Advanced Biophysical Techniques for Polysaccharides Characterization

Advanced Biophysical Techniques for Polysaccharides Characterization offers a detailed insight into the cutting-edge techniques available for the identification, quantification, characterization and structural analysis of polysaccharides. A wide range of techniques are covered, including scanning electron microscopy (SEM), atomic force microscopy (AFM), optical microscopy, non-linear optical microscopy and spectroscopic techniques like Fourier transform Infrared (FTIR), X ray diffraction, light scattering, and nuclear magnetic resonance (NMR). Dynamic Nuclear Polarization and TEM techniques are also considered. Various polysaccharides are investigated along with their applications across a range of industries. Each chapter offers a detailed description of the techniques before delving into case studies covering the latest advances.

This book provides a one-stop solution to the latest advanced microscopic and spectroscopic techniques for investigating a range of important polysaccharides and is an ideal reference for researchers in the field of biophysics, molecular biology, biochemistry, pharmaceutics, food chemistry and related areas.

• Covers a range of biophysical techniques for polysaccharide analysis, including NMR, Dynamic Nuclear Polarization, mass spectrometry approaches, X ray diffraction, light scattering, and TEM techniques
• Investigates an array of polysaccharides such as glycogen, xanthan, hyaluronan, and more
• Includes an introduction to the sources, types, and benefits of polysaccharide
• Considers applications of polysaccharides in various industries, including biomedicine, pharmaceuticals, and the food industry

• Language: English
• Publisher: Academic Press
• Release date: Jun 14, 2024
• ISBN: 9780443140433

Book preview

Chapter 1: Physicochemical modification and characterization of starch used in the food industry: A review

Shruthi Shetty¹, Indira Govindaraju¹, Adline Siona Rebello¹, Divyani Chatterjee¹, Md. Hafizur Rahman², and Nirmal Mazumder¹     ¹Department of Biophysics, Manipal School of Life Sciences, Manipal Academy of Higher Education, Manipal, Karnataka, India     ²Department of Quality Control and Safety Management, Faculty of Food Sciences and Safety, Khulna Agricultural University, Khulna, Bangladesh

Abstract

Starch is a biodegradable polysaccharide that occurs naturally. It is the principal source of energy in the human diet as well as a chief food component. Starches have a wide application in the food along with nonfood industries. However, native starch has restricted function owing to its shortcomings like the high tendency for retrogradation and decomposition, low thermal stability and shear resistance, inertness, and resilience to enzymolysis that are required for the particular type of treatment. To overcome these shortcomings and to meet the current challenging industrial requirements, starch is modified by means of physical (annealing, pregelatinization, heat moisture treatment, osmotic pressure treatment, ultrasonication, pulsed electric field), chemical (cross-linking, esterification, acetylation, acid hydrolysis), enzymatic (α-amylase, β-amylase, isoamylase, pullulanase), or a combination of these. All the techniques bring about physicochemical alterations of the natural starch to advance its utilization in definite food application by tailoring its functional properties.

Keywords

Amylase; Annealing; Cross-linking; Food industry; Heat moisture treatment; Starch

1. Introduction

Starch is a polysaccharide which occurs naturally. It is an economic, and biodegradable, accessible polysaccharide (Neelam et al., 2012). It is a principal energy source in the human diet as well as a chief food component (Shi et al., 2019). Chemically, the starch molecule is comprised of two polysaccharide units, namely amylose and amylopectin, both of which include hundreds to thousands of glucose units. Amylose is a linear and amorphous molecule, joined by α-1,4 glycosidic bonds. Amylopectin is a crystalline and highly branched molecule linked by α-1,4 glycosidic bonds in a linear arrangement and α-1,6 glycosidic bonds at the branching site (Bashir & Aggarwal, 2019; Chakraborty et al., 2020). Amylose consists of approximately 500–2000 glucose units that account for 20%–30% of total starch, whereas amylopectin consists of over 1,000,000 glucose units (Bashir & Aggarwal, 2019; Egharevba, 2020).

