**4. Gum characterization**

#### **4.1 Spectroscopic methods for gum characterization**

"Structure is the key to everything in chemistry. The properties of a substance depend on the atoms it contains and how these atoms are bound. Less obvious, but very powerful, is the idea that someone with knowledge of chemistry can look at the structural formula of a substance and say several things about its properties" [36]. "Looking at the structural formula" inevitably refers to the use of techniques that assist in the chemical and structural knowledge of organic molecules, and in this context, spectroscopic techniques can be a very important tool to fulfill such function [37].

In order to know the properties of polysaccharides or glycoconjugates, it is essential to elucidate and characterize the structural and dynamic aspects of their molecules [38]. Carbohydrate chemistry can rely on one of the most efficient spectroscopic techniques for investigating organic compounds in solution: Nuclear Magnetic Resonance (NMR), which has advanced methods, and becomes essential in the characterization of polysaccharides with complex structures [39, 40].

The commonly used NMR techniques are hydrogen (1 H), carbon-13 (13C), homonuclear correlations (1 H-1 H), COSY (homonuclear Correlation Spectroscopy), and 13C-1 H HMQC (Heteronuclear Multiple Quantum Coherence) [41].

The elements that are most common in organic molecules (carbon and hydrogen) have isotopes (1 H and 13C) capable of providing NMR spectra rich in structural information. A proton nuclear magnetic resonance spectrum (1H NMR) provides information about the environments of the various hydrogens present in a molecule. A carbon-13 nuclear magnetic resonance spectrum (13C NMR) does the same for carbon atoms [36, 38].

NMR spectrum of coconut trunk gum (*Cocos nucifera*), obtained by alkaline extraction, presented approximately 10 signs in the anomeric region, which reveals a complex structure. The signals made reference to the presence of L-Araf (δ 108.6–107.0); α-Arap (δ 103.1); β-Xylp (δ 101.6), and also α-Fucp and α-Glcp units (δ 100.5–99.2), bonded to C-4. Reducing terminals were bonded to C-5 [35].

Peach gum (*Prunus persica*) was also considered as a complex molecule, as it shows 8 signs in the anomeric region (δ 110–90). The main sign in δ 103.2 refers to β-D-Galp units in the main chain, and the sign in δ 102.8 suggests the presence of β-D-GlcAp. In the substituted carbon region, the signs in δ 84.1 and δ 82.0–82.5 refer to C-3 of the replaced units α-L-Araf and β-D-Galp 3-O-, respectively [42]. These are examples that demonstrate that the NMR technique is an indispensable tool for the knowledge of polysaccharides and their properties.

Another technique widely used for the structural identification of polysaccharides, even before the advent of NMR, is the Fourier-Transform Infrared Spectroscopy (FTIR) [36]. Although NMR gives more information about the structure of an unknown compound, infrared is important because it can identify certain functional groups. Structural units, including functional groups, vibrate in characteristic ways, and this sensitivity to group vibrations forms the basis of infrared spectroscopy [43].

Molecular movements are described by two types of vibrations: deformation and stretching (**Figure 5**). The deformation causes a bond angle change that can occur in or out of the molecular plane of symmetry; and the stretching is a linear

**239**

**Table 1.**

*functional groups.*

*Gums—Characteristics and Applications in the Food Industry*

intermittent movement so that the interatomic distance changes constantly. It can

When irradiated by infrared light, the atoms of the molecular structure of a given sample absorb it. The vibration or rotation will depend on the type of chemical bond formed by these atoms B [45, 46]. **Table 1** shows some bands of infrared

acid

1280 and 1220 cm−1 Methyl ester groups (CH3) in pectates [51] 1280–1260 cm−1 Phenolic esters bonded to cell walls groups [52] ≈1230 cm−1 Amide III of protein secondary structures [49, 52]

Fingerprint region in polysaccharides [53]

chains of Araf

1141–1039 cm−1 Arabinans connected to the main and side

1139–985 cm−1 Arabinogalactans linked to the main chain

1140–975 cm−1 Arabinogalactan-rhamnoglycan attached

**Possible assignments to bands References**

[48, 50]

[53]

[53]

[53]

