Microwave pretreatment promotes the annealing modification of rice starch

Effects of different pretreatment methods on the degree of substitution, structure, and physicochemical properties of synthesized malic acid sweet potato starch ester

BACKGROUND

The preparation of malic acid starch ester (MSE) is mostly carried out using a high temperature method, but there are problems such as high energy consumption, long preparation time, and uneven heating. Microwave technology can be used to overcome these limitations. The semi-crystalline structure of starch granules hinders the modifier's access to the matrix, thus limiting the esterification reaction. Physical techniques can act on the interior of the starch to create a number of active sites, thereby facilitating the reaction of the starch with esterification reagents. Therefore, this study investigated the effect of starch pretreatment by microwave, heat-moisture, and ultrasonic techniques on the degree of substitution (DS), structure, and physicochemical properties of MSE synthesized by the microwave method.

RESULTS

The DS of MSE was increased after pretreatments. The modified starch obtained by different pretreatment methods did not show new characteristic peaks, while the MSE synthesized showed new absorption peaks near 1735 cm-1. The granular structure and morphology of the modified starch obtained by microwave and heat-moisture pretreatment were gelatinized and aggregated, while some of the starch particles of the modified starch obtained by ultrasonic pretreatment appeared pore-sized. The relative crystallinity and gelatinization enthalpy of the MSE were reduced, but the crystallization pattern remained as A-type.

CONCLUSION

Overall, the results suggest that various pretreatment methods can enhance the DS of MSE by disrupting the structure of starch. The findings of this study provide theoretical support for improving the DS of esterified starch. © 2024 Society of Chemical Industry.

Improving physicochemical and nutritional attributes of rice starch through green modification techniques

Rice, has long been an inseparable part of the human diet all over the world. As one of the most rapidly growing crops, rice has played a key role in securing the food chain of low-income food-deficit countries. Starch is the main component in rice granules which other than its nutritional essence, plays a key role in defining the physicochemical attributes of rice-based products. However, rice starch suffers from weak techno-functional characteristics (e.g., retrogradability of pastes, opacity of gels, and low shear/temperature resistibility. Green modification techniques (i.e. Non-thermal methods, Novel thermal (e.g., microwave, and ohmic heating) and enzymatic approaches) were shown to be potent tools in modifying rice starch characteristics without the exertion of unfavorable chemical reagents. This study corroborated the potential of green techniques for rice starch modification and provided deep insight for their further application instead of unsafe chemical methods.

Structural and property changes of starch derivatives under microwave field: A review

Native starches are commonly modified for desired properties because of their limited applications. Among various modifications, microwave irradiation has been gaining strong interests and becoming a focal area to transform starch during the last few years. Such interests reside in microwave irradiation's high heating rates, lesser extent of loss in nutritional qualities, and so on when compared with other approaches. This review summaries the effects of microwave field on the structural (e.g. morphology characteristic, lamellae structure, crystallinity, and molecular structure) and physicochemical properties (e.g. pasting properties and gelatinization) of naturally existing starch derivatives. Different microwave-assisted chemical derivatizations can directly or indirectly affect starch structure from the macroscopic to the microscopic level, thereby resulting in various functionalities. Moreover, conventional starch modification processes can be optimized by applying microwave irradiation to obtain modified starch with high degree of substitution and low viscosity. The future research will help to better understand the structural changes of microwave-assisted starch chemical derivatization and thereby creating a wide range of functionalities.

Comprehensive review on single and dual modification of starch: Methods, properties and applications

Starch is a natural, renewable, affordable, and easily available polymer used as gelling agents, thickeners, binders, and potential raw materials in various food products. Due to these techno-functional properties of starch, food and non-food industries are showing interest in developing starch-based food products such as films, hydrogels, starch nanoparticles, and many more. However, the application of native starch is limited due to its shortcomings. To overcome these problems, modification of starch is necessary. Various single and dual modification processes are used to improve techno-functional, morphological, and microstructural properties, film-forming capacity, and resistant starch. This review paper provides a comprehensive and critical understanding of physical, chemical, enzymatic, and dual modifications (combination of any two single modifications), the effects of parameters on modification, and their applications. The sequence of modification plays a key role in the dual modification process. All single modification methods modify the physicochemical properties, crystallinity, and emulsion properties, but some shortcomings such as lower thermal, acidic, and shear stability limit their application in industries. Dual modification has been introduced to overcome these limitations and maximize the effectiveness of single modification.

