1. Introduction

Pectin is a structural polysaccharide found in all higher plant fruits as citrus, apples, grapes, plums, etc. and is, therefore, part of the natural man diet. Many aspects of plant physiology and pathology, food texture, and even wine production involve pectin and its fate in materials and organisms. Commercial preparations of pectin are usually derived from citrus or apple peels, by-products of juice manufacture. The production involves aqueous extraction under mild acidic conditions, followed by precipitation by the addition of a di- or trivalent metal alcohol or ions.

Most of the world production of pectin is used for the preparation of jams and jellies, but a growing part is used in confectionery products, beverages, and acidified milk drinks. Pectin is suitable for applications in acidic food products due to its good stability at low pH values [1]. For this same reason, it is currently also used in the pharmaceutical industry as in the manufacture of capsules, films, and biodegradable patches.

1.2 Rhamnogalacturonan-I (RGI)

DOI: http://dx.doi.org/10.5772/intechopen.88944

1.3 Rhamnogalacturonan-II (RGII)

Ara in Gal C3 [2].

GalU linked in α (1 ! 4) with L-rhamnose (Rha) residues intercalated with an α (1-2) bond, that is, [(1-2)-α-L-Rha-(1-4)-α-D-GalU] n, where n can be greater than 100. These Rha residues are the anchoring of side chains, and approximately half are bound by C4 to chains of arabinans, formed by α-L-arabinose (Ara) linked in α (1 ! 5) as the main axis that can be substituted with the chains Ara (1-2)-α-Ara (1-3) and/or Ara (1-3)-α-Ara (1-3) or arabinogalactan I (AGI), chains of β-(1-4)- D-galactose (Gal), with C6-Gal branches. They can also be substituted for α (1 ! 5)

Small polysaccharide of very complex structure, formed by GalU, Rha, Ara, Gal,

Arabinans and galactans of the RGII of the Amaranthaceae family can be associated to ferulic acid through an ester bond, which makes it possible to link several chains by diferulic bridges, through the action of the peroxidases. Links are also caused by the dimerization of hydroxycinnamic acids linked to arabinans and

Commercial pectins are derived almost exclusively from citrus or apple, both by-products of the manufacture of juice or cider. While the apple pomace contains 10–15% pectin on a dry matter basis, the citrus peel contains 20–30%. The pectin of citrus fruits and apples is equivalent from the point of view of the application. However, citrus pectins are light cream or light tan; apple pectins are often darker. Other suggested alternative sources include sugar beet residues, sunflower heads (seeds used for edible oil), and mango residues. The pectin from sugar beet was produced in Germany during World War II and in Sweden and Russia in the following years. The beet pectin is inferior to the citric pectin in molecular weight. All currently significant applications are related to (1) the degree of acetate esterification, (2) relatively low molecular mass, and (3) the presence of large

The use of pectin in traditional sugar jams is one of the best known applications, being one of the largest pectin markets. Very often the pectin is the only gelling agent allowed, with 0.2–0.4% of pectin, depending on the type and origin of the fruit. Within the European Economic Community, there are two standards in jam and extra marmalade, which contain a minimum of 30 or 45% fruit pulp, respectively. The higher quality of jam also tends to be made with better quality fruit, so it

The jam of citrus fruit, especially lemon or grapefruit, in which pectin has been produced in a higher than normal content, generates disadvantages. In this case, too much pectin in the fruit leads to too strong gel formation or even to pregelation and syneresis; the attempt to regulate the texture with the pH leads to a situation in which the control is extremely critical and the rejection rate to this pectin is inevitable. One solution has been to work at a pH where the pectin in the fruit no longer forms a gel. The gelation can then be achieved by adding a pectin-amide of low

and small amounts of infrequent sugars such as apiose or acetic acid. The Rha moieties may be substituted at C3; in C3 and C4, in C2, C3, and C4 or be terminal. The arabinogalactan of the RGII presents ramifications in C3 and C6 of Gal and in C3 and C5 of Ara. The side chains contain a high number of different residues bound with various bonds. However, the RGII has a highly conserved structure and

can form dimers via a borate bridge, with two ester bonds [2].

Extraction and Characterization of Pectins From Peels of Criolla Oranges…

galactans of the RGI due to the action of peroxidases [2, 3].

methoxyl content which is capable of gelling at high pH [4].

amounts of neutral sugar side chains [4].

requires significantly less pectin.

5

Pectins are complex heterogeneous polysaccharides; it is used plurally because it differs from its composition from one species to another (the pectin obtained from a citrus differs, e.g., from the apple; even within citrus, there are small differences). Like most other vegetable polysaccharides, it is both polydispersed and polymolecular, and its composition varies with the source and conditions applied during storage. In any pectin sample, parameters such as weight or content of particular subunits will differ from molecule to final molecule.

All pectin molecules contain linear segments of α (1 ! 4)-D-galactopyranosyl uronic acid units linked with some of the carboxyl groups esterified with methanol (Figure 1). In the pectin of some sources, some of the hydroxyl groups of the galacturonosyl units (0–2 and/or 0–3, oxygen bonded to carbon 3) are esterified with acetic acid [2].

Pectins are a mixture of acidic and neutral branched polymers. They constitute 15–30% of the dry weight of the primary wall of plant cells. They determine the porosity of the wall and therefore the degree of availability of the substrates of the enzymes involved in the modifications of the same. Pectins also provide charged surfaces that regulate pH and ion balance. In the presence of water, they form gels. Pectins have three main domains:

#### 1.1 Homogalacturonans (HG)

Compounds by D-galacturonic acid (GalU) residues are bound by an α (1 ! 4) bond. The carboxyl groups of C6 (carbon number 6 of the GalU) can be methyl esterified or remain free. The free carboxyl groups, if dissociated, give rise to calcium bonds between the neighboring HG chains, forming the so-called egg box structure. For a region of HG to be sensitive to calcium binding, 10 molecules of unesterified GalU are required, the formation of bonds of this type is related to the arrest of the cell wall and, therefore, with the cessation of growth and increase of stiffness of the wall. The GalU can be found acetylated in O2 (oxygen number 2 of the GalU) or in O3 [2].

