6 and secondary ▬OH of C-2 and C-3 of the glucose units. Epichlorohydrin monosodium phosphate, phosphoryl trichloride, sodium trimetaphosphate, sodium tripolyphosphate, a mixture of adipic and acetic anhydride, and vinyl chloride are the main agents used to cross-link food grade starches [15]. Di-starch phosphate (Figure 12) which is a phosphorylated starch is an example of a crosslinked starch. Acetylated distarch adipate (Figure 6), hydroxypropyl distarch phosphate, hydroxypropyl distarch glycerol are other examples of crosslinked starch [8]. The FDA specify that not more than 0.1, 1 and 0.12% DS (w/w of starch) of phosphoryl chloride, sodium trimetaphosphate and adipic-acetic mixed anhydride, respectively, should be used for food grade starch [19].

Cross-linked starch exhibit increased resistance to processing conditions such as high or low temperatures and pH. Cross-linking reduces granule rupture, loss of viscosity and the formation of a stringy paste during cooking, providing a starch suitable for canned foods and products. Cross-linked starch shows smaller swelling volume, lower solubility and lower transmittance than native starch [15]. While oxidation may increase retrogradation, crosslinking reduces it. Hence a combination of the two chemical modification methods can be used to get the starch with desired balanced characteristics.

#### 4.1.6 Approaches to modification of starch

As mentioned in the introductory section, native starches are modified to improve their physicochemical properties due to different reasons. Different approaches have been reported including physical, chemical, enzymatic and genetic approach. But the most widely used is the chemical approach. For instance, since starch must be gelatinized for it to be digestible in human diet and nutrition, and the process of gelatinizing native starches usually takes appreciable amount of time for granule to swell and form paste of gel as obtained in cooking rice and corn flour porridge, it can be modified to reduce gelatinization time by physical methods such as extrusion, spray-drier and drum dryer, which promote fast starch gelatinization to produce pregelatinized starch [42–44]. Pre-gelatinized starch exhibit reduced gelatinization temperature and time. The modified starches are usually dries to obtain flours and/or pre-gelatinized starches of long-term stability and quick preparation [9]. Pregelatinized starches are partially or totally soluble in cold water and readily form pastes [45]. It absorbs more water and disperses readily in water than the untreated starch, forming gel at room temperature and less prone to deposit [46]. Using gelatinized starch in food products affects the food qualities and properties, such as, bread volume and crumb [47]; pastas elasticity and softness, lusciousness and digestibility, tolerance in the properties of beating and cake mixtures, ice creams, doughnuts, growth of sugar crystals in food products [48]; texture, volume, shelf-live and stability during thawing of cakes and breads [49]. Liquefaction, partial hydrolysis and dextrinization may occur during pregelatinization depending on the processing conditions [42–44].

The process of physical modification does not involved any chemical reaction of starch with a modifying reagent and is referred to as physical modification of starch and the products are known as physically modified starches. However, most modifications of starches are performed through chemical processes. The chemical

#### Chemical Properties of Starch and Its Application in the Food Industry DOI: http://dx.doi.org/10.5772/intechopen.87777

reactions of starch (hydrolysis, esterification, etherification, oxidation and cationization) are generally exploited in the industry to produce converted or modified starches fit for different purposes in the industry.

According to the Food and Nutrition Program (FNP) of the FAO [50], a modified starch is a food starch which has one or more of its original physicochemical characteristics altered by treatment in accordance with good manufacturing practice by one of the reaction procedures such as hydrolysis, esterification, etherification, oxidation and cross-linking. For starches subjected to heating in the presence of acid or with alkali, the alteration (mainly hydrolysis) is considered a minor fragmentation. Bleaching is also essentially a process resulting in the colour change only. However, oxidation involves the deliberate creation of carboxyl groups. Treatment of starch with substituting reagents such as orthophosphoric acid etc., results in partial substitution in the 2-, 3- or 6-position of the anhydroglucose unit (AGU) unless the 6-position is occupied for branching in amylopectin chain. For cross-linked starch, where polyfunctional substituting agent, such as phosphorus oxychloride, connects two chains, the structure can be represented by Starch▬O▬R▬O▬Starch, where R is the cross-linking group and Starch refers to the linear and/or branched structure [50].

Evolving biotechnological innovations are progressing with enzymatic and genetic modification of starch as a greener alternative to chemical modification due to environmental concerns. Enzymatic modifications basically employ hydrolytic enzymes found in certain bacteria. For instance amylomaltases or α-1,4-α-1,4 glucosyl transferases from Thermus thermophiles and cyclomaltodextrinase (CDase 1–5) from alkalophilic Bacillus sp. [48]. While α-1,4-α-1,4-glucosyl transferases breaks existing α-1,4 bonds and make new ones to produce modified starch used in foods and non-foods applications, CDase 1–5 can be used to produce starches which are low in amylose content without changing the amylopectin distribution. The granule of starch-cyclomaltodextrin complex produced special tastes and flavours, as well as light, heat and oxygen-sensitivity stability. Transglucosidase, maltogenic α-amylase and β-amylase have been used to produce resistant starches of various degrees of digestibility [8, 51, 52]. On the other hand, genetic modification employs biotechnology to targets the starch biosynthetic process. Genetic regulation of enzymes such as starch synthetase and branching enzymes, involved in starch synthesis through starch synthase genes are used to produces cereal crops that yield amylose- free starch, high-amylose starch and altered amylopectin structure in starch [8].

#### 5. Starch functionality and its applications in food

The reactions of starch explained above are exploited to create different types of modified or converted starched to obtain starches with appropriate physicochemical characteristics such as gelatinization, retrogradation, heat stability, solubility, transmittance, colour, texture, etc., for different industrial applications. The food industry is very mindful of safety of chemical residues hence not all types of modified starched are used in foods. Generally, modified starches are used for adhesion and as binder in battered and breaded foods, formed meat and snack seasonings; as dustings for chewing gum and products produced in the bakery; as crisping cover for fried snacks; fat replacer and juiciness enhancement in ice cream and salad dressings; flavour encapsulating agents in beverage clouds; emulsion stabilizers in beverages, creamers and canned foods; foam stabilizer in marshmallows; gelling agents in gum drops and jelly gum; and as expanders in baked snacks

and cereal meals [19]. Table 1 gives a summary of the chemical modification processes and their food application.

#### 5.1 Baked products (bread, pies, samosas, wafers, biscuits and sausages)

Baked products like biscuits, pies, bread, cakes wafers and sausages are high density products requiring heat resistant starches. Hence crosslinked starches are used since they are more resistant to oven baking temperatures of 120 ≥ 230°C. Gelatinized starches are also used in ready-to-eat cereal meals such as corn-flakes, etc. The temperature, humidity and degree of stirring determine the texture and quality of the product.

#### 5.2 Confectionery (candy, sweets and sweetmeat)

Oxidized starches have high clarity or transmittance, low viscosity and low temperature stability. It is frequently used in confectioneries for coating candies and sweets since they easily melt.

#### 5.3 Gravies, soups and sauces (soups, sauces, tomato paste or ketchup)

Etherified and crosslinked starches are mostly used. Crosslinked starched have higher stability for granules-swelling, high temperature resistant, high shear stability and acidic conditions stability. They are used as viscosifiers and texturizers in soups, sauces, gravies, bakery and dairy products. Etherified starches have improved clarity of starch paste, greater viscosity, reduced syneresis and freezethaw stability. Crosslinked starches are used in wide range of food applications such as gravies, dips, sauces, fruit pie fillings and puddings.

#### 5.4 Mayonnaises, salad dressing, ice cream, spreads and beverages

Hydrolyzed and esterified starches are mostly used in salad dressing and beverages. Hydrolyzed starch (acid-modified starches) has lower paste viscosity under cold and hot conditions. Hence they are used in mayonnaises and salad dressing [19]. Esterified starches have lower gelatinization temperature and retrogradation, lower tendency to form gels and higher paste clarity, and are used in refrigerated and frozen foods, as emulsion stabilizers and for encapsulation of beverage clouds. OSA starch is used as emulsifiers in mayonnaises and salad dressings.

#### 5.5 Pasta (spaghettis, macaroni, others)

Pregelatinized and crosslinked starches are mostly used in pastas. Gelatinized starch affects pastas elasticity and softness, delectableness and digestibility. Crosslinking gives the needed structural firmness to the pasta.

#### 5.6 Puddings (custard, pap, others)

Pregelatinized starches are used in puddings, instant lactic mixtures and breakfast foods to achieve thickening or water retention without employing heat. They are also used in ready-to-use bread mixtures. They are used where little or no heat is required and the increased absorption and retention of water improves the quality of the product; as an agglutinant in the meat industry; and as a filling for fruit pies [9, 49].


#### Chemical Properties of Starch and Its Application in the Food Industry DOI: http://dx.doi.org/10.5772/intechopen.87777



Table 1. Applicationof

 chemically

modification

 starches in foods.

Chemical Properties of Starch and Its Application in the Food Industry DOI: http://dx.doi.org/10.5772/intechopen.87777

#### 6. Conclusion

The importance of starch as a biopolymer continues to be on the upward trend due to its versatility. It has transformed from its traditional use as energy-source food to more sophisticated food and non-food applications. Its growing relevance in modern technological application is as a result of its susceptibility to modification, which transforms the native properties into more desirable and malleable characteristics fit for different purposes. These modifications are only possible due to the chemical reactivity of the constituent glucose monomers of the starch chains. Though the starch granule is inherently almost unreactive, it is however easily activated for reaction by certain conditions such as high or low pH, higher temperature, presence of a catalyst, etc. Under the right condition, starch molecules can undergo hydrolysis, oxidation, esterification and etherification reactions to produced products of improved organoleptic, textural, mechanical and thermoplastic properties of desirable foods and non-foods application. Modified starches like starch acetate, starch phosphate, HPS, CMS, sulfonium starches and their crosslinked derivatives are used for various applications in the food industry. However, concerns for chemical residues in these products and environmental considerations for hazardous chemicals used in some of the process, have led to more studies for greener modification processes. Though biotechnology has evolved enzymic and genetic modification processes for production of some modified starches, they are still highly limited and sometimes uneconomical, hence chemical modification remains the most versatile and mostly used.

### Conflict of interest

The author declares no conflict of interest.