Amide I and II of proteins, respectively [47–50]

Methyl ester groups (CH3) in pectins [51]

Galactan attached to main chain β 1➔6 Galp [53]

of β 1➔3 Galp, and side chain of α 1➔3 Araf

to the main chain β 1➔6 Galp (24%) and α 1➔4 Rhap (42%), and side chain of α-Araf

(8%) and β 1➔6 Galp (92%)

and α 1➔5 Arap (34%)

900–870 cm−1 Β-type bonds between monosaccharides [54, 55]

*Infrared Fourier transform bands in plane (*δ*); out of plane (*γ*) and stretching (v), and assignments related to* 

Carboxylic acids deprotonated in uronic

*DOI: http://dx.doi.org/10.5772/intechopen.95078*

be symmetrical or asymmetrical [44].

**Bands Associated** 

≈1650 and 1550 cm−1 v(C═O)

1155–1038 cm−1 v(C▬O▬C)

1640–1600 and 1420 cm−1

1444, 1371, 975–978, and 923 cm−1

*Aspects of the molecule vibrations observed in infrared spectroscopy.*

**vibrations**

γ(CN) δ(NH) (CCN)deform. v(C═C) v(COO− )

δ(CH3) (CH)deform. δ(CO) δ(NH) δ(C▬O) δ(OH)COOH v(C▬O▬C) v(CN)

v(C▬OH) v(C▬O) v(C▬C) v(O▬CH3) (CH3) (C1▬H) δ(OH) δ(CCH) δ(COH)

**Figure 5.**

*Gums—Characteristics and Applications in the Food Industry DOI: http://dx.doi.org/10.5772/intechopen.95078*

**Figure 5.**

*Innovation in the Food Sector Through the Valorization of Food and Agro-Food By-Products*

composed of Xylp joined by β-(1➔4) bonds.

**4.1 Spectroscopic methods for gum characterization**

The commonly used NMR techniques are hydrogen (1

H-1

**4. Gum characterization**

homonuclear correlations (1

gen) have isotopes (1

for carbon atoms [36, 38].

infrared spectroscopy [43].

and 13C-1

Non-reducing units substituted at 3-O (Araf - 8%); 3,4-di-O-(15%); 2,4-di-O (5%); and 2.3.4-tri-O (Xylp 17%) positions were also found, attached to a main chain

"Structure is the key to everything in chemistry. The properties of a substance depend on the atoms it contains and how these atoms are bound. Less obvious, but very powerful, is the idea that someone with knowledge of chemistry can look at the structural formula of a substance and say several things about its properties" [36]. "Looking at the structural formula" inevitably refers to the use of techniques that assist in the chemical and structural knowledge of organic molecules, and in this context, spectroscopic techniques can be a very important tool to fulfill such function [37]. In order to know the properties of polysaccharides or glycoconjugates, it is essential to elucidate and characterize the structural and dynamic aspects of their molecules [38]. Carbohydrate chemistry can rely on one of the most efficient spectroscopic techniques for investigating organic compounds in solution: Nuclear Magnetic Resonance (NMR), which has advanced methods, and becomes essential in the characterization of polysaccharides with complex structures [39, 40].

H HMQC (Heteronuclear Multiple Quantum Coherence) [41]. The elements that are most common in organic molecules (carbon and hydro-

information. A proton nuclear magnetic resonance spectrum (1H NMR) provides information about the environments of the various hydrogens present in a molecule. A carbon-13 nuclear magnetic resonance spectrum (13C NMR) does the same

NMR spectrum of coconut trunk gum (*Cocos nucifera*), obtained by alkaline extraction, presented approximately 10 signs in the anomeric region, which reveals

Another technique widely used for the structural identification of polysaccharides, even before the advent of NMR, is the Fourier-Transform Infrared Spectroscopy (FTIR) [36]. Although NMR gives more information about the structure of an unknown compound, infrared is important because it can identify certain functional groups. Structural units, including functional groups, vibrate in characteristic ways, and this sensitivity to group vibrations forms the basis of