Figure 1. Basic chemical structure of α (1 ! 4)-D-polygalactopyranosyl uronic acid.

Extraction and Characterization of Pectins From Peels of Criolla Oranges… DOI: http://dx.doi.org/10.5772/intechopen.88944

#### 1.2 Rhamnogalacturonan-I (RGI)

Most of the world production of pectin is used for the preparation of jams and jellies, but a growing part is used in confectionery products, beverages, and acidified milk drinks. Pectin is suitable for applications in acidic food products due to its good stability at low pH values [1]. For this same reason, it is currently also used in the pharmaceutical industry as in the manufacture of capsules, films, and biode-

Pectins are complex heterogeneous polysaccharides; it is used plurally because it differs from its composition from one species to another (the pectin obtained from a citrus differs, e.g., from the apple; even within citrus, there are small differences).

polymolecular, and its composition varies with the source and conditions applied during storage. In any pectin sample, parameters such as weight or content of

All pectin molecules contain linear segments of α (1 ! 4)-D-galactopyranosyl uronic acid units linked with some of the carboxyl groups esterified with methanol (Figure 1). In the pectin of some sources, some of the hydroxyl groups of the galacturonosyl units (0–2 and/or 0–3, oxygen bonded to carbon 3) are esterified

Pectins are a mixture of acidic and neutral branched polymers. They constitute 15–30% of the dry weight of the primary wall of plant cells. They determine the porosity of the wall and therefore the degree of availability of the substrates of the enzymes involved in the modifications of the same. Pectins also provide charged surfaces that regulate pH and ion balance. In the presence of water, they form gels.

Compounds by D-galacturonic acid (GalU) residues are bound by an α (1 ! 4) bond. The carboxyl groups of C6 (carbon number 6 of the GalU) can be methyl esterified or remain free. The free carboxyl groups, if dissociated, give rise to calcium bonds between the neighboring HG chains, forming the so-called egg box structure. For a region of HG to be sensitive to calcium binding, 10 molecules of unesterified GalU are required, the formation of bonds of this type is related to the arrest of the cell wall and, therefore, with the cessation of growth and increase of stiffness of the wall. The GalU can be found acetylated in O2 (oxygen number 2 of

Like most other vegetable polysaccharides, it is both polydispersed and

particular subunits will differ from molecule to final molecule.

Pectins - Extraction, Purification, Characterization and Applications

Basic chemical structure of α (1 ! 4)-D-polygalactopyranosyl uronic acid.

gradable patches.

with acetic acid [2].

Pectins have three main domains:

1.1 Homogalacturonans (HG)

the GalU) or in O3 [2].

Figure 1.

4

GalU linked in α (1 ! 4) with L-rhamnose (Rha) residues intercalated with an α (1-2) bond, that is, [(1-2)-α-L-Rha-(1-4)-α-D-GalU] n, where n can be greater than 100. These Rha residues are the anchoring of side chains, and approximately half are bound by C4 to chains of arabinans, formed by α-L-arabinose (Ara) linked in α (1 ! 5) as the main axis that can be substituted with the chains Ara (1-2)-α-Ara (1-3) and/or Ara (1-3)-α-Ara (1-3) or arabinogalactan I (AGI), chains of β-(1-4)- D-galactose (Gal), with C6-Gal branches. They can also be substituted for α (1 ! 5) Ara in Gal C3 [2].

#### 1.3 Rhamnogalacturonan-II (RGII)

Small polysaccharide of very complex structure, formed by GalU, Rha, Ara, Gal, and small amounts of infrequent sugars such as apiose or acetic acid. The Rha moieties may be substituted at C3; in C3 and C4, in C2, C3, and C4 or be terminal. The arabinogalactan of the RGII presents ramifications in C3 and C6 of Gal and in C3 and C5 of Ara. The side chains contain a high number of different residues bound with various bonds. However, the RGII has a highly conserved structure and can form dimers via a borate bridge, with two ester bonds [2].

Arabinans and galactans of the RGII of the Amaranthaceae family can be associated to ferulic acid through an ester bond, which makes it possible to link several chains by diferulic bridges, through the action of the peroxidases. Links are also caused by the dimerization of hydroxycinnamic acids linked to arabinans and galactans of the RGI due to the action of peroxidases [2, 3].

Commercial pectins are derived almost exclusively from citrus or apple, both by-products of the manufacture of juice or cider. While the apple pomace contains 10–15% pectin on a dry matter basis, the citrus peel contains 20–30%. The pectin of citrus fruits and apples is equivalent from the point of view of the application. However, citrus pectins are light cream or light tan; apple pectins are often darker.

Other suggested alternative sources include sugar beet residues, sunflower heads (seeds used for edible oil), and mango residues. The pectin from sugar beet was produced in Germany during World War II and in Sweden and Russia in the following years. The beet pectin is inferior to the citric pectin in molecular weight.

All currently significant applications are related to (1) the degree of acetate esterification, (2) relatively low molecular mass, and (3) the presence of large amounts of neutral sugar side chains [4].

The use of pectin in traditional sugar jams is one of the best known applications, being one of the largest pectin markets. Very often the pectin is the only gelling agent allowed, with 0.2–0.4% of pectin, depending on the type and origin of the fruit. Within the European Economic Community, there are two standards in jam and extra marmalade, which contain a minimum of 30 or 45% fruit pulp, respectively. The higher quality of jam also tends to be made with better quality fruit, so it requires significantly less pectin.