### Author details

Henry Omoregie Egharevba Department of Medicinal Plant Research and Traditional Medicine, National Institute for Pharmaceutical Research and Development (NIPRD), Abuja, Nigeria

\*Address all correspondence to: omoregieegharevba@yahoo.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Chemical Properties of Starch and Its Application in the Food Industry DOI: http://dx.doi.org/10.5772/intechopen.87777

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**Chapter 6**

## Application of Starch and Starch Derivatives in Pharmaceutical Formulation

*Christian Chibuogwu, Ben Amadi, Zikora Anyaegbunam, Benjamin Emesiani and Sabinus Ofoefule*

#### **Abstract**

Starch is a homo-glucose unit connected with glycosidic linkage. It is well known for its biodegradability, renewability, low cost, flexibility, and availability. However, to reach its potential in the pharmaceutical application, modification is necessary to solve the problem of solubility, retrogradation, and loss of viscosity. In this chapter, we discuss the different physical, chemical, enzymatic, and biotechnological modifications and their subsequent pharmaceutical application both as an excipient and directly as drug delivery vehicles. Overall, there were different characteristics conferred in a modification which were exploited in pharmaceutics, drug delivery, and antimicrobial preparation. We, however, believe that collation of the data on modification would go a long way toward standardizing the application of the modified products.

**Keywords:** starch, modification, pharmaceutical, drug, delivery

#### **1. Introduction**

Starch is the most abundant reservoir of carbohydrate in plants and a naturally occurring polysaccharide whose wide distribution makes it the second most abundant biomass material found in nature, only second to cellulose [1]. It is a product of the photosynthetic process in plants, storing the chemical energy of the sun in different parts of plants including the leaves of green plants, seeds, fruits, stems, roots, and tubers of most plants and making it available to nonphotosynthetic organisms with humans being the most significant beneficiaries. Starch is a polymeric molecule consisting of the six-carbon-ring glucose molecules with molecular weight varying from 104 to 107 Daltons and produced as discrete granules with distinct morphology in different plants [2–4]. Starch is formed in the chloroplasts of green leaves and amyloplasts of seeds, fruits, and tubers. Sources of starch include cereal grains such as corn, wheat, sorghum, rice, and tubers and roots such as cassava, potato, tapioca, yam, etc., which are all sources of dietary carbohydrates [5]. Beyond its natural usefulness as food, this polysaccharide has obtained wide acceptance in various industries such as in textile for stiffening fabrics, in the food industry as additives and thickeners among other uses, in the pharmaceutical industry as an excipient and more recently used as a drug carrier, and also in cosmetics and paper industries [1].

Starch is utilized either in its native form or in the modified form. Native starch refers to starch in its natural, unmodified state, as extracted from its plant source, while modified starch is one in which certain properties have been modified or altered to meet the desired specifications. In its native state, starch is unsuitable for many industrial processes mainly due to its poor solubility and also its inability to withstand industrial conditions such as high temperatures. Therefore, modifications are done not only to alter the physicochemical properties of starch and improve its technological value but also to exhibit desired qualities in finished products [5].

#### **2. Starch composition**

Structurally, starch is a polysaccharide composed of glucose (monosaccharide) units connected by α-D-(1-4) and α-D-(1-6) linkages. The starch molecule consists of two major types of polymers, namely amylose and amylopectin. Amylopectin consists of linear chains of glucose units linked by α-1,4 glycosidic bonds and is highly branched at the α-1,6 positions by small glucose chains at intervals of 10 nm along the molecule's axis, constituting about 70–85% of common starch. Amylose, on the other hand, is a linear chain of α-1,4 glucans with limited branching points at the α-1,6 positions and constitutes between 15 and 30% of common starch [2]. There are, however, exceptions to the rule in terms of glucan compositions (amylose/amylopectin ratio) of starches. This is because modifications have been introduced to starch molecules recently to alter the glucan composition to meet specific requirements with some starches genetically modified to have almost a 100% amylose content while some are designed to be amylose-free [3]. Irrespective of the source, the starch molecule is usually present as granules. However, the size and shape of starch granules depend on their botanical origin. For example, the granule size for rice starch is about 3–8 μm, while potato starch ranges from 15 to about 100 μm [4].

Starch granules have very complex structures, resulting from variations in their components. They also exhibit variations between amorphous and crystalline regions. The amorphous region of the granules consists of amylose associated with large branches of amylopectin molecules. On the other hand, the crystalline region consists of amylopectin molecules with short branches; therefore, the higher the amylopectin proportion in starch granules, the greater the crystallinity [5]. Starch granules have also been found to exist in varying shapes, including oval, round, elliptical, flattened ovoid, polygonal, lenticular, and disc shapes [4].

In addition to amylose and amylopectin, starch also contains other noncarbohydrate components such as lipids (up to 1%), residues of protein (0.4%), and a relatively small amount (<0.4%) of minerals (calcium, magnesium, phosphorus, potassium, and sodium) of which phosphorus occupies an important position [6, 7] (**Figures 1** and **2**).

**Figure 1.** *Structure of amylose [8].*

*Application of Starch and Starch Derivatives in Pharmaceutical Formulation DOI: http://dx.doi.org/10.5772/intechopen.88273*

**Figure 2.** *Structure of amylopectin [8].*

Lipids in starch are present in the form of phospholipids and free fatty acids and are usually associated with the amylose fraction. Lipids, particularly phospholipids, have great tendencies to form helical complexes with starch (mainly with amylose). The lipid complexes in starch granules are present as a hydrophobic nucleus situated within helices formed by amylose chains [9], and, although representing a small fraction of the starch granules, lipid complexes can significantly reduce not just the solubility of the granules but also the swelling capacity of the starch paste [7].

Phosphorus is a noncarbohydrate component of starch whose presence has been found to exert significant influence on functional characteristics such as clarity and viscosity of starch pastes. It is present either as monoester phosphates (proportionally associated with the amylopectin fraction by covalent bonds) or as phospholipids (proportionally associated with the amylose content of starch), with the latter significantly lowering these characteristics [10]. Properties such as solubility and transmittance of starch granules are also affected by the nature of the phosphorus present in the starch. It is reported that the presence of phosphorus in the form of monoester phosphates enhances these properties in starch granules [11].

#### **3. Properties of starch**

#### **3.1 Structure of starch granules**

X-ray analyses of starch granules reveal varying degrees of crystallinity of the granules. Three distinct X-ray patterns (A-, B-, and C-patterns) have been observed with the A-pattern's characteristic of cereal grain starches, such as maize, waxy maize, wheat, and rice, while the B-patterns are characteristics of tuber, fruit, and stem starches, such as canna, potato, sago, banana starches, and some mutant maize starches such as amylomaize-5 and amylomaize-7. C-type patterns are found in roots such as tapioca starch, beans, and peas and are an intermediate between A- and B-types [11]. Also B- and C-type native starches can be converted to the A-type by heat-moisture treatment (30°C for B-type and approximately 50°C for C-type). However, the original structure of the A-type starches needs to be destroyed and allowed to recrystallize for conversion into other crystalline forms to occur [12].

#### **3.2 Swelling capacity and solubility**

One of the characteristics of starch is the ability of its granules to absorb water. Water absorption results in swelling of the starch granule contributing to amylopectin-amylose phase separation and loss of crystallinity, which in turn promotes the leaching of amylose to the intergranular space [13]. Heating of starch molecules in excess water causes the breaking of its semicrystalline structure, allowing water molecules to interact (via hydrogen bonding) with the hydroxyl groups exposed on the amylose and amylopectin molecules. This association causes swelling and increases granule size and solubility. The extent of this interaction is influenced by the amylose-amylopectin proportion as the swelling capacity of the starch granule is a function of its amylopectin content. The high tendency of the amylose component of starch granules to complex with phospholipids (forming amylose-lipid complexes) greatly inhibits the solubility and, consequently, the swelling capacity of starch granules [11].

#### **3.3 Gelatinization of starch**

Starch, when heated in excess water, undergoes a transition phase known as gelatinization. Gelatinization of starch is useful in particular industries, especially the textile and hydrolyzed starch industries. Generally, starch gelatinization can be defined as the conversion of starch from the crystalline, granular form to the dispersed and amorphous state [6]. Gelatinization occurs when water diffuses into the granule, which then swells substantially due to hydration of the amorphous phase causing loss of crystallinity and molecular order [14]. The gelatinization temperature of the starch granules varies depending on the source of starch. This is due to the influence of the organization (packing of the double helices) of the glucan chains in the crystalline lamellae of the granules. This includes the nature of the branching pattern (distance between the branching points and numbers of chains in the building blocks) and the length of external chains. Other factors include the concentration of amylose and the lipid content of the starch. Chemical methods of starch gelatinization and consequent solubilization are also available such as the use of alkali (NaOH) and dimethyl sulfoxide (DMSO). However, the conditions and pathways of gelatinization are different from the process of boiling water. For instance, apart from occurring at a low temperature (20°C), starch granules do not swell in DMSO as they do in hot water but dissolve slowly by fragmentation of the interior of the granule into smaller pieces [15].

#### **3.4 Retrogradation**

Retrogradation refers to the molecular interaction produced after gelatinization and cooling of the starch paste, that is, the recrystallization of glucan chains in gelatinized starch. It can be described as the tendency for solvated, amorphous starch to return to an insoluble, aggregated, or crystalline state when stored at a temperature above its glass transition temperature. This characteristic of starch is favored both by low temperature (0–5°C) and high starch concentration [6]. This property is one of the causes of staleness of baked products during storage and is generally considered unfavorable in terms of food quality. The glucan composition (amylose/amylopectin ratio of starch), as well as the presence of other noncarbohydrate components, has a significant influence on the retrogradation potentials of starch. For instance, high amylose content increases retrogradation potentials of starch, whereas amylose-free starches have less tendency towards this behavior. This is because, during retrogradation, amylose molecules associate with other

glucose units to form a double helix, while amylopectin molecules recrystallize through the association of its small chains [11]. The presence of other components such as proteins, lipids, other carbohydrates, salts, and polyphenols significantly affects retrogradation. For example, proteins can complex with starch to retard the retrogradation process during refrigerated storage [16].

#### **4. Starch modification and pharmaceutical application**

The abundance, biodegradability, and cost-friendly characteristics of starch make it an important raw material for many industrial processes. However, certain properties of starch make it undesirable for all applications. Most native starches are limited in their direct application due to poor solubility in water and a strong tendency for decomposition and retrogradation. They also display high instability with respect to changes in temperature, pH, and shear forces [15]. Therefore, starches are often subjected to either physical, chemical, or enzymatic modifications. These modifications are done to develop specific properties such as solubility, hydrophobicity, thermal stability, amphiphilicity, paste clarity, mechanical strength, freezethaw stability retrogradation resistance texture, adhesion, and tolerance to high temperatures used in industrial [6, 17].

Several factors affect the digestibility of native starch and, hence, possible pharmaceutical application. These include amylopectin: amylose ratio, amylopectin chain length, degree of crystallinity, and intermolecular association in granules [17]. Modification typically affects all these properties, and the choice of modification can lead to customization and flexibility in starch use.