Starch is extensively used as a bulking agent, gelling agent, thickener, and water-retaining agent in food industries. It significantly contributes to the textural properties of several foods and has the ability to modify viscosity, texture, adhesion, moisture retention capacity, and formation of gel and films (Alcázar-Alay et al., 2015; Singh et al., 2007). Starch is currently exploited as a food preservative to regulate the sauce and soup texture, to improve the shelf life of products and to increase the resistance to gel breakdown during the various processing technique (Santana & Meireles, 2014). The main application of starch is in bakery products, meat products, snacks, gravies and sauces, batters, and dairy confectionery where it is accountable for the structure and attributes of end products (Alcázar-Alay et al., 2015; Zia-ud-Din et al., 2017). Owing to the higher consumption rate, bread and cakes are the most significant bakery products. Starch is used as a molding powder to produce different kinds of sweets in the confectionery industry as it is frequently utilized in its granular form. It also finds application in the preparation of fast and fried foods like noodles and various sorts of pasta (Alcázar-Alay et al., 2015). During the manufacture of potato chips, the crisp texture depends mainly on the starch constituent of potato tubers, where the peeled tubers produce crisp in most cases followed by the influence of nonstarch polysaccharide, lignin, and protein nitrogen (Kita, 2002). Native starch (NS) that has undergone modification via oxidation and acetylation may be utilized as food additives (Yazid et al., 2018). Usually, modified starches find application as a binder in breaded and battered foods, fat replacer, in fried snacks as crisping cover, gelling agents in jelly gum, seasoning for snack and meat, to enhance juiciness in salad dressings and ice cream, to capture the flavor in beverage gasses, emulsion stabilizers in drinks, and foam stabilizer in marshmallows (Egharevba, 2020). Starch finds application in various industries and this review focuses on the various techniques used for the modification of starch and how these alterations are useful, especially in food industries.

Starch lacks certain physical and chemical properties in its natural form owing to its shortcomings like the high tendency for retrogradation and decomposition, inert, low thermal stability and shear resistance, insoluble in water at room temperature, and exceedingly resilient to enzymatic degradation that is required for a particular type of treatment (Alcázar-Alay et al., 2015; Berski et al., 2011; Zia-ud-Din et al., 2017). As a result of their instability to fluctuations in parameters like pH and temperature, has led to the inadequacy of application of NS directly (Berski et al., 2011). Certain properties, including insolubility in cold water, reduced starch paste clarity, low syneresis, and reduction in thickening power and viscosity postcooking, restrict the application of starch in the food industry (Korma et al., 2016; Yazid et al., 2018). Therefore, to improve the properties of starchy food materials like texture, solubility, viscosity, adhesion, and thermal stability, NS is modified to find diverse application in various industries (Egharevba, 2020; Singh et al., 2007; Sweedman et al., 2013).

To meet the current challenging industrial requirements, a few properties of starch are altered by various modification methods that have improved its flexibility along with satisfying the demands of consumer (Egharevba, 2020). Starch modification is a process of altering the chemical and physical attributes of the NS to enhance its utilization by diversifying its functional properties (Cai et al., 2014). This process also produces products with diverse novel functional properties. With the purpose of improving and encouraging deserved functional characteristics, starches are often altered by physical, chemical, enzymatic, and genetic approaches (Zia-ud-Din et al., 2017). Physical and chemical modifications are quite common, whereas enzymatic and genetic modification, being a biotechnological method, are progressively being discovered (Egharevba, 2020). Table 1.1 explains the application of various starch modification techniques in the food industry. Modified starch is prepared by partly altering the starch physiochemical properties by the various treatments which can then be used as a food additive (Abbas et al., 2010). Most starch modification, especially those involved in the food industry, recommends the introduction of lower amounts of a substituent group, with less degree of substitution (DS) (0.2–0.0001 or, less) (Singh et al., 2010). In Trela et al., the observation was that synthesized acetylated cassava starch with medium and low DS showed increased solubility and swelling properties, whereas higher DS showed a reduction in these parameters (Trela et al., 2020). Acetylated corn starches with varying DS (DS 0.85, DS 1.78, DS 2.89) were synthesized in the occurrence of acetic acid using acetic anhydride at different temperatures. As DS increased, an enhancement was observed in the intensities of typical absorption of esterified starch (Chi et al., 2008). This review article deals with common starch modifications in the food industry and the techniques used for their characterization.