The jam of citrus fruit, especially lemon or grapefruit, in which pectin has been produced in a higher than normal content, generates disadvantages. In this case, too much pectin in the fruit leads to too strong gel formation or even to pregelation and syneresis; the attempt to regulate the texture with the pH leads to a situation in which the control is extremely critical and the rejection rate to this pectin is inevitable. One solution has been to work at a pH where the pectin in the fruit no longer forms a gel. The gelation can then be achieved by adding a pectin-amide of low methoxyl content which is capable of gelling at high pH [4].

Both the selection of the correct pectin (the lower the solid solubility, the more sensitive to calcium) and the pectin content in fruit are important. Sometimes, especially at very low amounts of pectin, it may be necessary to add a calcium salt to obtain a better result. From time to time, neutral gums are added to reduce syneresis, but each attempt must be made to optimize the type and level of pectin. The exact pH before considering such addition should be considered, since the gums can mask the delicate taste of these products [4].

Jam makers also manufacture fillings and toppings for the bakery and related industries. Many of these use pectin as a gelling agent or thickener, but, because it depends so much on their processing conditions, it is very difficult to generalize a process on an industrial scale.

In recent years, a growing area of the fruit product industry is the production of fruit for addition to yogurts and similar products. Many of these have been made with modified starch as a thickener to ensure a homogeneous distribution of the fruits together with the texture that must be extruded and the difficulties that this entails. Unfortunately, although starches are relatively inexpensive, they can mask delicate fruit flavors and lead to a mealy texture. These foods have sugar contents between 30 and 60%, so high methoxyl pectin can be used. Pectins have other uses in the dairy industry, for example, the high methoxyl pectin prevents the aggregation of casein in the heating to pH values lower than 4 or 3. It can therefore be used as a stabilizer for the drinkable yogurts treated with UHT and for mixtures of milk and fruit juices. It will also stabilize acidified soy milk drinks and whey products. The yogurt can be thickened by adding very low levels of low pectin in amidated methoxyl before cultivation. Although this is not allowed in many countries, a suitable pectin incorporated in a fruit base can, with careful formulation, have an effect comparable to a fruit yogurt. On the other hand, low-calorie soft drinks are often thin and lack the characteristic mouthfeel provided by sugar in conventional soft drinks. A low level of pectin (usually of controlled viscosity) can be used to improve the texture of these products and also to replace part of the texture due to fruit pulp in juice formulations [5].

#### 1.4 Pectin extraction and purification

For pectin extraction two general processes are used: (1) those that separate pectins from most of the other materials by precipitation with an alcohol and (2) those that precipitate pectins as an insoluble salt with suitable multivalent metal ions (Figure 2). Both can be used to obtain any pectin within the two main groups, namely, high methoxyl pectin (HM-pectin) and low methoxyl pectin (LM-pectin).

The conditions chosen for the extraction depend on the raw material and the desired product. Temperatures between 50 and 90 °C, pH 1-3, and with extraction times from 30 minutes to 24 hours. Acidification can be done with sulfuric acid, sulfurous acid, hydrochloric acid or nitric acid, in accord with reference [4, 5].

is saving alcohol. The concentration is usually done by evaporation, but ultrafiltration has been attempted. Al3+ is usually chosen if the pectin is separated from the extract as an insoluble one. Precipitation by Cu2+ can be an alternative. The metal ions are subsequently removed by several washes with HCl diluted in alcohol [8]. De-esterification to achieve the end of LM-pectin is usually done in an alcohol to which an acid or a base has been added. However, most of all LM-pectin are deesterified with ammonia, thus producing amidated pectin. The traditional alcohol for the manufacture of pectin is 2-propanol (isopropanol), but also methanol or ethanol can be used. The recovery of alcohol by distillation adds considerable

Extraction and Characterization of Pectins From Peels of Criolla Oranges…

DOI: http://dx.doi.org/10.5772/intechopen.88944

A simple process of obtaining pectins is the one observed in Figure 2, in accor-

energy costs to production [4, 9].

Manufacturing process of pectins [4].

dance to Ref. [4].

7

Figure 2.

Processes with a long extraction time, where the pH is low and the temperature is high, are conducive to high product yield, but the quality can be adversely affected. The combination of low temperature with long duration and low pH to obtain some degree of de-esterification (DE) in the extraction in order to produce LM-pectin or on the contrary a slow hydrolysis in time generates HM-pectin [6].

The extraction is followed by filtrations. The raw materials used, which are very soft and swellable, are separated in an initial coarse mesh filtration and sold as livestock feed. The fine suspended solids are subsequently removed from the extract by filtration through diatomaceous earth [7].

If precipitation with alcohol is used to separate the pectin from the extract, the concentration of the extract usually precedes the precipitation, the reason for which Extraction and Characterization of Pectins From Peels of Criolla Oranges… DOI: http://dx.doi.org/10.5772/intechopen.88944

is saving alcohol. The concentration is usually done by evaporation, but ultrafiltration has been attempted. Al3+ is usually chosen if the pectin is separated from the extract as an insoluble one. Precipitation by Cu2+ can be an alternative. The metal ions are subsequently removed by several washes with HCl diluted in alcohol [8].

De-esterification to achieve the end of LM-pectin is usually done in an alcohol to which an acid or a base has been added. However, most of all LM-pectin are deesterified with ammonia, thus producing amidated pectin. The traditional alcohol for the manufacture of pectin is 2-propanol (isopropanol), but also methanol or ethanol can be used. The recovery of alcohol by distillation adds considerable energy costs to production [4, 9].

A simple process of obtaining pectins is the one observed in Figure 2, in accordance to Ref. [4].