Summarily, these are modification methods currently in use:

#### **4.1 Physical modification**

Physical treatments are generally divided into thermal and nonthermal treatments. Thermal treatments involve the use of heat to rearrange the amylopectin: amylose ratio and length of chain. This typically leads to highly soluble excipients, and when exposed to such temperature conditions, gelatinization occurs, improving the swellability and solubility. Thus starch produced in this manner is easily plasticized and can be used in the production of antimicrobial films and also as superdisintegrants.

Thermal treatments include pregelatinization, heat-moisture treatment, annealing, dry heating, and osmotic pressure treatment.

Pregelatinization involves the starches to be cooked at a specified temperature and dried to allow little or no molecular reassociation.

Heat moisture treatment consists of heating starch granules at a temperature above the starch's glass transition temperature at the adiabatic condition with a relative humidity of 10–40% for 1–24 h [17]. The changes observed show no crystallinity in A-type; however, B-type starch granules change to C-type. Increase in crystallinity, however, is only a desired trait in sustained release formulation [17].

The nonthermal treatment includes ultrasonic treatment, milling, high-pressure treatment, pulsed electric field, freezing/thawing, and freeze-drying treatment.

#### **4.2 Chemical modification**

This involves the insertion of a new functional group on the starch backbone to give unique properties to the starch. There are numerous methods of chemical modification, but the most relevant are acid hydrolysis, cross-linking, acetylation, dual modification, oxidation, and grafting.

#### **4.3 Enzymatic modification**

The enzymatic modification of starch targets the amylopectin: amylose chain length and content and also the molecular weight. Typically, when the mentioned variables are reduced, the modified starch can be used to formulate fast-releasing micro and nano-particles. Alternatively, used in immediate release tablet formulation. The modification, however, does not improve the swellability of the starch granules, and as such, it cannot be used as a disintegrant.

#### **5. Advances of modified starch in some drug delivery application**

The modification of starch has given it some controlled delivery in drug delivery system, and depending on the modification carried out in the starch, such as acid modified, pre-gelatinized, freeze-dried, cross-linked, and hydroxypropylation, the disintegration and binding properties are affected. This can subsequently affect the rate of release.

A study was done by Alexiou et al. [18] to study the biocompatibility of starch as a carrier to targeting cancer cells. Phosphate-modified starch was used to prepare iron oxide nanoparticle, which was then mixed with mitoxantrone. The iron oxide nanoparticles improved drug concentration and targeting using a magnetic field. This improved the in vivo effect.

Rice starch modified with carboxylation and oxidation [20] was used in the tablet preparation of metronidazole. It was found out that the starch conferred a controlled release mechanism owing to its enzymatic and pH resistance leading to a slow-release with prolonged effect.

Thermosensitivity of starch derivative was recently tested in the drug delivery system. Acid-hydrolyzed starch treated with butyl glycidyl ether to yield 2-hydroxy-3-butoxypropyl starch polymer micelles was loaded with prednisolone and the in vitro dissolution profile investigated in distilled water at 20 and 40°C. It was discovered that 38% of the drug was released at 20°C, while 90% was released at 40°C. The effect of molar substitution (MS) and lower critical solution temperature (LCST) of the modified starch offered a mechanism to this release. The above factors were investigated and discovered to be inversely proportional, thus, when MS was doubled from 0.32 to 0.67, the LCST decreased from 32.5 to 4°C. This increase in molar substitution affects the micelles leading to swelling and controlled release at different temperature [20].

Antimicrobial agents have low molecular weight and can display poor retention, and easily leaking out without attaining stability in the formulation. This has provided the rationale for conjugating the antimicrobials with high-molecularweight starches which prevent leaching and improve the encapsulation efficiency. A work done by Guan et al. [20] showed the microbicidal effect of covalently bonded polyhexamethylene guanidine hydrochloride (PHGH) and potato starch on the activity of nonresistant *Escherichia coli* and *Staphylococcus aureus*. The microbial growth was inhibited to almost 100% when 1% of the PHGH was used in the modification [28].

There is no direct compilation of how the different modifications affect the inherent properties of native starch to the point of predictive usage, but the effect is always felt in the modification technique used and the observed pharmaceutical function. Below is a tabulated list of some of the current usages of modified starches in drug delivery systems (**Tables 1** and **2**).


#### *Application of Starch and Starch Derivatives in Pharmaceutical Formulation DOI: http://dx.doi.org/10.5772/intechopen.88273*

#### **Table 1.**

*Antimicrobial modified starch and its activities.*


#### **Table 2.**

*Modified starch and their application towards drug delivery systems.*

### **6. Conclusion**

The role of starch keeps diversifying. The pharmaceutical potential of modification of starch in drug delivery systems has been shown in this report to vary and is not easily predictable until the final outcome. It is our recommendation that documenting the observable physical and molecular change in the starch modification alongside with the observable drug delivery effect would improve the predictional use of this versatile material.

### **Author details**

Christian Chibuogwu\*, Ben Amadi, Zikora Anyaegbunam, Benjamin Emesiani and Sabinus Ofoefule Institute for Drug-Herbal Medicine-Excipient Research and Development, University of Nigeria, Nsukka, Nigeria

\*Address all correspondence to: christian.chibuogwu@unn.edu.ng

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Application of Starch and Starch Derivatives in Pharmaceutical Formulation DOI: http://dx.doi.org/10.5772/intechopen.88273*

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[23] Balmayor ER, Tuzlakoglu K, Azevedo HS, Reis RL. Preparation and characterization of starchpoly-ε-caprolactone microparticles incorporating bioactive agents for drug delivery and tissue engineering applications. Acta Biomaterialia. 2009;**5**:1035-1045

[24] Liu C-S, Desai KGH, Meng X-H, Chen X-G. Sweet potato starch microparticles as controlled drug release carriers: Preparation and in vitro drug release. Drying Technology. 2007;**25**:689-693

[25] Szepes A, Makai Z, Blümer C, Mäder K, Kása P, Szabó-Révész P. Characterization and drug delivery behaviour of starch-based hydrogels prepared via isostatic ultrahigh pressure. Carbohydrate Polymers. 2008;**72**:571-578

[26] Malafaya PB, Stappers F, Reis RL. Starch-based microspheres produced by emulsion crosslinking with a potential media dependent responsive behavior to be used as drug delivery carriers. Journal of Materials Science. Materials in Medicine. 2006;**17**:371-377

[27] Jain AK, Khar RK, Ahmed FJ, Diwan PV. Effective insulin delivery using starch nanoparticles as a potential trans-nasal mucoadhesive carrier. European Journal of Pharmaceutics and Biopharmaceutics. 2008;**69**:426-435

[28] Zaki Ahmad M, Akhter S, Ahmad I, Rahman M, Anwar M, Jain GK, et al. Development of polysaccharide-based colon targeted drug delivery system: Design and evaluation of Assam bora rice starch-based matrix tablet. Current Drug Delivery. 2011;**8**:575-581

[29] French D. Organization of starch granules. In: Whistler RJ, BeMiller JN, Paschall EF, editors. Starch: Chemistry and Technology. 2nd ed. New York: Academic Press; 1984. pp. 200-210

Section 3 Resistant Starch

#### **Chapter 7**

## Resistant Starch from Exotic Fruit and Its Functional Properties: A Review of Recent Research

*Lee-Hoon Ho and Shi-Yun Wong*

#### **Abstract**

Resistant starch is a functional food ingredient that can resist enzymatic digestion in the small intestine and fermentation in large intestine. Resistant starch has many benefits to human health by promoting a balanced blood sugar and beneficial gut bacteria. This review highlighted the sources of different exotic fruit starch, such as banana, jackfruit, *cempedak*, *durian*, and breadfruit. The functional properties of these exotic fruit resistant starches were covered in this review. The effect of resistant starch on glycaemic index of food was revealed. This review also discussed on the applications of resistant starch in the production of food products and their effects on food quality. The provided information through the overall review could especially benefit the food industry in producing functional food products with great consumer acceptability.

**Keywords:** resistant starch, banana, jackfruit, *cempedak*, *durian*, breadfruit, functional properties, glycaemic index, product quality

#### **1. Introduction**

Starch is the main glycaemic carbohydrate reserve in plants, including cereals, tubers, roots, and unripe fruits. Starch is considered the second largest natural biopolymer next to cellulose [1]. Dietary starches are important sources of energy for the majority of the world's population. Starch is a polymer with molecular formula (C6H10O5)n and contains two d-glucopyranose polymers, namely, amylose and amylopectin. Amylose is a glucopyranosyl linear polymer, whereas amylopectin is a glucopyranosyl chain polymer [2]. It contributes up to 70–80% of total carbohydrates in human diet. Starch plays a major part in human nutrition by supplying metabolic energy that enables the body to perform its different functions [3]. Nowadays, dietary guidelines are focused on lowering fat intake by increasing complex carbohydrate intake (i.e. starch and dietary fibre) [4].

Nutritionally, starch can be grouped based on its rate and extent of digestion: rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) [5]. Recently, the consumption of RS in daily diet has gained increasing worldwide attention due to its health-promoting benefits and functional properties. The starch molecules undergo several physical modifications, depending upon the type of starch and severity of the conditions applied during processing of starchy foods, leading to RS formation [6].

#### *Chemical Properties of Starch*

RS positively influences the functions of the digestive tract, microbial flora, blood cholesterol level, and glycaemic index (GI) and assists in the control of diabetes [3]. Apart from the potential health benefits of RS, another positive advantage is its lower impact on food sensory properties than traditional fibre sources. Starch contributes to the physicochemical properties of food products which are made from cereals, tubers, roots, legumes, and fruits. Among its desirable physicochemical properties are its swelling capacity, viscosity, gel formation, and water-binding capacity, which make starch useful in a variety of food [7].

Starch digestion rate is affected by the nature of food composition (e.g. phosphorylated starch, RS, dietary fibre, phytonutrients, protein, and fat content) [8]. In addition, the types of chemical structure and physicochemical properties of starch and fibre present in food are important to determine their effects in the gastrointestinal tract [9]. The types of carbohydrate as well as total amount of carbohydrates in food will affect the blood glucose level [10]. According to Foster-Powell et al. [11], different digestibility rates of carbohydrate is related with some physiological functions, which have different health effects, for example, reduction in insulinemic and glycaemic responses to food, hypocholesterolemic action, and protective effects against colorectal cancer.