Altering structure and enzymatic resistance of high-amylose maize starch by irradiative depolymerization and annealing with palmitic acid as V-type inclusion compound

This study explored a new physical modification approach to regulate enzymatic resistance of high-amylose starch for potentially better nutritional outcomes. High-amylose maize starch (HAMS) was subjected to chain depolymerization by electron beam irradiation (EBI), followed by inducing ordered structure through annealing in palmitic acid solution (APAS). APAS treatment significantly promotes the formation of ordered structure. Starch after the combinative modification showed up to 5.2 % increase in total crystallinity and up to 1.2 % increase in V-type fraction. The EBI-APAS modification led to increased gelatinization temperature (from 66.1 to 87.6 °C) and reduced final digested percentage under in vitro stimulated digestion conditions. The moderate extent of depolymerization resulted in higher enzymatic resistance, indicating that the extent of depolymerization is crucial in EBI-APAS modification. Pearson analysis showed a significant correlation between gelatinization onset temperature and digestion kinetic parameter (k1, rate constant of fast-phase digestion). Overall, the result suggests that ordered structures of degraded molecules induced by the combinative modification contribute to the enzymatic resistance of starch. This study sheds lights on future applications of EBI-APAS approach to regulate multi-scale structures and nutritional values of high-amylose starch.

Effects of Tremella fuciformis Mushroom Polysaccharides on Structure, Pasting, and Thermal Properties of Chinese Chestnuts (Castanea henryi) Starch Granules under Different Freeze-Thaw Cycles

The purpose of this study was to investigate the effect of Tremella fuciformis polysaccharides on the physicochemical properties of freeze-thawed cone chestnut starch. Various aspects, including water content, crystallinity, particle size, gelatinization, retrogradation, thermal properties, rheological properties, and texture, were examined. The results revealed that moderate freezing and thawing processes increased the retrogradation of starch; particle size, viscosity, shear type, hinning degree, and hardness decreased. After adding Tremella fuciformis polysaccharide, the particle size, relative crystallinity, and gelatinization temperature decreased, which showed solid characteristics. Consequently, the inclusion of Tremella fuciformis polysaccharide effectively countered dehydration caused by freezing and thawing, reduced viscosity, and prevented the retrogradation of frozen-thawed chestnut starch. Moreover, Tremella fuciformis polysaccharide played a significant role in enhancing the stability of the frozen-thawed chestnut starch. These findings highlight the potential benefits of incorporating Tremella fuciformis polysaccharides in starch-based products subjected to freeze-thaw cycles.

Recent progress in regulating starch digestibility using natural additives and sustainable processing operations

The development of a healthier and more sustainable food supply is a main concern of consumers, industry, governments, and international institutions. Foods containing high levels of rapidly digestible starches have been linked to a rise in the number of people suffering from diet-related chronic diseases. Consequently, there is interest in reducing the digestibility of starch to improve their healthiness. The ability of natural additives including proteins, dietary fibers, and polyphenols, and sustainable processing technologies such as high-intensity ultrasonic, pulsed electric field, non-thermal plasma, γ-ray irradiation that regulate reduce starch digestibility in foods are reviewed. The potential mechanisms of action, advantages, and disadvantages of each approach at inhibiting starch digestibility is highlighted. The potential for commercializing these technologies is discussed, and areas where further research are required are emphasized. Natural additives and sustainable processing operations can effectively reduce the digestibility of starch and inhibit postprandial sugar "spikes" in the bloodstream by adjusting the structural changes, which can be used to create healthier and more sustainable foods and have broad application prospects.

Insight into how E-beam pretreatment promotes sodium hypochlorite oxidation for structure-property improvement of cassava starch: A molecular-level modulation mechanism

To investigate the role of E-beam treatment on the structure-properties of oxidized starch, this study investigated the influence of E-beam (1, 3, 6 kGy) pretreatment combined with NaClO oxidation (1% and 3%) on the multi-scale structural, physicochemical, and digestive properties of cassava starch. Results showed that E-beam treatment did not affect the starch surface, but the oxidative modification increased granule surface roughness. Also, the synergistic modification preserved starch growth rings, FT-IR patterns and crystal types. Further investigations revealed that E-beam induced starch molecular degradation, leading to decreased molecular weight, depolymerization of long chains, and a loss of short-range order. Moreover, oxidation treatment exacerbated the disruption in starch molecular structure, as evidenced by crystallinity loss, viscosity, and enthalpy reduction. Notably, E-beam induces starch yellowing; however, oxidative modification increases starch whiteness. Additionally, the synergistic modification improved native starch's lower solubility and enhanced the resistant starch content. Results suggest that E-beam pretreatment can enhance oxidative modification by promoting the exposure of active sites of starch molecules without destroying starch structure and can be considered an advanced, green, and efficient pretreatment for modified starch in the future.