Both the selection of the correct pectin (the lower the solid solubility, the more sensitive to calcium) and the pectin content in fruit are important. Sometimes, especially at very low amounts of pectin, it may be necessary to add a calcium salt to obtain a better result. From time to time, neutral gums are added to reduce syneresis, but each attempt must be made to optimize the type and level of pectin. The exact pH before considering such addition should be considered, since the gums can

Jam makers also manufacture fillings and toppings for the bakery and related industries. Many of these use pectin as a gelling agent or thickener, but, because it depends so much on their processing conditions, it is very difficult to generalize a

In recent years, a growing area of the fruit product industry is the production of fruit for addition to yogurts and similar products. Many of these have been made with modified starch as a thickener to ensure a homogeneous distribution of the fruits together with the texture that must be extruded and the difficulties that this entails. Unfortunately, although starches are relatively inexpensive, they can mask delicate fruit flavors and lead to a mealy texture. These foods have sugar contents between 30 and 60%, so high methoxyl pectin can be used. Pectins have other uses in the dairy industry, for example, the high methoxyl pectin prevents the aggregation of casein in the heating to pH values lower than 4 or 3. It can therefore be used as a stabilizer for the drinkable yogurts treated with UHT and for mixtures of milk and fruit juices. It will also stabilize acidified soy milk drinks and whey products. The yogurt can be thickened by adding very low levels of low pectin in amidated methoxyl before cultivation. Although this is not allowed in many countries, a suitable pectin incorporated in a fruit base can, with careful formulation, have an effect comparable to a fruit yogurt. On the other hand, low-calorie soft drinks are often thin and lack the characteristic mouthfeel provided by sugar in conventional soft drinks. A low level of pectin (usually of controlled viscosity) can be used to improve the texture of these products and also to replace part of the texture due to

For pectin extraction two general processes are used: (1) those that separate pectins from most of the other materials by precipitation with an alcohol and (2) those that precipitate pectins as an insoluble salt with suitable multivalent metal ions (Figure 2). Both can be used to obtain any pectin within the two main groups, namely, high methoxyl pectin (HM-pectin) and low methoxyl pectin (LM-pectin). The conditions chosen for the extraction depend on the raw material and the desired product. Temperatures between 50 and 90 °C, pH 1-3, and with extraction times from 30 minutes to 24 hours. Acidification can be done with sulfuric acid, sulfurous acid, hydrochloric acid or nitric acid, in accord with reference [4, 5].

Processes with a long extraction time, where the pH is low and the temperature

is high, are conducive to high product yield, but the quality can be adversely affected. The combination of low temperature with long duration and low pH to obtain some degree of de-esterification (DE) in the extraction in order to produce LM-pectin or on the contrary a slow hydrolysis in time generates HM-pectin [6]. The extraction is followed by filtrations. The raw materials used, which are very

soft and swellable, are separated in an initial coarse mesh filtration and sold as livestock feed. The fine suspended solids are subsequently removed from the

If precipitation with alcohol is used to separate the pectin from the extract, the concentration of the extract usually precedes the precipitation, the reason for which

extract by filtration through diatomaceous earth [7].

6

mask the delicate taste of these products [4].

Pectins - Extraction, Purification, Characterization and Applications

process on an industrial scale.

fruit pulp in juice formulations [5].

1.4 Pectin extraction and purification

#### 1.5 Films

A film is a uniform layer that can be formed either from a single component or from a mixture of polymers. The film development with biodegradable polymers is a promising technology in the food packaging industry. Food packaging is used for the preservation and protection of all types of food and its raw materials, particularly oxidative and microbial deterioration, as well as to extend the shelf life. The increased use of synthetic packaging films has led to serious ecological problems because they are not completely biodegradable and recyclable. The reduction of environmental pollution has led to a paradigm shift in the use of biodegradable materials, especially renewable raw materials in agriculture and waste processing industry food. This approach is equivalent to the conservation and recycling of natural resources, as well as the generation of new packaging of innovative design. The total packaging biodegradation generates benign products with the environment, and the permeability of CO2 and water is a parameter to be considered at the time of the development of the films. Natural polymers cross-linked and copolymerized with synthetic monomers are other alternatives to biodegradable packaging films. For the time being, the complete replacement of synthetic plastics is simply impossible to achieve and may even be unnecessary, at least for some specific applications that require our attention in the future. Definitely, biodegradable bio-packaging will be very promising in the near future [10–14]. For this reason, the development of edible films and coatings has been extensively studied in recent decades. These structures act as a barrier between food and the environment, helping the outer packaging in its protective function. In addition, some of them are supposed to have their own sensory or nutritional characteristics. The use of fruit purees in edible films has been previously explored by conferring distinctive flavors and colors that could be exploited for applications such as sushi wraps, fruit strips, or colorful coatings for specific foods [15].

using functionally active polymers. For example, if the packaging system has antimicrobial activity, packaging limits microbial growth by extending the latency period. Espitia et al. [27] performed an interesting review that describes the main methods for manufacturing edible pectin films, the main characterization techniques to determine their physico-mechanical properties, and the applications of