The functional properties of starch must be considered when developing food formulations due to its influence on the quality of end products. Starch functional properties depend on the molecular structure composition of amylose and amylopectin together with the arrangement of their starch granules. Starch paste consistency depends on the gelatinisation degree and swelling power of starch granule. The paste texture is determined by viscoelastic deformation and depends on the strength of molecular bonds and amount of broken granules. In addition the paste or gel clarity varies from clear to opaque, and this property is related to light dispersion that results from the association between amylose and other components present in starch [12]. Therefore, the functional properties of the raw materials are influenced by variety, climate, and soil conditions where the plant is grown [13].

#### **2. Resistant starch (RS)**

Resistant starch is defined as a portion of starch that cannot be digested by amylases in the small intestine [14]. However, RS can be degraded through glycolysis by microorganisms in the colon even though at the first stage it cannot be digested or absorbed by amylase in the human digestive tract [15, 16]. RS was introduced in recent years as a functional food ingredient important to human nutrition. RS has become an attractive functional food ingredient in food processing among food manufacturers to develop new nutritional food products [16]. The RS degree of formation in food depends on the type of starch contained and adopted processing conditions, such as water content, pH, heating temperature and time, number of heating and cooling cycles, freezing, and drying. It is also influenced by the duration and storage conditions [17–19]. Moreover, Eroglu and Buyuktuncer [19] reported that cooking methods like steaming, baking, and autoclave cooking increased the amount of RS in food, whereas pressure cooking was found to decrease the amount of RS in food. Cooking methods, such as boiling, microwave heating, extrusion, and frying, have the potential to increase the amount of RS, depending on the source of starch and processing conditions.

RS content is an important parameter to be considered mainly from the nutritional point of view as starch in this form is less easily digested and may impart health benefits [20]. In addition, RS was revealed to have various health benefits,

#### *Resistant Starch from Exotic Fruit and Its Functional Properties: A Review of Recent Research DOI: http://dx.doi.org/10.5772/intechopen.88816*

including the prevention of colon cancer, inhibition of fat accumulation, reduction of gall stone formation, increase in absorption of minerals, hypoglycaemic and hypocholesterolemic effects, and acceleration of probiotic growth [21]. A diet high in RS can reduce blood cholesterol and triglyceride levels due to higher excretion rates of cholesterol and bile acids [22].

RS has a unique equivalent behaviour to fibre which can escape from enzymatic digestion in the small intestine but be fermented in the large intestine by colonic microflora to serve as source of nutrient for the colonic bacteria [5, 23]. When the carbohydrate metabolises, it lowers the colonic pH and releases short fatty acids, such as propionate, butyrate, and acetate, to encourage the spread of beneficial bacteria in the intestine [18, 21, 24]. RS plays a vital role in health food manufacturing [5]. With its unique characteristic that is resistant to human digestive enzymes, RS is slowly broken down throughout the entire small intestine and then produces a slow release of glucose, and thus acts as an evidence for the low GI of indigested starch [25]. This can help to reduce postprandial response and promote glucose regulation in diabetes and control body weight for the obese, reducing glycaemic and insulinemic responses to food [26, 27].

There are five general subtypes of RS fraction in food: type 1 RS (RS I), type 2 RS (RS II), type 3 RS (RS III), type 4 RS (RS IV), and type 5 RS (RS V) [28]. The RS fractions are classified based on the nature of starch in food [5]. For RS I, it is corresponded to the physically inaccessible starches which are entrapped in the cellular matrix found in whole grains and seeds. RS II is native uncooked granules of some starches, such as starch in green bananas, raw potatoes, some legumes, and high amylose starches (i.e. high amylose corns), in which crystallinity makes them scarcely susceptible to hydrolysis. Meanwhile, RS III is retrograded amylose and amylopectin during food processing which causes a reduction in glycaemic response [29]. This starch is found in cooked and cooled food such as potatoes, bread, and corn flakes. Chemically modified starches generally belong to RS IV, and their molecular structures are chemically altered in many ways. RS IV is used by food manufacturers to improve the functional characteristics of starch [3]. RS V comprises amylose-lipid complexes, which have helical structures with fatty acid tails at the central cavities of the inclusion complex formed by alpha-amylase and polar lipids [5, 30]. These types of starch require higher temperatures for gelatinisation and are more susceptible to retrogradation [18].

#### **3. Functional properties of resistant starch produced from exotic fruits**

#### **3.1 Banana**

Several studies have reported that banana starch contains a high level of amylase that is often related to a high retrogradation [24, 31, 32]. Vatanasuchart et al. [31] reported that flour produced from indigenous banana cultivars has a high content of apparent amylose. Several reports revealed that consumption of green bananas confers beneficial effects on human health. This is often associated with their high content levels of RS, dietary fibre (i.e. non-starch polysaccharides), functional components, and other nutritive values [24].

In addition, green banana, which is a rich source of complex carbohydrates, is mainly RS and fibres, which is an important functional food [33]. Green banana starch is highlighted as one of the good substitutes for the starch industry [32]. Moreover, bananas are also a good source of energy due to the presence of a large amount of starch and sugar. The slow digestion of unripe plantain starch is associated with its starch granule properties (i.e. amylase and amylopectin), and its

physical characteristic is related to the plant cell wall that can contribute in lowering total starch gelatinisation [34].

Unripe bananas or green bananas were reported to contain high amount of RS II (i.e. ungelatinised starch granules that are protected from hydrolysis by the crystalline structure of the starch granule). The dense starch granules with crystalline structure property of green banana contribute to its high resistance to acid and digestive system enzyme (e.g. α-amylase) [35]. RS that is present in green banana helps to improve peptic ulcer and prevent damage of the mucosal lining [36].

A recent study showed that starch produced from the green banana variety of Mysore (Musa AAB-Mysore) had good physicochemical features and functional properties [37]. It is observed that starch from green variety of Mysore exhibited good swelling power which shows potential for its use in products that require water retention, such as meat and jellies. In addition, the low percentage of water loss during storage and low setback obtained by a folder profile study showed that starch is less prone to syneresis, which is one of the important factors to be considered during development of food products which require to be kept under refrigeration [37]. Fontes et al. [37] described the shape of starch granules of banana from the green variety of Mysore as ellipsoidal in shape with irregular diameters that range between axes of 10 μm and 100 μm and smooth surface. Another study done by Khawas and Deka [38] indicated that isolated culinary banana starch experienced restricted swelling and solubility profile and was unstable during freezing and thawing cycles. However, the starch demonstrated a high pasting temperature which indicated that culinary banana starches have high gelatinisation temperature and resistance towards swelling. Culinary banana starch exhibited a mixture of A-type and B-type polymorphs when observed under X-ray diffractometer. In addition, culinary banana starch has various functional groups which suggest C-type starch with a mixture of spherical and elliptical granules [38].

The banana starch was double-chemical modified by using two different cross-linking agents (i.e. phosphorus oxychloride and a mixture of sodium trimetaphosphate/sodium tripolyphosphate) [39]. The modified banana starch has a bigger average particle size than unmodified starch due to the swelling of the granules during chemical modification, and aggregates were also formed. The chemicalmodified banana starches presented an A-type X-ray diffraction pattern with slightly decreased crystallinity as compared to the unmodified banana starch. In addition, the modified starch decreased the temperature and enthalpy of gelatinisation and the decomposition temperature which were due to partial disorganisation during chemical treatment [39].

Many studies were conducted to produce and characterise the RS from banana starch; for example, González-Soto et al. [23] reported that banana starch is a good source for RS production by autoclaving after starch debranching. According to González-Soto et al. [23], banana starch without treatment has higher available starch (80.5%) and lower RS content (9.1%) than the banana starch that was debranched for 5 h and longer (70.0–77.5% for available starch and 14.5–18.5% for RS). A recent study done by Khawas and Deka [38] indicated that the RS III produced from culinary banana starch through enzyme debranching and hydrothermal process showed remarkable changes in physicochemical, functional, morphological, and thermal characteristics when different processing conditions were employed. It was reported that the modification of starch to RS III occurred due to retrogradation of the amylose fraction. Accordingly, the temperature and storage conditions enhanced its formation. Through analyses of scanning electron microscopy, Fourier transform infrared spectra, and thermogravimetric analysis, the results revealed various significant morphological changes and was observed with increase in starch concentration and elicited prominent modifications in enzyme-debranched RS [38].

#### *Resistant Starch from Exotic Fruit and Its Functional Properties: A Review of Recent Research DOI: http://dx.doi.org/10.5772/intechopen.88816*

Furthermore, starch from the peel of *Agung* banana, variety of Semeru, was isolated and characterised by Hadisoewignyo et al. [2]. The study reported that the characteristics of the resulting processed starch from *Agung* banana peel met the required specifications with regard to its form, taste, odour, and the presence of hyllus and lamellae. Hyllus is an initial point of starch formation, while lamellae are smooth lines surrounding the hyllus. However, the white colour index (~56°) of *Agung* banana peel starch did not meet the required specifications (i.e. 95°; white colour) due to an oxidation process that occurred during the starch preparation. In terms of the original shape of starch, starch isolated from the peel of *Agung* banana showed a small particle size [2] as compared to the elongated and cylindrical shape of green banana starch granules [40]. Moreover, the gel of *Agung* banana peel starch was reported to be twice more viscous than cassava starch gel, which made it very suitable as an ingredient in various food and nonfood industries including pharmaceutical industries, especially in making a tablet dosage form (i.e. tablet binder) [2].

Subrahmanyan et al. [41] reported that banana pseudostem contains 44.80% starch. The banana pseudostem was reported to contain high-quality starch [41, 42]. The study reported that starch granules of banana pseudostem are irregular in shape and are bigger in size than those of fruit starch. It also has similar intrinsic viscosity to that of potato starch. The amylose content of the banana pseudostem starch compare well with that of banana fruit and potato starch (21%) [42]. In addition, Ho et al. [43] reported that banana pseudostem was high in RS (12.81%). Since there is no updated scientific data related to the functional properties of the RS produced from banana pseudostem, there is an urgency to search for the functional properties of RS produced from banana pseudostem, so that it can be used to produce various value-added functional food products in the near future.

#### **3.2 Jackfruit**

Jackfruit (*Artocarpus heterophyllus*) seeds are considered as by-product of the canned and chips food industries. It has long been used as food among the indigenous people in many areas of the world. The seeds are usually consumed boiled, steamed, roasted, or are eaten as a snack [12]. Jackfruit seeds are recognised by many research studies as a raw material for a new source of starch [12]. The jackfruit seeds have been well documented to contain an average of above 60% dry basis of starch [44]. Native jackfruit seed can contain a reasonable amount of type II RS due to its relatively high amylose content 24–32% [45]. Jackfruit seed starch is widely used in many manufactured food products as it provides a gelling property that is suitable for various baked products [46]. According to Noor et al. [47], jackfruit seed flour contains amylose of 26.4–30.21% and starch content of 81.05–82.52%. In terms of proximate composition, the isolated starch from jackfruit seed was reported to contain 8.39–12.20% of moisture, 1.09–3.67% of protein, 1.18–1.40% of fat, and 0.03–0.59% of ash content. Moreover, the study reported that compared with alkali and enzyme methods, distilled water was the most effective solvent in the extraction of starch from jackfruit seed by presenting the highest yield, protein content, amylose, and total starch [47].