Ionizing and nonionizing radiations can change physicochemical, technofunctional, and nutritional attributes of starch

Challenges for the food/non-food applications of starch mostly arise from its low stability against severe processing conditions (i.e. elevated temperatures, pH variations, intense shear forces), inordinate retrogradability, as well as restricted applicability. These drawbacks have been addressed through the modification of starch. The escalating awareness of individuals toward the presumptive side effects of chemical modification approaches has engrossed the attention of scientists to the development of physical modification procedures. In this regard, starch treatment via ionizing (i.e. gamma, electron beam, and X-rays) and non-ionizing (microwave, radiofrequency, infrared, ultraviolet) radiations has been introduced as a potent physical strategy offering new outstanding attributes to the modified product. Ionizing radiations, through dose-dependent pathways, are able to provoke depolymerization or cross-linking/grafting reactions to the starch medium. While non-ionizing radiations could modify the starch attributes by changing the morphology/architecture of granules and inducing reorientation/rearrangement in the molecular order of starch amorphous/crystalline fractions.

Structural, rheological, pasting, and digestive properties of wheat A-starch: Effect of outshell removal combined with annealing

Wheat A- starch was subjected to single and combined CaCl₂ and annealing (ANN) treatments. The influence of the treatment on wheat A- starch's structural, rheological, pasting, and digestive characteristics were studied. The results indicated that the application of CaCl₂ treatment caused the removal of the outer layer of wheat A-starch, disrupted the integrity of the growth ring structure, and lowered the molecular weight of amylopectin and relative crystallinity. Meanwhile, the application of outshell removal combined with ANN treatment led to significant damage to the starch granules, resulting in a marked reduction in relative crystallinity, as well as the molecular weight of amylopectin and amylose. However, no changes were found in the non-Newtonian pseudoplastic behavior of starch after single or combined treatments. Furthermore, the combination of outshell removal and annealing treatment resulted in a decreased peak viscosity as well as trough viscosity of starch. Moreover, long-time ANN treatment had the potential to improve the resistant starch (RS) content of deshell starch.

Microstructural, physicochemical properties and starch digestibility of brown rice flour treated with extrusion and heat moisture

Effects of heat moisture treatment (HMT), extrusion treatment (ET), and the combination treatment (HMT-ET) on microstructural, physicochemical properties, and starch digestibility of brown rice flour (BRF) were investigated. With a rise in resistant starch (RS), melting temperature, and a decrease in swelling capacity (SC), peak viscosity, and apparent amylose content (AAC), the HMT-ET BRF showed a significant lower expected glycemic index (eGI) than HMT and ET. XRD and FTIR results showed ET, HMT-ET caused the transition of starch crystals from amorphous to crystalline region, suggesting the formation of the starch-lipid complex. The analysis of DSC and RVA proved HMT-ET flours induced starch gelatinization and inhibited the starch retrogradation of BRF compared with the other three flours. Correlation analysis suggested that the combined effect of HMT and ET was response for the changes in physicochemical properties and reduction of in vitro starch digestibility. Overall, the BRF after HMT-ET with improved physicochemical properties and starch digestibility could be better utilized as a good substitute for carbohydrate sources.

Designing liquefaction and saccharification processes of highly concentrated starch slurry: Challenges and recent advances

Starch-based sugars are an important group of starch derivatives used in food, medicine, chemistry, and other fields. The production of starch sugars involves starch liquefaction and saccharification processes. The production cost of starch sugars can be reduced by increasing the initial concentration of starch slurry. However, the usage of the highly concentrated starch slurry is characterized by challenges such as low reaction efficiency and poor product performance during the liquefaction and saccharification processes. In this study, we endeavored to provide a reference guide for improving high-concentration starch sugar production. Thus, we reviewed the effects of substrate concentration on the starch sugar production process and summarized several potential strategies. These regulation strategies, such as physical field pretreatment, complex enzyme-assisted, and temperature control, can significantly increase the starch concentration and mitigate the challenges of using highly concentrated starch slurry. We believe that highly concentrated starch sugar production will achieve a qualitative leap in the future. This review provides theoretical guidance and highlights the importance of high concentration in starch-based sugar production. Further studies are needed to explore the fine structure and enzyme attack mode during the liquefaction and saccharification processes to regulate the production of more targeted products.