Table 1.1

2. Common physicochemical modifications of starch in the food industry

2.1. Physical modifications

The physical modification includes the alterations in the 3-D structure and morphology of NS under the influence of various physical parameters like moisture, temperature, pressure, radiation, pH, ultrasonic waves, etc (Nawaz et al., 2020). It is the most preferred method as it is easy, cost-effective, and does not include chemicals or biological agents (harmless) and hence is used for human utilization (Alcázar-Alay et al., 2015; Ashogbon & Akintayo, 2014). Heating the starch in aqueous alcohol, high temperature and pressure produces granular cold-water-soluble starches that display smoother texture, increased processing tolerance, and higher viscosity (Zia-ud-Din et al., 2017). The traditional methods for physical modification include annealing (ANN), pregelatinization, and heat-moisture treatment (HMT), whereas the recent techniques include osmotic pressure treatment (OPT) (Gayary & Mahanta, 2020), superheated starch (Hu et al., 2018), pulsed electric fields (PEFs) treatment (Chen et al., 2021), numerous deep freezing and thawing (Yu et al., 2015), thermally inhibited treatment (dry heating), micronization in a vacuum ball mill, mechanical activation with a stirring ball mill (He et al., 2014), and dual modifications (Zhao, Yu, et al., 2018). A few techniques like dry heating, superheating, PEFs, OPT, and stirring ball milling appear inexpensive and simple, resulting in a noticeable transformation in their physicochemical properties (Egharevba, 2020). Pregelatinized (precooked) starch is used as a thickening agent in cold water, whereas the heat-treatment process includes ANN and HMT that results in starch physical modification without granular damage, gelatinization, or birefringence loss (Miyazaki et al., 2006). Pinhão (Araucaria angustifolia) starch was physically modified using a combination of treatments such as HMT, ANN, and sonication (Pinto et al., 2015). A few physical modification techniques are discussed below.

2.2. Hydrothermal modification

ANN and HMT are two hydrothermal treatments that maintain granule integrity without damaging the structure (Jacobs & Delcour, 1998; Zia-ud-Din et al., 2017). Principally, when there is a shift of starch polymers from the amorphous state to the semicrystalline region, the hydrothermal modification takes place (Alcázar-Alay et al., 2015). Gelatinization is the process of heating starch granules causing them to swell and release amylose by diffusion (from enlarged starch granules) in presence of adequate water. This results in the formation of an amylose–amylopectin gel when the mixture cools down. This helps in generating a viscous solution due to the aggregation of swollen amylopectin-enriched granules to form gel particle. The resulting two-phase structure is known as starch paste that finds application in the food industry where the processed starch is used as thickeners or binders. Initially, the amorphous area is the site for gelatinization due to the presence of fragile bonds; it then spreads to the crystalline region. The gelatinization process is symbolized by transition temperatures and high transition temperature represents high crystallinity degree and stability and high resistance of starch to gelatinization (Alcázar-Alay et al., 2015; Egharevba, 2020). Based on the gelatinization temperature of starch, hydrothermal treatments can be classified as pregelatinization, ANN, and HMT.