Jackfruit seed starch has been widely studied on its physicochemical, functional, and pharmaceutical properties [12, 48]. The results revealed that it had potential as functional ingredient for application in food and pharmaceutical products [44, 49]. Rengsutthi and Charoenrein [44] reported that starch from jackfruit seed had higher amylose content and its granules were much smaller than corn starch and potato starch granules. With regard to the pasting profile, jackfruit seed starch paste showed more resistance to thermal and mechanical shear during cooking. In addition, the jackfruit seed starch granules were round and bell-shaped, and some had irregular

cuts on their surface [12] with A-type crystallinity pattern [12, 44]. Zhang et al. [48] reported that the starches isolated from different varieties of jackfruit seeds, namely, four exotic jackfruit cultivars (i.e. *Artocarpus heterophyllus Lam*. cv. *Malaixiya No. 2*, *Malaixiya No. 3*, *Malaixiya No. 4*, *Malaixiya No.8*) and one local cultivar *Xiangyinsuo 1 hao*, had differences in average weight-average molar mass (Mw) of amylose and amylopectin and a fine amylopectin structure. The findings showed that jackfruit seed starch with a larger Mw of amylose and proportions of DP 25–36, DP ≥ 37, and chain length had lower peak viscosity, breakdown, final viscosity, setback, and adhesiveness but with a higher pasting and gelatinisation temperature, gelatinisation temperature range, gelatinisation enthalpy, and relative crystallinity. In addition, the local cultivar had lower amylopectin Mw, smaller particle size, and good amylopectin structure.

Kittipongpatana and Kittipongpatana [45] applied heat-moisture treatment to increase the yield of type II resistant jackfruit seed starch. It was reported that the native jackfruit seed contained approximately 30% w/w of type II RS and this amount was successfully increased to 52.2% w/w through heat-moisture treatment under the conditions of 25% moisture content, heating at 80°C for 16 h. In addition, thermal profile of the jackfruit seed RS showed an increase in the gelatinisation temperature as the moisture content was increased in the samples. Amylose contents of jackfruit seed RS exhibited a correlation trend with RS content. Jackfruit seed treated with heat-moisture treatment with higher RS demonstrated less swelling, while the solubility remained unchanged [45]. In addition, Madruga et al. [12] observed that the swelling power and solubility of jackfruit seed starch increased with increase in temperature, showing opaque pastes.

Jiamjariyatam [49] studied the effect of blends between wheat flour and jackfruit seed starch on the physical and chemical properties of batter coating. The wheat flour and jackfruit seed starch exhibited the A-type crystal form. Increasing jackfruit seed starch in blends was found to significantly increase amylose content and relative crystallinity in the starch mixture. An amylose content of 40–41% jackfruit seed starch was found to be suitable as batter coating for deep-frying.

#### **3.3** *Cempedak*

*Cempedak* (*Artocarpus integer (Thunb.) Merr.*) belongs to the Moraceae family, which is in the same family as jackfruit (*A. heterophyllus Lam*.) [50]. *Cempedak* seeds are the underutilised by-product from the fruit industry which have promising commercial value because they contain an appreciable amount of carbohydrate, protein, dietary fibre, minerals, and various vitamins, such as B1, B2, B3, and C [51]. Research was conducted to determine the composition of *cempedak* (ripe and unripe) between flesh and seed. Lim et al. [50] reported that unripe *cempedak* flesh and seeds had higher crude fibre than that of ripe *cempedak,* while both ripe and unripe *cempedak* flesh contained more crude fibre than the seed.

Starch extracted from *cempedak* seed was also studied by Tongdang [52] for its compositions and properties. The study reported that pure starch recovered from *cempedak* seed yielded 17.5%. The *cempedak* seed starch comprised approximately 22.64% of amylose and 16.12% of RS. Amylose content in fruit seed starch is related to its viscosity as amylose molecules may reassociate to form a gel network during the cooling time after starch gelatinisation [52]. Microscopic morphology of *cempedak* starch granules are semioval or bell-shaped but differ in size, mainly in the range of 1−10 μm. When *cempedak* starch granules are viewed under normal light, hilum in the centre of the granules is observed. On the other hand, Maltese cross indicates the semicrystalline structure of *cempedak* seed starch granules are shown under polarised light [52].

#### *Resistant Starch from Exotic Fruit and Its Functional Properties: A Review of Recent Research DOI: http://dx.doi.org/10.5772/intechopen.88816*

Important starch properties that affect the characteristic of starchy food were also investigated in a study by Tongdang [52]. *Cempedak* seed starches swelled up slowly at 55–75°C, but its swelling power was rapidly increased at 75°C and kept increasing until 95°C. The swelling power showed by *cempedak* seed starch well agrees with its pasting temperature of around 82°C. Meanwhile, solubility of *cempedak* seed starch was also rapidly increased after 75°C. According to Su et al. [53], several factors can influence the swelling power and solubility of starch, such as granular size, molecular structure of amylopectin, and amylose to amylopectin ratio and composition altered by contaminants. High gelatinisation temperature (76.76–82.19°C) of *cempedak* seed starch can be an indicator of a strong bonding of molecules in the granules.

The utilisation of *cempedak* seeds with its nutritional properties by processing it into flour has become a new source of fibre in bakery products. *Cempedak* seed flour provides a good source of total dietary fibre (TDF) and RS [51]. The presence of dietary fibre in food products to consumers is becoming important since it shows beneficial effects on the reduction of cholesterol level and colon cancer risk [51]. RS escapes digestion and absorption in the small intestine which has a similar effect to some dietary fibres by conferring a protective effect against colonic diseases [54]. According to Yamada et al. [55], RS helped lower the GI value of food products by increasing the indigestible carbohydrate ingested in small and large intestines.

A study by Aziz and Zabidi [51] showed that the processing of *cempedak* seed into flour resulted in a composition change. It was observed that *cempedak* seeds flour (CSF) has higher insoluble dietary fibre (IDF) content of approximately 23.93% with a reduced RS content of approximately 14.77% than the original IDF content of 12.44% and RS content of 29.72% found in *cempedak* seeds. According to Vasanthan et al. [56], heating followed by subsequent cooling and dehydration during processing may convert the starch in *cempedak* seed into indigestible form. In addition, the reduced RS content in CSF was caused by the microstructural damage of the seed during processing which affected the water absorption capability [57]. It was also observed that the soluble dietary fibre (SDF) in *cempedak* seed and CSF comprised 16.0 and 9.6% of the total amount of dietary fibre, respectively. Dietary fibre promotes beneficial physiological effects, including the prevention of diseases due to its potential in reducing the risks of cancer and coronary heart diseases [58].

Substitution of non-wheat flour (i.e. CSF) in conventional wheat bread to improve its functional properties was of great interest in recent studies. Zabidi and Aziz [59] reported that CSF substitution at 20 and 30% in bread formulation significantly increased the RS content in bread samples. The increased RS content reduced the hydrolysis index value which resulted in a lower GI. During bread making, starch gelatinisation upon heat treatment and followed by cooling process resulted in the formation of retrograded starch (RS3) [57]. Moreover, enzymeresistant amylose-amylose linkages that occurred upon retrogradation of starch aided in RS formation [60].

#### **3.4** *Durian*

*Durian* (*Durio zibethinus* Murr.) seed is a waste that is comprised of 20–25% of the whole fruit [61]. *Durian* seeds are mainly made up of starch and mucilage (gum). Properties of starch isolated from *durian* seeds to indicate its potential in food applications have become a great interest in recent studies. Based on previous studies, recovery of pure starch from *durian* seed showed a low yield of 1.8–4.2% [62] and 10.1% [52] as compared to other aromatic fruit seeds (i.e. 17.5% in *cempedak* and 18.2% in jackfruit). The low pure starch recovery was due to the presence of gum in *durian* seeds, which absorbed a large amount of water [63] that trapped

starch granules in a viscous suspension [64]. *Durian* seed starch showed an average granular size of 4–5 μm which was closely associated to the swelling power and viscosity of starch [52].

According to Tongdang [52], amylose and RS contents of *durian* seed starch were about 23 and 5%, respectively. Amylose content is crucial to functional properties of starch since high amylose is linked to high RS level in processed starchy food [65]. Starches that contain a low amount of amylose degrade faster than starches with a high amount of amylose [66]. Malini et al. [67] also reported that *durian* seed flour (DSF) contained 22.35% amylose and 66.33% amylopectin, suggesting that DSF contained similar amylose content with other common starch (i.e. tapioca). Amylose in the flour is important in the gel formation with a firm characteristic, while high amylopectin content is associated with the sticky property [68]. Flour with higher amylopectin content gelatinised faster [69] and reached a higher peak viscosity [67]. Due to similar amylose and amylopectin contents, it was found that DSF can be partially utilised to substitute tapioca flour as a filler ingredient in meatball without affecting its organoleptic quality [67].

A recent study of Baraheng and Karrila [64] was conducted to produce and characterise the *durian* seed flour and *durian* seed starch. The study reported that whole *durian* seed flour (WDSF) had lower starch content than demucilaged durian seed flour (DDSF), while durian seed starch (DS) contained the highest starch content. WDSF contains both starch and non-starch polysaccharides (gums). The removal of mucilage, which was considered a dietary fibre [70] led to an increase in starch content with a reduction in fibre content. *Durian* seed starch showed a pasting temperature of 76°C with its swelling power rapidly increased from 55 to 75°C [52]. Due to the presence of mucilage that enhanced water absorption [71], WDSF exhibited higher swelling power, water absorption capacity, peak viscosity, as well as emulsifying capacity and activity than that of DDSF and starch. However, WDSF showed the lowest gel hardness but highest syneresis in which water was released from gel at lower storage temperature [64]. These functional properties of WDSF suggest that it has potential to be used in hydrated product, emulsifier, and fat replacer, but it is not applicable in typical frozen food [64].

Innovative utilisations of the *durian* seeds as raw materials in food preparation is much encouraged. A recent study by Kumoro and Hidayat [72] on functional and thermal properties of fermented *durian* seed flour by using *Lactobacillus plantarum* revealed the potential of fermented *durian* seed to be used in the substitution of wheat flour as raw material. Fermentation produces acid and alters starch composition and morphology, increasing the gelatinisation temperature of *durian* seed flour (i.e. from 63.37 to 66.24°C) which is closer to that of wheat flour (i.e. 70.30°C) [72]. Mestres et al. [73] also described that fermentation may induce changes on the conformation of amylose and amylopectin in starch granules, which led to the alteration of gelatinisation temperature. On the other hand, fermented *durian* seed flour has higher fibre content and lower fat content, showing its superiority and high potential applications in food industry over wheat flour [72].