Molecular movements are described by two types of vibrations: deformation and stretching (**Figure 5**). The deformation causes a bond angle change that can occur in or out of the molecular plane of symmetry; and the stretching is a linear

a complex structure. The signals made reference to the presence of L-Araf (δ 108.6–107.0); α-Arap (δ 103.1); β-Xylp (δ 101.6), and also α-Fucp and α-Glcp units (δ 100.5–99.2), bonded to C-4. Reducing terminals were bonded to C-5 [35]. Peach gum (*Prunus persica*) was also considered as a complex molecule, as it shows 8 signs in the anomeric region (δ 110–90). The main sign in δ 103.2 refers to β-D-Galp units in the main chain, and the sign in δ 102.8 suggests the presence of β-D-GlcAp. In the substituted carbon region, the signs in δ 84.1 and δ 82.0–82.5 refer to C-3 of the replaced units α-L-Araf and β-D-Galp 3-O-, respectively [42]. These are examples that demonstrate that the NMR technique is an indispensable

tool for the knowledge of polysaccharides and their properties.

H), carbon-13 (13C),

H), COSY (homonuclear Correlation Spectroscopy),

H and 13C) capable of providing NMR spectra rich in structural

**238**

*Aspects of the molecule vibrations observed in infrared spectroscopy.*

intermittent movement so that the interatomic distance changes constantly. It can be symmetrical or asymmetrical [44].

When irradiated by infrared light, the atoms of the molecular structure of a given sample absorb it. The vibration or rotation will depend on the type of chemical bond formed by these atoms B [45, 46]. **Table 1** shows some bands of infrared


#### **Table 1.**

*Infrared Fourier transform bands in plane (*δ*); out of plane (*γ*) and stretching (v), and assignments related to functional groups.*

spectroscopy and their respective functional groups present in polysaccharides. It is also possible to see that FTIR can provide information on important functional groups in polysaccharides in the fingerprint region [44, 46].

In polysaccharides, the infrared spectroscopy can be used to qualitatively observe possible structural changes. Quelemes et al., [56] demonstrated the structural change in cashew gum when submitted to quaternary ammonium reagent, which also improved some properties such as biocompatibility and antimicrobial action. FTIR was also efficient to demonstrate that the interaction of gum arabic and chitosan was formed by electrostatic complexes, a result of the interaction between functional groups (NH3<sup>+</sup> and ▬COO-) of both macromolecules. Also, it improved viscoelastic characteristics at different pH's, demonstrating its complex versatility for use as food additives [57].

#### **4.2 Thermal analysis of gums**

Most polymers, synthetic or natural, suffer degradation when subjected to thermal stress [58]. This is attributed to chain depolymerization, point splits, or even the elimination of low molecular weight fragments, which cause mass loss due to the increase in temperature [59]. They cause thermal effects related to physical or chemical changes, and are associated with thermodynamic events [58]. These changes in energy and mass can be measured by thermogravimetry (TG), derivative thermogravimetry (DTG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC), which make it possible to obtain information such as changes in the crystalline structure, reaction kinetics, melting and boiling point, glass transition, and others [60]. Changes in mass as a function of temperature and/or time [61] and continuous registration of mass subjected to heating or cooling [62] are definitions attributed to thermogravimetry.

Being the combination of an electronic microbalance and an oven, associated with a linear temperature programmer, thermogravimetric analysis consists of submitting a known mass of sample inside a crucible, suspended by a platinum wire, to a programmed temperature gradient, for a predefined time, which is automatically registered, simultaneously with the sample mass [63].

In DTG, the mass variation derivative (dm/dt) is registered as a function of temperature or time. In this method, the levels observed in TG are replaced by peaks that delimit areas which are proportional to the changes in mass suffered by the sample and can indicate the exact initial temperatures and maximum speed of reactions. DTG allows a clear distinction of successive reactions (not detected by TG), by quantitative determinations of loss or gain of mass which are associated with the peak areas [60].

DSC and DTA are analyses that measure energy gradients between the sample and a reference material subjected to controlled temperature. DSC is a calorimetric method in which energy differences are measured, whereas in DTA, temperature differences between the sample and the reference material are registered [59]. DTA provides a qualitative analysis of the thermal events experienced by the sample, whereas DSC is able to quantify such events because it measures the heat flow through a temperature gradient [64].