2.2.1. Pregelatinization

Pregelatinization is the simplest starch modification technique that includes cooking of starch slurry until it is completely gelatinized followed by a simultaneous (or preceding) drying procedure including drum or spray drying and extrusion. Pregelatinized starches (instant starches) form a steady suspension that dissolves in cold water. It preserves the integrity of starch while enabling cold water thickening. Therefore, pregelatinized starches are applied widely in the food industry as a gelling factor, adhesive in foundry core binders, and the textile industry. The main outcome of this technique is the destruction of granules resulting in granular fragmentation, increase in solubility, swelling ability, cold water dispersion, and viscosity (Alcázar-Alay et al., 2015; Singh et al., 2010; Zia-ud-Din et al., 2017). Majzoobi et al. conducted a study using a twin drum drier to produce pregelatinized wheat starch, examining its physicochemical properties. SEM images indicated that native wheat starch contained both large and small granules. Conversely, pregelatinized wheat starch displayed randomly distributed air bubbles in a sheet-like formation, suggesting complete gelatinization during drying and the destruction of the granular structure. X-ray diffraction (XRD) results showed that native wheat starch had a typical A-type crystalline pattern due to its semicrystalline structure. However, pregelatinized starch showed no well-defined crystalline structure, and the process disrupted the A-type pattern in NS. The degree of crystallinity in pregelatinized starch was notably lower at 2.22%, in stark contrast to the 40.08% degree of crystallinity observed in NS (Majzoobi et al., 2011). In a separate study by Okunlola et al., bitter yam and Chinese yam starches underwent pregelatinization and acetylation, with native corn starch (commercial) and pregelatinized potato starches serving as standards. The differntial scanning calorimetry (DSC) curves revealed that the endothermic peaks for pregelatinized bitter and Chinese yam starches shifted slightly to higher temperatures (from 111.56 to 123.52°C for bitter yam and 101.14 to 108.88°C for Chinese yam). This shift was accompanied by a reduction in enthalpy for both bitter and Chinese yam starches. The NS, being partially crystalline, has a lower amorphous region magnitude compared to pregelatinized starch, potentially explaining the observed variations in gelatinization temperatures and enthalpies. The DSC curves for acetylated bitter and Chinese yam starches shifted to lower temperatures, indicating a decrease in intermolecular hydrogen bonds, where the acetyl group replaced the hydroxyl group (Okunlola et al., 2015).