#### **3.5 Breadfruit**

Breadfruit (*Artocarpus altilis*) is rich in carbohydrates of approximately 76.7% [74] and has potential to be commercially processed into flour and starch. Breadfruit starch size is small with a granular size of 3.0–7.9 μm and is irregular in shape (i.e. spherical, elliptical, and polyhedral) [75]. Breadfruit starch has amylose and amylopectin content of 22.52 and 77.48%, respectively, and has moderately high breadfruit starch yield of 14.26%. It has shown its commercial value in industrial food utilisation [76]. In addition, the high amylose content of breadfruit starch and

#### *Resistant Starch from Exotic Fruit and Its Functional Properties: A Review of Recent Research DOI: http://dx.doi.org/10.5772/intechopen.88816*

its capacity to resist digestion suggest that products fortified with breadfruit can help to regulate blood sugar levels [76, 77].

Application of native breadfruit starch as food additive or functional ingredient is limited due to its poor paste clarity, readily retrograded characteristic [75]. Useful information gained from the study on breadfruit starch modification is necessary. In a study by Marta et al. [75], breadfruit starch was modified by using different thermal processes to characterise its physicochemical and pasting properties. Native breadfruit starches undergo changes in granule morphology, crystalline characteristic, pasting, and functionality due to heat-moisture treatment (HMT), microwave heating treatment (MHT), heat pressure treatment (HPT), and osmotic pressure treatment (OPT). Partial gelatinization, indicated by swelling, separation, and granular aggregation/fusion [78], caused HMT-treated and HPT-treated starches granules to lose their physical integrity. In addition, the X-ray diffraction pattern of the breadfruit starch changed from typical B type to A + B type due to HMT, MHT, and HPT, whereas OPT produced A-type breadfruit starch. Starch granules of A type and B type differed in their water content and packing of double helices [65] which were caused by the 36 water molecules vaporisation in the central channel of the B-unit cell and movement of a pair of double helices into the central channel [79]. Tan et al. [80] also described that transformation of crystalline structure of starch (i.e. from B type to A type) during HMT increased the SDS and RS contents in breadfruit starch. The higher compacity of A-type crystalline structure and the A-type amorphous lamellae which also had tight packing with higher density [81] could improve the enzyme resistance of starch during digestibility [80].

In respect to functional properties, thermal-modified breadfruit starch by using HMT, HPT, and OPT showed higher pasting temperature (i.e. ≥76.65°C) than native starch [75] due to the formation of a stronger crystalline structure (i.e. complex bonds between amylose in the crystalline region and amylopectin in amorphous region) which required water absorption of starch at higher temperature [82]. In addition, peak viscosity of thermal-modified breadfruit starch reduced significantly [75] which might be due to the increase in the extent of amylose-amylose and amylose-amylopectin chain interactions that occurred during the modification process [83].

Furthermore, breadfruit starch showed its potential use in fermented product indicated by previous studies. Haydersah et al. [84] observed that amylolytic lactic acid bacteria (ALAB) affected the digestibility of breadfruit starch by decreasing RDS content with an increase in RS content. Increased RS content in fermented breadfruit might be associated with the formation of limit dextrins that resulted from the action of α-amylase on amylopectin [84] as well as the formation of type 3 RS due to starch retrogradation during processing [8, 85]. With increased RS content after fermentation, breadfruit showed its value in the development of fermented products with prebiotic properties since RS can trigger increased production of short-chain fatty acids to stimulate the microbiota of the human gastrointestinal tract [86]. Fermentation also reduced apparent viscosity of gelatinised breadfruit flour and changed its consistency from a thick sticky gelatinised form into semiliquid/liquid product [84].

#### **4. Effects of resistant starch fortification on glycaemic index of food**

Nowadays, the public have great interest with regard to the possibility of controlling the blood glucose level by altering the glycaemic impact of carbohydrate intake. Glycaemic index is one of the preferred tools used for ranking food with regard to the rate of blood glucose absorption level after food ingestion [5, 87]. GI ranks carbohydrate-containing food based on their blood glucose level effect. The postprandial glycaemic responses of carbohydrate-rich food and meals potion vary widely. Therefore, food is categorised according to their postprandial glycaemic responses with guidance of GI values [87]. Food can be grouped into three GI categories, namely, low GI (≤55), medium GI (55–69), and high GI (≥70).

Food that is categorised as a low GI usually contains a low concentration of soluble sugars but with a high concentration of unavailable carbohydrates [88]. According to Truswell [89], a low GI characteristic of food is usually linked to the RS content. Food with high RS content has more resistance to carbohydrate digestion and hence lower glucose absorption to prevent extreme blood glucose fluctuations, thus lowering the glycaemic level [87, 90]. Moreover, food that contain slow-digesting carbohydrates have influence on prolonged satiating effects, as these types of food are more satisfying and satiety and thus increase the time elapsed between meals. Food with high amount of RS could be qualified as functional food and have high market opportunities. On the other hand, readily digestible carbohydrates could accelerate the elevated blood glucose level and insulin secretion, which directly lead to various health complications [91].

Plantain flour has market potential due to its favourable characteristic of being able to lower the GI of food then release glucose at a slower rate than high-GI food. This feature is to be useful in the innovation of healthy diets for diabetic and obese individuals. Agama-Acevedo et al. [92] found that low estimated glycaemic index (EGI) cookies can be produced by substituting unripe banana flour for wheat flour. Food produced by incorporating high level of RS is one of the ways to lower the GI of food [27, 92]. According to Saifullah et al. [93], noodles made of green banana flour has lower EGI value than control noodles (i.e. noodle made of 100% wheat flour). A research done by Okafor and Ugwu [94] showed that green banana and plantain have high and slow digestible starch with low GI value. This is due to the presence of high content of RS and dietary fibre of unripe plantain [94]. Another study performed by Choo and Aziz [95] showed that noodles prepared by partial incorporation of green banana flour for wheat flour had significantly reduced the EGI level of the noodles.

In addition, low GI rice noodles were developed by Srikaeo and Arranz-Martinez [96] by using fortified rice flour enriched with amylose and resistant starch. Another research conducted by Srikaeo and Sangkhiaw [97] found that GI value of the rice noodles could be lowered to 51.84 (low GI food) by replacing tapioca starch with high amylose maize starch at 60% level in processing of rice noodles.

Native breadfruit starches contain 2.99% of SDS and 8.42% of RS [80]. Since breadfruit contains an appreciable amount of RS that could lower the glycaemic and insulinemic responses, there is a growing interest towards the utilisation of breadfruit in a wide range of products. Noor et al. [98] reported that breadfruit flour had higher crude fibre of 4.85% than commercial wheat flour, which contained 0.23% crude fibre. According to Zakaria et al. [99], the 5% substitution of breadfruit RS in bread formulation gave a lower GI value of 76 than GI value of 97 showed by control bread. A study from Widanagamage et al. [100] also reported a significant lower GI value of 64 for breadfruit when white bread was used as a standard food for comparison. By using 100% of glucose as a standard food for comparison, boiled breadfruit showed a GI value of 47 [101]. Based on compiled studies, Turi et al. [102] suggested that cooked breadfruit has low to moderate GI which is a potential to be used in controlling diabetes.

#### **5. Effects of resistant starch fortification on food quality**

Fortification of RS to food can provide alternative ways to fill in the gap between the current RS intake and recommended intake amounts. In parallel, consumer

#### *Resistant Starch from Exotic Fruit and Its Functional Properties: A Review of Recent Research DOI: http://dx.doi.org/10.5772/intechopen.88816*

demand for healthy food has grown significantly during the last few decades, whereby preference is given to food that contain RS due to its health benefits. This attention has created a good investment opportunity for food manufacturers to incorporate RS into a wide variety of food products, such as bakery products, dairy products, noodles, and pasta. However, manufacturers need to be wise about the RS types and amounts fortified to their products because adding RS to food creates alteration to the product formulation and can adversely affect the quality of many processed products, such as breads and other bakery products, pasta, and other extruded products.

RS can be used as a functional food ingredient for producing different food products to improve their nutritional value by increasing the fibre-like fraction. From the industrial point of view, RS has a low calorie profile and can be used as a bulking agent in reduced sugar or reduced fat food formulations. RS does not compete for the water needed by other ingredients as it significantly holds less water than traditional dietary fibre and allows easier processing because it does not contribute to stickiness. This may be advantageous in low moisture product productions, such as cookies and crackers. In most applications, it does not alter the taste, texture, or appearance of the food [3]. Moreover, according to Sajilata et al. [21], food products supplemented with RS has no negative effect on the texture or taste of the end product. These food products have received greater consumer acceptability and better palatability than food products supplemented with dietary fibres.

According to Nimsung et al. [103], a substantial percentage of RS present in bananas has capability to promote significant health benefits to food products. Several reported studies showed that an increase in RS content of food products (e.g. pasta, bread, and cookies) that was incorporated with unripe banana [35, 93, 104]. A research done by Juárez-García et al. [35] indicated that green banana flour contained high total starch (73.4%), in which RS represented 17.5%. Several studies demonstrated that the RS content of food products (i.e. noodles, spaghetti, pasta, and cookies) could be improved by the substitution of green banana and unripe plantain [92, 93, 95, 104].

According to Amaral et al. [18], it is technically possible to increase the RS amounts in food. The study investigated factors, such as formulation, loaf size, baking conditions, and storage conditions (i.e. time and temperature), that might affect the formation of RS in wheat bread. Findings indicated that RS content of wheat breads was enhanced by a higher level of moisture in the dough and a larger loaf size of the final product. An extended baking process also increased the RS formation. Storing bread at room temperature for 3 days demonstrated further enhancement of the RS content. Moreover, the RS content of wheat bread could be increased by manipulating the ratio of ingredients and processing time [18]. Studies performed by Sankhon et al. [6] showed that there was improvement in bread RS content as lower temperatures, and longer baking times were applied.

A recent research article [105] reported the substitution of RS for bread flour at 10% without detrimental effect on bread qualities. However it caused lighter crumb colour and lowered the specific volume when higher substitution levels (20 and 30%) of RS were in bread formulation for bread making. In addition, at 30% substitution level, the microstructure of crumbs showed less structural integrity and a coarser network structure [105]. The bread loaves containing RS presented harder bread crumb than the bread without RS substitution [105]. These obtained results were not in line with the reports from Korus et al. [106], whereby the study found that the crumb hardness was reduced with increase in the amount of RS in bread. Besides, the total dietary fibre of bread with RS was also found to increase to 89% as compared to bread without RS (control) [106].