Extraction and Characterization of Pectins From Peels of Criolla Oranges…

Parris et al. [28] evaluated the water vapor permeability of hydrophilic films of alginate and pectin. Their results suggested that these diminished the mechanical properties by incorporating whole milk, sodium caseinate, skimmed milk powder, or whey in the film. In addition, this work evaluated the appropriate choice of plasticizer. Sodium alginate films exhibited lower water vapor permeability values than films prepared using low or high methoxylation pectin. The author found that sodium lactate was an effective plasticizer and alginate films containing 50% by weight or more of sodium lactate had an elongation greater than 13%. Films prepared with sorbitol as a plasticizer had the best water vapor permeability values but tended to be stiff and in some cases too fragile for tensile measurements. The addition of mixtures of whole milk to film effectively reduced water vapor permeability values by up to 35%. On the other hand, Pasini Cabello et al. [29] studied the effect of two plasticizers, glycerol (GLY) and polyethylene glycol (PEG), on the structure of the pectin films. The results revealed that glycerol acted as an internal plasticizer. Meanwhile, glycerin increased the predominant amorphous character of the plasticized films due to the decrease in intermolecular attraction, which resulted in degradation at low temperature and allowed the conformational transformation of the film to galacturonan ring through a can conformation. Glycerol produced more deformable and weaker films. In addition, glycerol produced films with a higher swelling index (SI) and a water vapor permeability value (WVP). When PEG was used as a plasticizer, a lower Young's modulus was obtained than the pure pectin film. However, by increasing the molecular weight of polyethylene glycol, more compact and less deformable films were obtained. WAXD spectra and DSC thermograms indicate that PEG works as a separate phase in the pectin matrix, more compact and less permeable to water vapor as the molecular weight of PEG increases. These results

Azeredo et al. [30] conducted the investigation of pomegranate juice into pectin films, giving it a bright red color, and also acted as a plasticizer. The increase in the pomegranate juice/water ratio from 0/100 to 100/0 resulted in an improved elongation (from 2 to 20%), a decrease in strength (from 10 to 2 MPa) and a Young's modulus (from 93 to <10 MPa), an increase in water vapor permeability (WVP,

35–24%). Although an effect of cross-linking (cross-linking) by citric acid was not confirmed, it is demonstrated by its effects on the films. Citric acid markedly increased MI (from <10% to almost 40%); in addition, when measured on a dry film basis, the effects of citric acid showed a notable tendency to increase resistance and modulus and to decrease WVP. The citric acid decreased the density of the red

Different characterization techniques allow to determine the properties of biopolymers. Some techniques are used in solution and others in film. The data in solution demonstrate the tendency of the biopolymer to interact with the solvent and the conformation it acquires, besides the possible implications of its molecular weight with the ability to form gels. The techniques that provide this important information are gel permeation chromatography [31–34], ultracentrifugationsedimentation, polarization to light, refractive index, light scattering, osmometry, diffusometry [24], viscosimetry, densimetry [26], and rheology [25, 35]. When the film is already formed, the most common analyses are water adsorption, either as

), and a decrease in insoluble matter (IM, of

edible pectin films as antimicrobial food packaging.

DOI: http://dx.doi.org/10.5772/intechopen.88944

show that PEG acts as an external plasticizer.

color, which suggests a destabilization of the anthocyanins.

from 3 to 9 g mm kPa<sup>1</sup> h<sup>1</sup> m<sup>2</sup>

9

The applications of biopolymers are from foods (nutritive and dietary fibers), packaging (biodegradable bags and/or protective films), thickening agents, gelling agents, foaming agents, and emulsifiers [16]. As films or membranes, are used in separative processes, for gas separation, diffusion, filtration and reverse osmosis [16]. In the pharmaceutical industry, the biofilms are used as drug encapsulants, films, and patches [17]. On the other hand, in mining industry, they are utilized as flocculating agents and precipitants of heavy metals [18].

The publications of biofilms are framed in the first place in the development of new materials from polysaccharides of great abundance and wood and agroindustrial production such as cellulose acetate [19] and starch [20]. Other polysaccharides available, but at high cost, are alginates [21], chitosan [22], and guar gum [23]. From an original point of view, the development of new films with biopolymers of various types such as arabinoxylans [24], soybean polysaccharides [25], and watercress polysaccharides [26] is worth highlighting. To clarify the latter, the latest advances in these films are described below.

#### 1.5.1 Regarding pectin films

Pectin due to its biodegradability, biocompatibility, edibility, and versatile chemical and physical properties (such as gelling, selective gas permeability, etc.) is a polymer matrix suitable for the production of edible films intended for the packaging of active foods. It is understood by an edible film as a packaging material, which is a thin layer of edible material placed on or between food components. Active packaging is a system that has basic barrier functions and others that are achieved by incorporating active ingredients in the packaging material and/or by

#### Extraction and Characterization of Pectins From Peels of Criolla Oranges… DOI: http://dx.doi.org/10.5772/intechopen.88944

using functionally active polymers. For example, if the packaging system has antimicrobial activity, packaging limits microbial growth by extending the latency period. Espitia et al. [27] performed an interesting review that describes the main methods for manufacturing edible pectin films, the main characterization techniques to determine their physico-mechanical properties, and the applications of edible pectin films as antimicrobial food packaging.

Parris et al. [28] evaluated the water vapor permeability of hydrophilic films of alginate and pectin. Their results suggested that these diminished the mechanical properties by incorporating whole milk, sodium caseinate, skimmed milk powder, or whey in the film. In addition, this work evaluated the appropriate choice of plasticizer. Sodium alginate films exhibited lower water vapor permeability values than films prepared using low or high methoxylation pectin. The author found that sodium lactate was an effective plasticizer and alginate films containing 50% by weight or more of sodium lactate had an elongation greater than 13%. Films prepared with sorbitol as a plasticizer had the best water vapor permeability values but tended to be stiff and in some cases too fragile for tensile measurements. The addition of mixtures of whole milk to film effectively reduced water vapor permeability values by up to 35%.

On the other hand, Pasini Cabello et al. [29] studied the effect of two plasticizers, glycerol (GLY) and polyethylene glycol (PEG), on the structure of the pectin films. The results revealed that glycerol acted as an internal plasticizer. Meanwhile, glycerin increased the predominant amorphous character of the plasticized films due to the decrease in intermolecular attraction, which resulted in degradation at low temperature and allowed the conformational transformation of the film to galacturonan ring through a can conformation. Glycerol produced more deformable and weaker films. In addition, glycerol produced films with a higher swelling index (SI) and a water vapor permeability value (WVP). When PEG was used as a plasticizer, a lower Young's modulus was obtained than the pure pectin film. However, by increasing the molecular weight of polyethylene glycol, more compact and less deformable films were obtained. WAXD spectra and DSC thermograms indicate that PEG works as a separate phase in the pectin matrix, more compact and less permeable to water vapor as the molecular weight of PEG increases. These results show that PEG acts as an external plasticizer.