Changes in composition, food processing temperatures or ingredients result in changes in phase transitions of the product [65]. Quantifying the variables involved in these phenomena, such as temperature or thermodynamic quantities, is important for understanding processes such as evaporation, dehydration, and freezing [66]. Being the responsible for plasticizing effects and important component of food, water and its state transitions (gaseous or crystalline) guide such processes, and can also be used to describe the effects of temperature on physical properties [59].

**241**

starch products.

*Gums—Characteristics and Applications in the Food Industry*

identified, consequently showing a more elastic structure [69].

sible for rheological changes was observed [69, 71].

*Acacia tortuosa* gum, originating from species located in South America (Venezuela) (15% m/v), presented elastic modulus (G') greater than its viscous modulus (G"), indicating the occurrence of a gel material that became progressively weaker with increasing temperature [71]. In both studies, gums showed transition from Newtonian to non-Newtonian behavior with increasing concentration. Also, the influence of inter and intramolecular structural interactions as agents respon-

The emulsifying and rheological characters of chemically modified gum arabic (*Acacia senegal*) (esterified with octenyl succinic anhydride (OSA) at different concentrations) was measured by [72]. The study revealed that the gum presented an increase in its emulsifying capacity and a gradual increase in apparent viscosity with increasing OSA content, indicating satisfying emulsion stability and potential use as microencapsulant. The electrostatic interaction between gum arabic and soy protein β-conglycinin was the mechanism that improved the flocculating action of *Acacia senegal*, in addition to providing greater elasticity at the oil/water interface of the gum, consequently improving its emulsifying capacity [73]. The interaction of gum arabic with native tapioca starch also provided improved product elasticity and adhesiveness [74]. Chenlo, Moreira, & Silva, [75], studied the rheology of aqueous dispersions of tragacanth gum and guar gum (10 g/L) during storage for 47 days. In general, the apparent viscosity decreased significantly (α = 0.05) for both systems at low values of γ ̇ (< 10s−1) and remained constant above this value. The decrease in viscosity was lower for tragacanth gum and lasted until the

15th day, whereas for guar gum, the decrease occurred until the 20th day.

and 1% m/v) were rheologically evaluated by Hussain, Singh, Vatankhah, & Ramaswamy, [76], who found that the addition of locust bean gum at low concentrations (0.125%) made the mixture behave as a liquid at low oscillatory frequencies (0.1 to 10 rad/s). It also presented increased elasticity, with typically solid behavior at concentrations of 0.5 to 1%, at higher frequencies (15 to 100 rad/s). Thus, locust bean gum has potential to specifically modify the structure and texture of corn

Mixtures of corn starch (5% m/m) and locust bean gum (0; 0.125; 0.25; 0.50;

The research results showed that there are many variables that influence the rheological characteristics of gums. Among them, the fine chemical structure of the polysaccharide, their interactions, and molecular conformations can be highlighted,

which confirms the importance of characterizing the structure of new gums.

Natural polymers are of particular interest in rheological studies [67]. Their thickening, emulsifying, gelling, and stabilizing properties, which enable them to be used in food, pharmaceutical, and cosmetic industries are supported by a series of inter and intramolecular association mechanisms inherent to each polymer. Such mechanisms lead them to particular applications in different processes and products [68]. Gum arabic *(Acacia senegal)* 3% (m/v), originating from African regions such as Sudan, Senegal, and Mali, has typical behavior of a liquid. Sanchez, Renard, Robert, Schmitt, & Lefebvre, [69] investigated G' and G" in gum arabic, where G' is the storage modulus and indicates the portion of energy (from the applied voltage) that is temporarily stored during the test, and it provides information on the elastic characteristic of the fluid. On the other hand, G" is the loss modulus, which indicates the portion of energy used to initiate flow. It is irreversibly transferred in the form of heat and provides information on the viscous characteristics of the fluid [70]. The authors state that gum arabic presented a viscous modulus (G') greater than its elastic modulus (G'), but after 5 hours of rest, gel characteristics were

*DOI: http://dx.doi.org/10.5772/intechopen.95078*

**4.3 Gum rheology**