#### *Chemical Properties of Starch*

Jiamjariyatam [49] studied on the effect of the blends between wheat flour and jackfruit seed starch on the physical and chemical properties of batter coating. It was found that the amount of oil absorption in the battered product significantly decreased with increase in jackfruit seed starch in the mixture. Higher jackfruit seed starch content in the batter provided greater homogeneity with a fine starch network and less porosity. In terms of sensory evaluation, adding jackfruit seeds starch in batter coating results in increased hardness and crispness, but decreased brittleness, puffiness, oiliness, and oil coating. The study concluded that the ratio of 50:50 (wheat flour:jackfruit seed starch) in batter coating system gave the highest score in overall preference [49].

Utilisation of jackfruit seed starch as a thickener and stabiliser in chilli sauce was successfully developed by Rengsutthi and Charoenrein [44]. Findings showed that the jackfruit seed starch was suitable as a thickener and stabiliser in chilli sauce because the chilli sauce with jackfruit seeds starch had the lowest serum separation and highest viscosity during storage at 37°C for 4 weeks [44]. Moreover, research by Rengsutthi and Charoenrein [44] showed that the jackfruit seed starch can be a useful stabiliser in a high acid sauce.

Pasta with lower glycaemic response was developed by adding different types of RS [107]. Findings indicated that the addition of resistant starches influenced the quality of both the raw and cooked pastas but had no effect on cooking quality (i.e. water absorption, cooking loss, swelling index, and dry matter) and sensory characteristics of pastas. On the other hand, a study on instant noodles showed that steaming followed by frying of noodle strands resulted in a slight increase in RS content at approximately 1.2 times. In addition, storage of instant noodles for 60 days at room temperature (~25°C) showed a significant increase in RS content by 1.4 times. Therefore, storage could help in RS formation [90].

#### **6. Conclusion and perspectives**

Resistant starch is one of the functional ingredients that is receiving attention due to its unique functional properties and potential physiological benefits. Different digestibility rates of food after ingestion are usually related to various physiological functions, and thus it causes different health effects, such as lowering the glycaemic and insulinemic responses to food, hypocholesterolemic action, and protective effect against colorectal cancer. Food products fortified with RS are becoming popular among consumers who are even ready to pay more for products enriched with RS to increase their dietary fibre intake.

The presence of RS in food is generally low, and it is determined by the starch botanical source, the condition of processing, and storage. The formation of RS during processing of carbohydrate-rich food is influenced by a few factors including moisture content, heating time and temperature, number of heating and cooling cycles, pH, freezing, and drying. RS type 3 is stable to thermal and often used as a functional ingredient in a wide variety of food products. Due to the good functional properties of RS, with no negative effects on the texture and taste of the end product, it is often incorporated into food products. Food products supplemented with RS has more palatability and greater consumer acceptability in terms of taste and colour than those of food products added with functional ingredients that are associated with high fibre content.

Exploiting fruits as well as its by-products, such as seeds, trunk, and peel, provides opportunity in its use as a natural resource of functional food ingredient in preparing value-added products. Therefore, this can benefit both local farmers and food as well as pharmaceutical industries. But associated drawbacks are

*Resistant Starch from Exotic Fruit and Its Functional Properties: A Review of Recent Research DOI: http://dx.doi.org/10.5772/intechopen.88816*

related to consumer acceptability and processing/extraction cost concerns. Based on the information recorded in this review, it is expected that more botanical sources can be exploited for their potential as functional food ingredients (i.e. RS), including more food products fortified with RS that can be developed for local and international markets. Therefore, researchers and nutritionists should work together on RS production from different botanical sources as well as the application of this processed RS in the development of carbohydrate-based functional foods with low GI.

#### **Acknowledgements**

The authors wish to thank Universiti Sultan Zainal Abidin for the financial support from the University Research Grant under the Lab Material (LABMAT) 2018 grant (UniSZA/LABMAT/2018/02; R0044-R002).

#### **Conflict of interest**

All authors declare there is no conflict of interest in this review.

#### **Notes**

This review is submitted in partial fulfilment of the requirements for the LABMAT 2018 grant (UniSZA/LABMAT/2018/02; R0044-R002) publication.

#### **Author details**

Lee-Hoon Ho\* and Shi-Yun Wong Department of Food Industry, Faculty of Bioresources and Food Industry, Universiti Sultan Zainal Abidin, Besut, Terengganu, Malaysia

\*Address all correspondence to: holeehoon@yahoo.com; holeehoon@unisza.edu.my

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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### **Chapter 8**

## Resistant Starch

*William Russell Sullivan*

#### **Abstract**

Not all starch that is ingested into the human body is digested into D-glucose – the portion that defies this process is referred to as resistant starch (RS) where chemically and mechanically, five different forms have been identified. Regardless of the form, an extensive breadth of health benefits has been associated with the consumption of RS. These include the potential of RS becoming part of weight and diabetes management plans as well as improved colon health and prevention of colon cancer. Therefore, in the past decade, there has been a significant amount of research into how RS concentrations can be increased in various food systems, which have had varying degrees of success; however, are limited to either enzymatic, thermal, or acidic alterations to starch. In a similar fashion, chemical methods of RS measurement have also received a considerable amount of change and enhancement over time, though with most of them to some extent attempting to replicate human carbohydrate digestion.

**Keywords:** resistant starch, crystallinity, butanoic acid, health benefits, digestion, glycemic index

#### **1. Introduction**

Resistant starch could be the next "super food," its wide range of health benefits make it a very appealing ingredient in food formulations. It was first discovered in the early 1980s and since then large amounts of research have been devoted to RS and its applications in the food industry. The objectives of this chapter are to introduce and explain the different types of RS, identify the wide range of health benefits associated with the consumption of RS as well as the current mechanisms of increasing RS concentrations.

#### **2. Starch digestion**

The digestion of starches (carbohydrates) begins as soon as the food product enters the oral cavity where the act of chewing (mastication) breaks down the chunks of food into smaller particles [1]. These particles have a larger surface area to volume ratio allowing an effective and penetrating coating of saliva, secreted by the salivary glands in a response to chewing. Saliva (pH 6.8), while mostly water, is approximately 1% a combination of electrolytes and enzymes [1]. One of these enzymes is a digestive protein known as α-amylase, which initiates starch hydrolysis by randomly cleaving the α(1 → 4) linkages found in starch [2].

Once the food is of a small enough size and sufficiently coated in saliva, it is then swallowed and passes through into the stomach via the pharynx and esophagus.

#### *Chemical Properties of Starch*

The environment of the stomach has a very low pH, around 1.0, due to the presence of hydrochloric acid (HCl). This low pH environment deactivates the α-amylase introduced in the mouth and as such no further carbohydrate digestion occurs in the stomach [3]. Other digestive enzymes including proteases and lipases are introduced initiating the degradation of proteins and lipids [4].

From the stomach, this mixture of acid, enzymes and partially digested food (known as chyme) enters the first section of the small intestine call the duodenum. Here, secretions from the pancreas and the gall bladder raise the pH up to around 7.8 allowing further α-amylase to be introduced from the epithelial cell walls lining the small intestine. The breakdown (hydrolysis) of starch therefore continues in the small intestine creating shorter and shorter chains of carbohydrates with varying lengths until maltose or dextrins are reached. **Figure 1** showcases the pathway that is carbohydrate digestion. Maltase, another pancreatic enzyme is introduced to

#### *Resistant Starch DOI: http://dx.doi.org/10.5772/intechopen.90159*

cleave the α(1 → 4) linkage of maltose as α-amylase cannot complete this process. α-amylase cannot break α(1 → 4) linkages if they are near or adjacent to already cleaved bonds, hence the requirement for the additional enzyme, maltase [3, 5]. Once glucose is produced, monosaccharide is absorbed through the wall of the small intestine into the bloodstream via a number of complex pathways.

The extent and rate of carbohydrate digestion in the human body is highly dependent upon the chain length as it is ingested, hence, the number of glycosidic bonds present and their form. Small structured carbohydrates like maltose, glucose and fructose often present in sweet foods like confectionary and fruits are digested and absorbed relatively quickly as little or no enzymatic digestion is required [6]. Larger, more complex carbohydrates on the other hand such as oligosaccharides and starch can take a significantly longer time to digest – based on this information, starches can be classified into three main forms based on their rate of digestibility [7]:


RDS is strongly correlated with high glycemic index foods as it is mainly amorphous starch that may have been either completely or partially gelatinized. These include baked goods likes white breads and cookies that are digested fairly quickly, in less than 20 min [6]. SDS is frequently found in weight loss and healthy eating programs as digestion takes significantly longer, between 20 and 110 min. The result of this is a more consistent and controlled release of glucose into the bloodstream over a longer period of time, which also has an impact on sustained satiety (feeling of "fullness") [7].

### **3. Resistant starch**

The term resistant starch (RS) was first coined by Englyst et al. in 1982 [8]. RS as a definition refers to the proportion of starch that is ingested though is not digested by human enzymes. This portion of starch therefore passes through the small intestine into the colon undigested, where it has been shown to act as a carbon substrate for beneficial bacteria, making RS a form of dietary fiber. At present, five different forms of RS have been classified (RS1 – RS5) grouped based on how they are resistant to digestion (**Table 1**).

RS1 is best described as physically inaccessible starch as a physical barrier is present which prevents enzymes from gaining access to the starch. This barrier is often a plant cell wall where RS1 is frequently found in grains and millet seeds [9]. R2S is commonly referred to as raw starch, or, native starch where the starch granule is completely intact and as such has undergone no form of pressure or thermal processing. Native forms of starch typically have higher degrees of crystallinity resulting in this resistant nature [9].

In comparison, RS3 has intentionally undergone a process of gelatinization and retrogradation (recrystallization) which is usually done hydrothermally. This heating process with subsequent cooling, allows additional starch to crystallize and hence RS to form. RS3 has a number of applications in food manufacturing as it has the ability to form during food processing, unlike both RS1 and RS2 [6]. RS3 is formed most efficiently when the amylose portion of the starch is higher than


**Table 1.**

*Different forms of resistant starch with common food sources.*

usual, allowing for efficient packing and stacking upon cooling. RS4 has reduced digestibility through chemical modification including etherization, esterification, or cross-linking. Finally, RS5 has only recently appeared in literature over the past 5 years and forms when the amylose portion of the starch complexes with a lipid, such as a free fatty acid to form a helical structure [10].