Azeredo et al. [30] conducted the investigation of pomegranate juice into pectin films, giving it a bright red color, and also acted as a plasticizer. The increase in the pomegranate juice/water ratio from 0/100 to 100/0 resulted in an improved elongation (from 2 to 20%), a decrease in strength (from 10 to 2 MPa) and a Young's modulus (from 93 to <10 MPa), an increase in water vapor permeability (WVP, from 3 to 9 g mm kPa<sup>1</sup> h<sup>1</sup> m<sup>2</sup> ), and a decrease in insoluble matter (IM, of 35–24%). Although an effect of cross-linking (cross-linking) by citric acid was not confirmed, it is demonstrated by its effects on the films. Citric acid markedly increased MI (from <10% to almost 40%); in addition, when measured on a dry film basis, the effects of citric acid showed a notable tendency to increase resistance and modulus and to decrease WVP. The citric acid decreased the density of the red color, which suggests a destabilization of the anthocyanins.

Different characterization techniques allow to determine the properties of biopolymers. Some techniques are used in solution and others in film. The data in solution demonstrate the tendency of the biopolymer to interact with the solvent and the conformation it acquires, besides the possible implications of its molecular weight with the ability to form gels. The techniques that provide this important information are gel permeation chromatography [31–34], ultracentrifugationsedimentation, polarization to light, refractive index, light scattering, osmometry, diffusometry [24], viscosimetry, densimetry [26], and rheology [25, 35]. When the film is already formed, the most common analyses are water adsorption, either as

1.5 Films

A film is a uniform layer that can be formed either from a single component or from a mixture of polymers. The film development with biodegradable polymers is a promising technology in the food packaging industry. Food packaging is used for the preservation and protection of all types of food and its raw materials, particularly oxidative and microbial deterioration, as well as to extend the shelf life. The increased use of synthetic packaging films has led to serious ecological problems because they are not completely biodegradable and recyclable. The reduction of environmental pollution has led to a paradigm shift in the use of biodegradable materials, especially renewable raw materials in agriculture and waste processing industry food. This approach is equivalent to the conservation and recycling of natural resources, as well as the generation of new packaging of innovative design. The total packaging biodegradation generates benign products with the environment, and the permeability of CO2 and water is a parameter to be considered at the

Pectins - Extraction, Purification, Characterization and Applications

time of the development of the films. Natural polymers cross-linked and

or colorful coatings for specific foods [15].

flocculating agents and precipitants of heavy metals [18].

the latest advances in these films are described below.

1.5.1 Regarding pectin films

8

new materials from polysaccharides of great abundance and wood and

agroindustrial production such as cellulose acetate [19] and starch [20]. Other polysaccharides available, but at high cost, are alginates [21], chitosan [22], and guar gum [23]. From an original point of view, the development of new films with biopolymers of various types such as arabinoxylans [24], soybean polysaccharides [25], and watercress polysaccharides [26] is worth highlighting. To clarify the latter,

Pectin due to its biodegradability, biocompatibility, edibility, and versatile chemical and physical properties (such as gelling, selective gas permeability, etc.) is a polymer matrix suitable for the production of edible films intended for the packaging of active foods. It is understood by an edible film as a packaging material, which is a thin layer of edible material placed on or between food components. Active packaging is a system that has basic barrier functions and others that are achieved by incorporating active ingredients in the packaging material and/or by

copolymerized with synthetic monomers are other alternatives to biodegradable packaging films. For the time being, the complete replacement of synthetic plastics is simply impossible to achieve and may even be unnecessary, at least for some specific applications that require our attention in the future. Definitely, biodegradable bio-packaging will be very promising in the near future [10–14]. For this reason, the development of edible films and coatings has been extensively studied in recent decades. These structures act as a barrier between food and the environment, helping the outer packaging in its protective function. In addition, some of them are supposed to have their own sensory or nutritional characteristics. The use of fruit purees in edible films has been previously explored by conferring distinctive flavors and colors that could be exploited for applications such as sushi wraps, fruit strips,

The applications of biopolymers are from foods (nutritive and dietary fibers), packaging (biodegradable bags and/or protective films), thickening agents, gelling agents, foaming agents, and emulsifiers [16]. As films or membranes, are used in separative processes, for gas separation, diffusion, filtration and reverse osmosis [16]. In the pharmaceutical industry, the biofilms are used as drug encapsulants, films, and patches [17]. On the other hand, in mining industry, they are utilized as

The publications of biofilms are framed in the first place in the development of

steam or pure water, water vapor permeation, and swelling index, data that provide information about the affinity of water with the biopolymer. The mechanical tests (Young's modulus) help to elucidate the ductility of the material under study. The structural characteristics are determined by FTIR-ATR, diffraction of RX, SEM, and AFM [36], techniques that help to interpret parameters of the intimate nature of the film and the displacements in its signals caused by its chemical structure. The TGA-DTG and DSC data show the stability of the material against thermal changes during synthesis. In short, all these techniques give us information on the possible applications of each biopolymer and select what type of hydrolysis should be performed. Once the biopolymer has been obtained and characterized, permeoselectivity tests are carried out, such as the controlled release of drugs [37], coagulation or heavy metal precipitation [38], adsorption studies [39], gas permeation [40], and food packaging [41, 42].