2.2.2. Annealing

ANN is a type of hydrothermal modification technique that takes place in the presence of water and heat, i.e., in excess (76% w/w) or medium water (40%–50% w/w) with a sustained temperature above the glass transition temperature (Tq) but below the onset (To) of gelatinization temperature (Kushwaha & Kaur, 2018, pp. 1–15). ANN offers theoretic validation for the development of a substance by progressing its mechanical characteristics and thermal stability (Vermeylen et al., 2006). It results in the alteration of physicochemical properties of the starch granules without damaging its structure (Kushwaha & Kaur, 2018, pp. 1–15). The physical goal of ANN is to move toward the glass transition temperature without activating gelatinization, which enhances molecular mobility (Alcázar-Alay et al., 2015; Neelam et al., 2012). In a recent investigation conducted by Wang et al., the impact of ANN treatment at different temperatures on wheat, yam, and potato starches was studied. In wheat starch, there was an overall increase in paste viscosity at 30 and 40°C, while at 50°C, a notable reduction in paste viscosity was observed. This was credited to the heightened order of starch chains in the amorphous region. Examination through scanning electron microscopy (SEM) images indicated that native wheat starch granules included both large and small-sized granules, featuring grooves on the surface. Wheat starch subjected to ANN at 30 and 40°C (represented as Fig. 1.1a-W-30, W-40) did not exhibit significant differences compared to the NS. However, ANN at 50°C (Fig. 1.1a-W50) resulted in the destruction and fusion of starch granules. SEM studies revealed that native yam starch displayed elliptical and oval-shaped granules with smooth surface, whereas potato starch displayed oval and spherical shape. It was also studied that ANN did not bring about any noteworthy alteration in morphology of yam starch (Fig. 1.1a-YN, Y-30, Y-40, Y-50) and potato starch (Fig. 1.1a-PN, P-30, P-40, P-50). No significant difference in the granule morphology of ethanol dehydrated potato starch was observed (Fig. 1.1a-EP-N, EP-30, EP-40, EP-50). The XRD results of native wheat starch exhibited an A-type crystalline form with specific peaks at 15.1 (singlet), 17.1 (doublet), 18.0 (doublet), and 23.2 degrees (singlet) (2Ɵ), and while ANN at 30 and 40°C showed no significant alterations in crystallinity, ANN at 50°C led to a reduction in starch crystallinity from 22.6% to 14.3%, indicating the starch crystallites destruction (Fig. 1.1b-1.i). Native yam starch presented two peaks (both singlets) at 15.4 and 23.0 degrees, and an unresolved peak (doublet) at 17.1 and 17.9 degrees (2Ɵ), indicating a combination of A- and B-type polymorphs (C-type) (Fig.1.1b-1.ii). Seven characteristic B-type diffraction peaks at 5.7, 15.1, 17.2, 19.6, 22.2, 24.0, and 26.2 degrees (2Ɵ) (Fig.1.1b-1.iv) were seen in the ethanol-dehydrated potato starch; only two diffraction peaks at 17.0 and 23.0 degrees (2Ɵ) (Fig.1.1b-1.iii) were seen in freeze-dried potato starch. Potato and yam starches did not show any alteration in crystallinity even after ANN at 50°C indicating that these are resistant to ANN. However, there were significant differences between ethanol-dehydrated potato starches and freeze-dried potato starches where freeze-drying decreased the potato starch crystallinity and changed the polymorphs (crystalline) from B-type to C-type (Fig. 1.1b) (Wang et al., 2017). Ji et al. investigated the ANN influence on waxy rice starch nanoparticles (SNPs) at 55°C for different time points which revealed Fourier transform infrared (FTIR) results of bands around 1047 and 1022 cm−¹ represents crystalline and amorphous structures, respectively. Fig. 1.1c represents this ratio of native and annealed SNPs. The ratio increased progressively with an increase in ANN time indicating that ANN improved the crystallinity of SNPs (Ji et al., 2019). Fig.1.1d-1.i depicts the endothermic peaks of both native and hydrothermally treated starch (Chakraborty et al., 2021).

Figure 1.1  Physicochemical characterization of annealed starch using (a) SEM, (b) XRD, (c) , and (d) DSC. (a) SEM images exhibit granular morphology of native and annealed wheat (W), yam (Y), potato (P), and ethanol dehydrated potato (EP) starches at 30, 40, and 50°C. (b) The XRD spectra of native and annealed starches. (i): wheat starch; (ii): Yam starch; (iii): Freeze-dried potato starch; (iv): Ethanol-dried potato starch. The (c) FTIR spectra show the effect of annealing for 6, 12, 24, and 48 hours on synthesized starch nanoparticles. (d) DSC thermograms depicting peak gelatinization temperatures of native and hydrothermally treated starch from (i) potato and (ii) brown rice. BRANN, annealed brown rice starch; BRHMT, heat moisture treated brown rice starch; BRN, native brown rice starch; PANN, annealed potato starch; PHMT, heat moisture treated potato starch; PSN, native potato starch. The images (a) and (b) were reproduced from Wang et al. (2017), with kind permission from (Elsevier). The image (c) was reproduced from Ji et al. (2019) with permission from (Elsevier). The image (d) was reproduced from Chakraborty et al. (2021) with permission from (John Wiley and Sons).