With ongoing research it would not be surprising if additional forms of RS are indeed discovered and this current classification of RS be altered or revisited in the future. Usually, in most staple, day to day foods, the RS content of foods is low (<2%), which has been one of the main driving factors in the increase in research over the last decade investigating methods of how to increase this.

#### **4. Health benefits**

It is clear that the consumption of RS is positively associated with large and broad range of health benefits in disease prevention as well as treatment, often working complimentary. Briefly, in this section of the chapter, some of the more researched and significant health benefits of RS to date will be discussed, while it is noted that this is very much an active and broad research area [11].

A number of the health benefits associated with RS can be explained by microbial fermentation within the human colon, making RS a prebiotic. In order for a substance to be classified as a prebiotic, it must [12]:

1. resist digestion from both enzymes and acid produced by mammals


#### **4.1 Short-chain fatty acids**

Through fermentation in the large intestine, a range of short-chain fatty acids (SCFAs) are produced. The SCFAs are manufactured in varying quantities where it largely depends on the type of bacterium and the source of starch though almost always include a combination of acetic (usually the largest amount), propionoic, lactic, and butanoic acids [13]. As a synergistic combination, these acids assist in maintaining the low pH environment of the colon preventing the growth of pathogenic bacteria and enhancing the proliferation of beneficial, probiotic strains.

**Figure 2.** *The molecular structure of butanoic acid.*

Butanoic acid (**Figure 2**) in particular has been shown to demonstrate a range of other health benefits including acting as a preferred carbon source for the cells of the colon (colonocytes). This improves the overall health of the colon by enhancing the strength of the epithelial layer, increasing blood flow, and reducing inflammation [14]. Several other studies have also found that increased quantities of butanoic acid may also be linked with a reduced risk of colon cancer. Butanoic acid has been shown to limit the growth of abnormal, fast growing tumor cells by stopping the G1 phase in cell replication [12]. Colon health is also enhanced by the ability of RS to hold water which increases defecation rates which in turn decreases the accumulation of mutagenic compounds.

#### **4.2 Glycemic effects**

Foods that have large amounts of RS are digested at a much slower rate when compared to similar foods containing larger concentrations of either SDS or RDS [15]. The effects of these slower digestive processes can be observed in human and animal test subjects with the measurement of blood glucose levels and subsequent insulin responses at different time periods post ingestion. It has been shown and would be expected that foods high in RS would be associated with low glycemic index foods [12]. Therefore, RS has the potential to become part of treatment plans and management programs for weight loss as well as diabetes type two [6].

MacNeil et al. [16] conducted a study where humans suffering from type two diabetes consumed baegels that were supplemented with varying amounts of RS2. Interestingly, when the RS replaced a portion of the total wheat flour, a reduction in postprandial glucose and insulin levels were observed. Although, when the RS2 was added in addition to the wheat flour these reductions were not seen – a phenomenon also observed by Luhovyy et al. [17] in cookies. Behall and Hallfrisch [18] facilitated the formation of RS3 by adding high amounts of amylose into bread formulations finding that when the amylose content made up 50% of the formation, significant reductions in postprandial glucose and insulin were observed – which was attributed to the straight chained nature of amylose, allowing for efficient stacking and hence crystallization upon cooling.

Evidence is also present to suggest that the consumption of RS can affect the regulation of satiety hormones including glucagon-like-peptide-1 (GPL-1) and peptide YY (PYY). Both hormones play a role in the stimulation of insulin secretion and facilitate a feeling of satiety through the central nervous system, working synergistically with leptin [15]. Zhou et al. [19] and Hoffmann [20] conducted similar studies measuring hormone levels after an increased intake of RS and saw increases in both GLP-1 and PYY while Hoffmann [20] additionally saw a decrease in levels of ghrelin.

It is evident that RS has the potential to have a multi-tiered approach when it comes to the management of weight as well as carbohydrate related conditions including diabetes, in addition to all of the secondary diseases that are commonly

#### *Chemical Properties of Starch*

associated with obesity. RS therefore has significant potential from a health point of view to be incorporated into various food systems not only from a glycemic perspective but a lower bowel health perspective as well.

#### **5. Increasing resistant starch concentrations**

Given the range of health benefits that are associated with the consumption of RS, a great deal of research has been conducted around how concentrations can be increased in various food systems. In this chapter, we will focus on three main methods of achieving this, with, heat, enzymes and acid.

#### **5.1 Thermal treatments**

It was mentioned briefly at the start of this chapter that RS3 has a number of applications due to its ability to form during food processing. This is typically best achieved with starches that have higher percentages of amylose, the straight chained form of starch as when the starch is cooled, they have a higher ability and chance to stack together and hence crystallize via hydrogen bonding, compared to that of amylopectin [21]. Indeed, some of the most positive results have come from when researches that have exposed starch to a number of hydrothermal cycles, that is, heating and cooling at pre-determined temperatures and times, more than once [22]. For instance, Liu et al., [23], exposed buckwheat and sorghum starches to annealing and saw buckwheat RS increase from 3.3 to 4.8% and from 3.5 to 4.2 for sorghum. As expected, they also say an inverse relationship between RS and RDS – as RS increased, the RDS proportion decreased.

#### **5.2 Enzymatic treatments**

Debranching enzymes such as isoamylase and pullulanase are capable of cleaving the α(1 → 6)bonds, commonly found in amylopectin and amylose to a smaller extent. By cleaving these branching points, the result are more straight chained forms of starch, similar to that of amylose – increasing RS concentrations in the same mechanism mentioned previously regarding thermal treatments [24]. Pullulanase in-particular, has received a considerable amount of recent research [24–26]. Shi et al. [26] studied investigated the effects of varying pullulanase concentrations on the digestion of waxy (high amylopectin content) maize starch. The native maize starch possessed an RS concentration of 1.2% while after an exposure to a pullulanase concentration at 20 enzyme U/g, produced a dramatic increase to 37.7% RS. They also saw an increase in the apparent amylose content, which would be expected as the sample, which in its native form is nearly 100% amylopectin, begins to have its α(1 → 6)bonds cleaved. Interestingly, they also found a crystalline shift after the enzymatic and thermal treatment, where the maize moved from having an A-type crystal to having a combination of both B-type and V-type. The V-type, as measured with X-ray diffraction, refers to a complexation of amylose with a lipid, otherwise known as RS5 [10], though while still a form of resistant starch, this would indeed hinder the formation of the intended RS3.

#### **5.3 Acidic treatments**

The action of acidic on RS formation appears to have a very similar mechanism to that of the debranching enzymes – the ability of a low pH environment to hydrolyse glycosidic linkages increasing the crystalline forming capability. At this point, treating starches with acid appears to be the most ineffective method of increasing RS concentration, when compared to hydrothermal or enzymatic exposure rounds.

#### *Resistant Starch DOI: http://dx.doi.org/10.5772/intechopen.90159*

Acid hydrolysis has been observed in various starches using scanning electron microscopy, where pores form on the outside of the starch granule after an extended exposure. These pores would then act as an access point for hydronium ions to enter the granule, reducing the proportion of amorphous starch present [27]. However, this does not appear to be the case with all starches, with Miao et al. [28] finding that the RS concentrations in maize starch first decreased before increasing with time of exposure, though increases were negligible.

### **6. Measurement of resistant starch**

An effective means of measuring RS has proven to be a complex task, where a number of both *in-vivo* and *in-vitro* methods have been developed since the early 1980's, with many iterations and alterations since then. A great deal of development was done during the mid-1990s, one of which was by Englyst, Kingman and Cummings [29] in 1992, that effectively separated RDS, SDS, and RS. A method that is still commonly used to gain a broader understanding of digesting [24, 30], often relating to glycemic index studies. The design of this measurement model was to replicate human digestion using a range of additives such as proteases, HCl and guar gum to replicate the stomach. Starch digestion is achieved with an enzyme mixture of invertase, heat stable α-amylase, pullulanase, pancreatin and amyloglucosidase (AMG) where aliquots are taken at different time periods of digestion. Aliquots from 20 min represent RDS, while 120 min of digestion refer to SDS and anything left after 240 min is defined as RS. Glucose concentrations are determined using glucose oxidase and the starch contents are calculated using the following equations:

RDS (%) = (G20 <sup>−</sup> FG) <sup>×</sup> 0.9 \_\_\_\_\_\_\_\_\_\_\_\_\_ TS SDS (%) = (G120 <sup>−</sup> G20) <sup>×</sup> 0.9 \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ TS RS (%) = TS − (RDS <sup>+</sup> SDS) \_\_\_\_\_\_\_\_\_\_\_\_\_\_ TS

One of the more commonly used methods nowadays was developed by McLeary and Monaghan [31] in 2002 and was the result of a comparative study between the different methods used at the time to measure RS in food systems. McLeary and Monaghan [31] experimented with a range of factors, including:


In this method (AOAC Method 2002.02/AACC 32–40.01) 100 mg samples of the food are weighed out and exposed to an enzyme cocktail of both AMG and α-amylase for 16 h at exactly 37°C. In this step, the non-resistant starch is hydrolysed to glucose, before the reaction is then halted with the addition of ethanol in a repeated washing process. If the researcher requires to measure total starch content so, they can now

#### *Chemical Properties of Starch*

take aliquots from the ethanol for subsequent quantification and addition to resistant starch contents. After the ethanol washing, a pellet contain the RS is obtained at the bottom of the centrifuge tube. The RS is dissolved with agitation over an iced bath with the addition of KOH before introducing AMG for the final time, to hydrolyse the remaining starch into D-glucose. Subsequently, the RS and total starch contents can be determined with the glucose oxidase peroxidase (GOPOD) reagent.

Clearly, the different methods of RS measurement in foods are complex and have the potential for a great deal of variability if users are not trained adequately. In addition, they can also be rather time intensive and expensive. The methods described here are by no means all of the methods researched – for a greater discussion on the topic, the reader is referred to Berry in 1986 [32], Bjork in 1986 [33] and Champ in 1992 [34].

#### **7. Conclusions**

In conclusion, it is clear that resistant starch has a large amount of potential to be incorporated into food systems in order to convey a wide range of health benefits from reducing the risk of colon cancer to managing weight loss and diabetes type two. A range of methods have been in trial in attempts to increase RS concentrations in from various sources of starch, including thermal, enzymatic and acidic treatments. Great success has been observed when a holistic approach has been adopted, manipulating each factor to optimize RS formation, rather than depending on one method individually. A great deal of future research lies in this area of optimizing RS concentrations at an economical level, as enzymatic treatments can add significant financial costs when done on a large scale.

#### **Author details**

William Russell Sullivan

School of Science, Bioscience and Food Technology Discipline, RMIT University, Melbourne, Victoria, Australia

\*Address all correspondence to: william.sullivan@rmit.edu.au

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Section 4