In present work, pectin extraction from orange peel was carried out through the hydrolysis process; several extraction conditions were evaluated, specifically the pH in aqueous solution performing acid and basic hydrolyses at different concentrations and times but at constant temperature. Then the pectin obtained was characterized by a comparative analysis with commercial pectin with different techniques described below.

#### 2. Pectin extraction fundament

The citriculture in the international field is important not only for its nutrient and vitamin characteristics; it has also become a valuable source of raw materials to obtain the pectin, since it is found in the internal and external parts of the citrus peel. In our country there are several varieties of orange, from which you can obtain other byproducts besides juice, such as essential oils, fertilizers, concentrates, and pectin.

The purpose of this work is to exploit the waste of criolla orange peels, which in some cases causes pollution problems in the ecosystem as it is an adequate source for the proliferation of insects and microorganisms that are harmful to human health, in particular the by-products of citrus fruits used in the preparation of juices and marmalade. On the other hand, the industry generates an expense for the elimination of citrus waste if it is not used. Also, the lack of national raw materials for the pharmaceutical and food industry allows us to search for the natural resources that could be exploited. All these cases motivate to investigate the benefits obtained from citrus waste, such as oranges, which is used as an input for the agroindustry in the production of juices mainly, whose process involves a considerable generation of waste such as husks, pulp, and seeds. This has two benefits; on the one hand, it seeks to increase its "added value" with the process of agro industrialization and, on the other, reduce the environmental impact they produce.

In present work, the pectin extraction was carried out from the orange peel of the variety Citrus sinensis and through acidic or basic hydrolysis, by means of pH changes and extraction times at a constant temperature, with which it is expected to obtain a higher yield (Figure 3).

There are many processes for the extraction of pectin. In general, the raw material undergoes pretreatment that involves cleaning to remove foreign particles, washing to remove sugar and acid, drying, crushing, and storage. The substrate material is heated at reflux for several hours, with stirring, with an acid of known concentration (sulfur, sulfuric, nitric or hydrochloric acid) [43].

2.1 Pectin extraction from Citrus sinensis

Scheme of pectin production in this work.

Figure 3.

11

Many raw materials and products of the chemical and food Industry require preparation and conditioning. The process begins with the formation of flour from the raw material used, in this case the orange peel. Later, it is treated to achieve the necessary conditions that are required in the subsequent steps to obtaining the final

Extraction and Characterization of Pectins From Peels of Criolla Oranges…

DOI: http://dx.doi.org/10.5772/intechopen.88944

The objective of this work was to compare the different reagents used during hydrolysis and compare performance as well as mechanical, physical, and chemical behaviors. Also, the characterization techniques of pectin were in order to determine its quality.

Extraction and Characterization of Pectins From Peels of Criolla Oranges… DOI: http://dx.doi.org/10.5772/intechopen.88944

Figure 3. Scheme of pectin production in this work.

#### 2.1 Pectin extraction from Citrus sinensis

Many raw materials and products of the chemical and food Industry require preparation and conditioning. The process begins with the formation of flour from the raw material used, in this case the orange peel. Later, it is treated to achieve the necessary conditions that are required in the subsequent steps to obtaining the final

steam or pure water, water vapor permeation, and swelling index, data that provide information about the affinity of water with the biopolymer. The mechanical tests (Young's modulus) help to elucidate the ductility of the material under study. The structural characteristics are determined by FTIR-ATR, diffraction of RX, SEM, and AFM [36], techniques that help to interpret parameters of the intimate nature of the film and the displacements in its signals caused by its chemical structure. The TGA-DTG and DSC data show the stability of the material against thermal changes during synthesis. In short, all these techniques give us information on the possible applications of each biopolymer and select what type of hydrolysis should be performed. Once the biopolymer has been obtained and characterized,

Pectins - Extraction, Purification, Characterization and Applications

permeoselectivity tests are carried out, such as the controlled release of drugs [37], coagulation or heavy metal precipitation [38], adsorption studies [39], gas perme-

In present work, pectin extraction from orange peel was carried out through the hydrolysis process; several extraction conditions were evaluated, specifically the pH in aqueous solution performing acid and basic hydrolyses at different concentrations and times but at constant temperature. Then the pectin obtained was characterized by a comparative analysis with commercial pectin with different techniques

The citriculture in the international field is important not only for its nutrient and vitamin characteristics; it has also become a valuable source of raw materials to obtain the pectin, since it is found in the internal and external parts of the citrus peel. In our country there are several varieties of orange, from which you can obtain other byproducts besides juice, such as essential oils, fertilizers, concentrates, and pectin.

The purpose of this work is to exploit the waste of criolla orange peels, which in some cases causes pollution problems in the ecosystem as it is an adequate source for the proliferation of insects and microorganisms that are harmful to human health, in particular the by-products of citrus fruits used in the preparation of juices and marmalade. On the other hand, the industry generates an expense for the elimination of citrus waste if it is not used. Also, the lack of national raw materials for the pharmaceutical and food industry allows us to search for the natural

resources that could be exploited. All these cases motivate to investigate the benefits obtained from citrus waste, such as oranges, which is used as an input for the agroindustry in the production of juices mainly, whose process involves a considerable generation of waste such as husks, pulp, and seeds. This has two benefits; on the one hand, it seeks to increase its "added value" with the process of agro industrialization

In present work, the pectin extraction was carried out from the orange peel of the variety Citrus sinensis and through acidic or basic hydrolysis, by means of pH changes and extraction times at a constant temperature, with which it is expected to

The objective of this work was to compare the different reagents used during hydrolysis and compare performance as well as mechanical, physical, and chemical behaviors. Also, the characterization techniques of pectin were in order to determine its quality.