Cassava starch and chickpea flour pre-treated by microwave as a substitute for gluten-free bread additives

There is an increasing demand for gluten-free products, which are regularly made by a combination of ingredients and additives. Microwave pre-treatment of gluten-free ingredients is an alternative to food additives because it may induce changes in protein and starch functional properties. In this context, this study aimed to apply microwave treatment in cassava starch and chickpea flour, analyzing their functional and thermal properties and their ability to substitute additives in gluten-free breads, comparing them to an additive-containing bread. All formulations were analyzed regarding their physical characteristics and quality parameters. The microwave-treated ingredients showed color, thermal properties and morphology changes. The bread made with chickpea flour treated with initial moisture of 40% showed the best quality parameters when compared to the control bread. The ingredients pre-treated with microwave have shown efficiency on gluten-free bakery additives substitution, allowing the use of a clean label terminology.

Insights on Some Polysaccharide Gel Type Materials and Their Structural Peculiarities

Global resources have to be used in responsible ways to ensure the world's future need for advanced materials. Ecologically friendly functional materials based on biopolymers can be successfully obtained from renewable resources, and the most prominent example is cellulose, the well-known most abundant polysaccharide which is usually isolated from highly available biomass (wood and wooden waste, annual plants, cotton, etc.). Many other polysaccharides originating from various natural resources (plants, insects, algae, bacteria) proved to be valuable and versatile starting biopolymers for a wide array of materials with tunable properties, able to respond to different societal demands. Polysaccharides properties vary depending on various factors (origin, harvesting, storage and transportation, strategy of further modification), but they can be processed into materials with high added value, as in the case of gels. Modern approaches have been employed to prepare (e.g., the use of ionic liquids as "green solvents") and characterize (NMR and FTIR spectroscopy, X ray diffraction spectrometry, DSC, electronic and atomic force microscopy, optical rotation, circular dichroism, rheological investigations, computer modelling and optimization) polysaccharide gels. In the present paper, some of the most widely used polysaccharide gels will be briefly reviewed with emphasis on their structural peculiarities under various conditions.

Prevents kudzu starch from agglomeration during rapid pasting with hot water by a non-destructive superheated steam treatment

Superheated steam (SST) at different moisture contents (10% ∼ 30%) was used to prevent the agglomeration of kudzu starch during rapid pasting with hot water. Changes in pasting-related properties and multi-scale structures were investigated. At moisture content of 20%, SST dramatically reduced the agglomeration rate from 42.20% to 2.97% without destroying the microstructure of kudzu starch or deteriorating the rheological properties of kudzu starch paste, which was superior to the conventional pre-gelatinization treatment. The agglomeration was prevented mainly by decreasing the swelling power and increasing the pasting temperature of kudzu starch. The slight disruption of multi-scale structures may facilitate faster water absorption by kudzu starch, but it was not the primary prevention mechanism. Moreover, the solubility of kudzu starch was not related to the agglomeration, since it was significantly decreased by SST. Our findings could provide new insights into the rapid pasting of starchy powders or flours with hot water.

Physicochemical, Pasting Properties and In Vitro Starch Digestion of Chinese Yam Flours as Affected by Microwave Freeze-Drying

Microwave freeze-drying (MFD) is a new freeze-drying technique, which differs from single microwave treatment; it involves simultaneous effects of microwave power, time, and the moisture state applied to the materials. In this study, the effects of MFD under various microwave power densities (0.5, 1.0, and 1.5 W/g) on the drying characteristics of Chinese yam slices and the physicochemical, pasting, and thermal properties as well as the starch digestibility of the flour were investigated using conventional hot air drying (HAD) at 50 °C as a control. Compared to HAD, MFD shortened the drying time up to 14.29~35.71%, with a higher drying efficiency at a high microwave power density (1.5 W/g). MFD yam flours provided benefits over HAD products in terms of color, water/oil absorption capacity, and solubility, exhibiting high hot-paste viscosity but low resistant starch content. The content of total starch and free glucose of the yam flour and its iodine blue value were significantly influenced by the drying method and the MFD process parameters (p < 0.05). MFD processing could disrupt the short-range ordered structure of yam starch. Among the MFD flours, samples dried by MFD at 1.5 W/g presented the highest ratio of peak intensity at 1047 and 1022 cm−1 (R1047/1022) value, gelatinization enthalpy, and resistant starch content. These results gave a theoretical foundation for the novel freeze-drying method that MFD applied to foods with a high starch content, enabling the production of a product with the desired quality.