2.2.3. Heat moisture treatment

HMT is a hydrothermal modification technique that takes place at low moisture level (18%–27%), but at high temperatures i.e., above the gelatinization temperature (100°C) for an extended time interval (>16 hours) (Lawal, 2005). Factors such as gelatinization temperature, thermal stability, and susceptibility to α-amylase have been increased after HMT and these changes were due to the interplay of several aspects like the ratio between amylose and amylopectin, lipid–amylose complex, interactions among the starch chains, and arrangement of amylose chain inside the amorphous field (Kushwaha & Kaur, 2018, pp. 1–15). The influence of this technique on the physicochemical starch property brings about vital deviations in gelatinization, swelling ability, crystalline structure, retrogradation, and pasting properties (Hoover, 2010; Hormdok & Noomhorm, 2007). The size of the rice starch granule was found to increase post-HMT (Wang et al., 2018). Xing et al. conducted a study involving dual modification of corn starch through combined HMT treatment (15, 30, 60 minutes) and acid hydrolysis (AH, 6, 12, 24 hours) in various series (AH-HMT and HMT-AH), revealing that the AH-HMT sequence resulted in decreased swelling power, pasting viscosity, gelatinization enthalpy, and solubility compared to samples produced using the HMT-AH sequence (Xing et al., 2017). Results obtained by Gong et al. were similar, where the researchers investigated the effect of recurrent heat-moisture treatment (RHMT) and continuous heat-moisture treatment (CHMT) on red adzuki bean (Vigna angularis) starch that resulted in the decrease of pasting viscosities, swelling capacity, and solubility. SEM images revealed that starch of native red adzuki bean was oval or round with little fissures (Fig. 1.2a-A). Following the CHMT and RHMT, SEM images showed ruptured starch granules, and an increase in the number of scallops with more obvious starch disruption (Fig. 1.2a-H-L; B-G). As the treating time reached 10 hours (CHMT-10) and the circulation reached 4 times (RHMT-4), the granules began to aggregate (Fig. 1.2a-K; E). With the increase in CHMT and RHMT, the size of starch aggregation enlarged. The XRD results revealed that the NS has a C-type pattern with reflection intensities at angle 2θ values of 5.3, 15, 17, 18, and 23 degrees, and the relative crystallinity is 41.49%, whereas a change from C to A-type crystallinity was observed after RHMT-1 and CHMT-4 along with the disappearance of original peaks at 5.3 degrees (Fig. 1.2b). CHMT and RHMT-modified starches displayed lower relative crystallinity compared to NS. Increasing treatment time for CHMT and cycling times for RHMT led to a red-shift in FTIR spectra bands (Fig. 1.2c), indicating greater instability of functional groups without significant changes in peak viscosity. The DSC curve revealed starch after CHMT and RHMT had a broader gelatinization temperature and higher transition temperature range over NS (Fig. 1.2d). This suggests disruption of double-helical order, requiring a higher temperature for reorganization of the starch chains and water molecules. The decrease in gelatinization enthalpy indicated a reduction in double-helical order content due to gelatinization and partial disruption of starch granules (Gong et al., 2017). Buckwheat starch modified using HMT plays a major role in the prevention of chronic diseases. HMT is an effective modification technique that enhances the stability of starch and therefore can be used as a food ingredient in the production of low glycemic index food.

Figure 1.2  Physicochemical characterization heat moisture treated starch using (a) SEM, (b) XRD, (c) FTIR, and (d) DSC. (a) SEM images of native and different cycles of RHMT and CHMT starch samples (at ×1000 magnification). (A)-native starch; (B)-RHMT-1; (C)-RHMT-2; (D)-RHMT-3; (E)-RHMT-4; (F)-RHMT-5; (G)-RHMT- 6; (H)-CHMT-4; (I)-CHMT-6; (J)-CHMT-8; (K)-CHMT-10; (L)-CHMT-12. (b) X-ray diffraction patterns of native, RHMT and CHMT starch samples at a different number of cycles. (c) FT-IR spectra of native, RHMT and CHMT starch samples at different cycles. (d) DSC thermograms of native, RHMT and CHMT starch samples at different cycles. The images were reproduced from Gong et al. (2017), with permission from (Elsevier).