There are many processes for the extraction of pectin. In general, the raw material undergoes pretreatment that involves cleaning to remove foreign particles, washing to remove sugar and acid, drying, crushing, and storage. The substrate material is heated at reflux for several hours, with stirring, with an acid of known

and, on the other, reduce the environmental impact they produce.

concentration (sulfur, sulfuric, nitric or hydrochloric acid) [43].

ation [40], and food packaging [41, 42].

2. Pectin extraction fundament

obtain a higher yield (Figure 3).

10

described below.

product, the unit operations necessary to carry out the pectin formation process (see Figures 3–5).

bacteria or fungi, in addition to being in their commercial maturity. Once selected, the oranges are washed for later use. They are peeled manually without removing

In general, the drying of solids consists in separating small amounts of water or other liquid from a solid material in order to reduce the residual liquid content to an acceptably low value. The liquid to be vaporized can increase on the surface of the solid, as in the drying of saline crystals; inside the solid, as in the case of solvent removal of a sheet of a polymer; or part on the outside and part inside. The feeding of some dryers is a liquid in which the solid is suspended in the form of particles or in solution. The product that dries can withstand high temperatures or requires gentle treatment at low or moderate temperatures. This leads to the existence of a

The degradation of the polysaccharides begins, in general, at the reducing end of the molecule and proceeds step by step through the anhydroglucose chain [46]. The degradation of the polysaccharides proceeds by a peeling process in which the reducing end group is released from a chain by removing the remainder of the chain as a glycoxyl anion. The elimination takes place when the chain is in the beta

The extraction of pectin can be by acid or aqueous base. The basic extraction process produces a pectin of low degree of esterification (low methoxyl pectin) as a result of the saponification of the ester groups, while the acid extraction process generally produces a pectin with a high degree of esterification (high methoxyl pectin), approximately equal to the naturally occurring degree of esterification (DE). The high pectin has an esterification degree of 50% or more. Low DE and high pectin generally have different uses in food products, since they gel by differ-

In the extraction process with acid and base, the plant material was treated with acid or base at temperatures between 70 and 90°C for a sufficient time to eliminate the desired quantities and the quality of the pectin from the cellulose plant material. The pectin was separated from the reaction mixture by filtration. The pectin is precipitated from the extract juice by specific means, either precipitation with alcohol (ethyl or isopropyl can be used) or salifying with aluminum chloride. The precipitated pectin was separated from the precipitating solution by filtration. The extract obtained consists of those molecules that are soluble under the conditions of pH, time, and temperature used during extraction. The extract was composed of a mixture of pectins of different molecular weights and degrees of esterification. Molecular weights can vary from 100,000 to 200,000, but average molecular

Hydrolyzed pectins were compared against commercial pectin from citrus peel

This mechanism is frequently used in the food industry for the separation of solid particles contained in liquids as well as for the separation of two immiscible liquid phases. The driving force is the difference in density between the two phases [45].

the albedo, since it is rich in pectic substances.

DOI: http://dx.doi.org/10.5772/intechopen.88944

large number of types of commercial dryers in the market [45].

Extraction and Characterization of Pectins From Peels of Criolla Oranges…

position of a carbonyl group of the final reducing unit [47].

ent mechanisms. Both are sold commercially [48].

weights are more typically 140,000 g/mol [48].

2.4 Maceration and sedimentation

13

by Sigma (galacturonic acid ≥74.0%, methoxy groups 6.7%).

2.2 Drying of orange peels

2.3 Pectin obtainment

2.3.1 Hydrolysis

Selection, washing, and peeling of Citrus sinensis: In a first step, the oranges were manually selected. The quantity and quality of useful pectin obtained depend on the species of the fruit, the quantity that the fruit contains naturally, the state of maturation, the management conditions, and the enzymatic activity after harvesting and of the extraction process. They also depend on the part of the fruit that is used. For example, in unripened fruits the greater the amount of pectic material is insoluble in water, the quantity and the solubility increase with maturity [44].

It was decided to investigate as raw material the "criolla," orange which is a very common and easy-to-obtain species, observing that they do not present any type of microorganism or cuts and/or blows that may affect its safety or the development of

Figure 4.

Representative diagram of F pectins, with their respective performance.

Figure 5. Representative diagram for thermal hydrolysis with its respective performance.

bacteria or fungi, in addition to being in their commercial maturity. Once selected, the oranges are washed for later use. They are peeled manually without removing the albedo, since it is rich in pectic substances.

## 2.2 Drying of orange peels

product, the unit operations necessary to carry out the pectin formation process

water, the quantity and the solubility increase with maturity [44].

Pectins - Extraction, Purification, Characterization and Applications

Selection, washing, and peeling of Citrus sinensis: In a first step, the oranges were manually selected. The quantity and quality of useful pectin obtained depend on the species of the fruit, the quantity that the fruit contains naturally, the state of maturation, the management conditions, and the enzymatic activity after harvesting and of the extraction process. They also depend on the part of the fruit that is used. For example, in unripened fruits the greater the amount of pectic material is insoluble in

It was decided to investigate as raw material the "criolla," orange which is a very common and easy-to-obtain species, observing that they do not present any type of microorganism or cuts and/or blows that may affect its safety or the development of

(see Figures 3–5).

Figure 5.

12

Figure 4.

Representative diagram for thermal hydrolysis with its respective performance.

Representative diagram of F pectins, with their respective performance.

In general, the drying of solids consists in separating small amounts of water or other liquid from a solid material in order to reduce the residual liquid content to an acceptably low value. The liquid to be vaporized can increase on the surface of the solid, as in the drying of saline crystals; inside the solid, as in the case of solvent removal of a sheet of a polymer; or part on the outside and part inside. The feeding of some dryers is a liquid in which the solid is suspended in the form of particles or in solution. The product that dries can withstand high temperatures or requires gentle treatment at low or moderate temperatures. This leads to the existence of a large number of types of commercial dryers in the market [45].