These techniques rely on specific temperature and moisture content over a period. ANN is preferred when the moisture level is excess or intermediate i.e., >60% or 40%–55%, respectively, whereas HMT is used when the moisture level is low (less than 35% w/w) (Chen et al., 2014). In a study by Adebowale et al., physical modification of red sorghum starch was carried out via ANN and HMT. Water absorption capacity increased for both modification techniques with a higher value seen in ANN starch, whereas oil absorption capacity increased for ANN starch but decreased for HMT starch due to the formation of lipophilic outer covering on the starch surface during ANN (Adebowale et al., 2005). In another study by Trung et al., colored sweet potato starch was modified using ANN and HMT and HMT-treated starch displayed reduced swelling and solubility in comparison to ANN-treated starch. Further, HMT treatment resulted in higher resistant starch (RS) content, credited to the increased stability of interactions between amylose-amylose and amylose-amylopectin chains during the treatment, indicating a more significant impact on RS compared to ANN (Trung et al., 2017).

2.3. Nonthermal treatments

2.3.1. Pulsed electric field

PEF is a nonthermal modification technique that aids in food preservation by killing pathogenic microorganisms and inactivating the enzymes, resulting in minimum loss of color, taste, nutrient, and texture (Han et al., 2009). It is a process that includes treating the liquid solution with electric pulses of high intensity (over 10 kV/cm) for a short period (≤40 μs) (Kushwaha & Kaur, 2018, pp. 1–15). Han et al. treated corn starch with PEF (up to 50 kV/cm). The SEM results showed damage and dissociation of starch granules under PEF treatment. Native corn starch granules had a smooth surface, with slight damage observed at 30 kV/cm and pits and aggregation at 40 kV/cm. At 50 kV/cm, most starch granules degraded and formed a gel-like structure. XRD analysis revealed a significant decrease in crystalline structure, with high-intensity PEF causing destruction of the crystalline region. A-type crystallinity was seen in native corn starch, characterized by primary peaks around 15, 17, 18, and 23 degrees (2Ɵ). While low-intensity PEF had minimal impact on the diffraction pattern, higher-intensity PEF caused a significant reduction in XRD peaks, indicating the destruction of the crystalline region (Fig. 1.3b) (Han et al., 2009). In a study by Qiu et al., the impact of PEF of strength 3 kV/cm on whole glutinous rice grains for 50–300 pulses was studied. The FTIR results revealed that the native and four PEF treated samples (50, 100, 200, 300 pulses) showed similar peak positions although stronger peak intensities were observed at 200 and 300 pulses PEF treatment. However, the similarity in the FTIR spectra of different rice samples indicated that neither new bonds nor chemical groups were added nor there was any molecular dissociation after PEF treatment (Fig. 1.3c) (Qiu et al., 2021). The DSC curve obtained from the study by Han et al., mentioned previously revealed that as electric field strength increased, gelatinization temperature and enthalpy decreased which was related to the crystalline region (Fig. 1.3d). In conclusion, PEF led to the rearrangement of the intragranular molecular structure of corn starch which must be further researched to find wide application in the food industry (Han et al., 2009; Hong et al., 2016).

Figure 1.3  Physicochemical characterization PEF treated starch using (a) SEM, (b) XRD, (c) FTIR, and (d) DSC. (a) SEM micrographs of corn starch treated at different electric field strength: (A) native; (B) 30 kV cm − ¹ ; (C) 40 kV cm − ¹ ; and (D) 50 kV cm − ¹ . (b) X-ray powder diffraction patterns of corn starch treated at different electric field strengths: (1) native; (2) 30 kV cm − ¹ ; (3) 40 kV cm − ¹ ; and (4) 50 kV cm − ¹ . (c) Separated and overlay Fourier transform infrared (FTIR) spectra (A) of control and PEF treated glutinous rice flour at the field strength of 3 kV/cm for 50, 100, 200, and 300 pulses. The overlay spectra have been zoomed to show the regions of 3500–2800 cm − ¹ (B), 1700–1500 cm − ¹ (C), and 1200–800 cm − ¹ (D). (d) DSC thermograms of gelatinization properties for PEF treated corn starch and native corn starch: (A) native; (B) 30 kV cm − ¹ ; (C) 40 kV cm − ¹ ; and (D) 50 kV cm − ¹ . The images (a), (b) and (d) were reproduced from Han et al. (2009) with permission from (Elsevier). The image (c) is reproduced from Qiu et al.