Effects of Biodegradation of Corn-Starch-Sodium-Alginate-Based Liquid Mulch Film on Soil Microbial Functions

In response to the problems of the poor degradability and mechanical properties of liquid mulch, natural non-toxic polymer compound corn starch and sodium alginate were used to prepare fully biodegradable liquid mulch. The preparation conditions of the mulch were optimized, and the mechanical properties of the mulch and the changes in the microbial community in soil with the mulch degradation were analyzed. The corn-starch–sodium-alginate-based liquid mulch film had an optimum performance at a tensile strength of 0.145 MPa and an elongation at a break of 16.05%, which was attained by adding 33.33% sodium alginate, 50% glycerol 22 and 4% citric acid to corn starch after moist heat modification. Fourier transform infrared spectroscopy analysis showed that the -COOH in sodium alginate could interact with the -OH in starch and glycerol through hydrogen bonding, thus, resulting in a denser structure and better mechanical properties of the liquid mulch as a non-crystalline material. The soil burial degradation study of mulch revealed that corn-starch–sodium-alginate-based liquid mulch degraded completely at 25 days macroscopically, and mulch degradation increased soil organic matter content. Microbial kinetic analysis showed that the abundance and diversity of the bacterial community decreased with the degradation of the mulch, which was conducive to the optimization of the bacterial community structure and function. Arthrobacter of the class Actinomycetes became the dominant microorganism, and its abundance increased by 16.48-times at 14 days of mulch degradation compared with that before degradation, and Acidophilus phylum (14 days) decreased by 99.33%. The abundance of fungal communities was elevated in relation to the main functional microorganisms involved in liquid mulch degradation, with Alternaria and Cladosporium of the Ascomycete phylum Zygomycetes being the most active at the early stage of mulch degradation (7 days), and the relative abundance of Blastocystis was significantly elevated at the late stage of mulch degradation (14 days), which increased by 13.32%. This study provides important support for the green and sustainable development of modern agriculture.

Ultrasound-chilling assisted annealing treatment to produce a lower glycemic index of white rice grains with different amylose content

White rice samples, Chai-Nat1 (CN1) and Jasmin rice (KDML105), were treated with the ultrasound-chilling (UC) and combined with annealing treatments (UC + ANN 45, UC + ANN50, and UC + ANN55). Their physicochemical properties and in vitro glycemic index of rice samples were analyzed. UC + ANN treatments presented pasting temperature, gelatinization temperature and crystallinity increased whereas the glycemic index of both rice samples was decreased as compared to its native. Especially, UC + ANN55 treated rice produced the lowest glycemic index and starch hydrolysis. Moreover, UC + ANN treated CN1 rice exhibited delayed gelatinization temperature, increased gelatinization enthalpy, and decreased glycemic index than KDML105 rice. In addition, Pearson's correlation presented that UC + ANN and amylose content had a highly negative correlation with the glycemic index at p < 0.0.1. The result exhibited that UC followed by ANN show an effective way to modify starch granules with delayed starch hydrolysis reduced glycemic index and properties depending on annealing temperature and rice cultivar.

Physicochemical Properties and Digestion Resistance of Acetylated Starch Obtained from Annealed Starch

One of the examples of physical starch modifications is the retention of a starch suspension in water having a temperature slightly lower than the pasting temperature (annealing). The aim of this study was to investigate the effect of the annealing process performed at various temperatures as the first stage of starch modification. The annealed starch preparations were then esterified using acetic acid anhydride. Finally, the annealed and acetylated starch preparations were determined for their properties. The annealing of starch before acetylation triggered changes in the properties of the modified preparations. It contributed to a higher degree of starch substitution with acetic acid residues and to the increased swelling power of starch. Both these properties were also affected by the annealing temperature. The highest resistance to amylolysis was found in the case of the starch preparation annealed at 53.5 °C and acetylated. The double modification involving annealing and acetylation processes increased the onset and end pasting temperatures compared to the acetylation alone. Similar observations were made for the consistency coefficient and yield point.

Physical modification of starch by heat-moisture treatment and annealing and their applications: A review

Heat-moisture treatment (HMT) and annealing are hydrothermal starch modifications. HMT is performed using high temperature and low moisture content range, whereas annealing uses excess of water, a long period of time, and temperature above the glass transition and below the gelatinization temperature. This review focuses on: research advances; the effect of HMT and annealing on starch structure and most important properties; combined modifications; and HMT-starch and annealed-starch applications. Annealing and HMT can be performed together or combined with other modifications. These combinations contribute to new applications in different areas. The annealed and HMT-starches can be used for pasta, candy, bakery products, films, nanocrystals, and nanoparticles. HMT has been studied on starch digestibility and promising data have been reported, due to increased content of slowly digestible and resistant starches. The starch industry is in constant expansion, and modification processes increase its versatility, adapting it for different purposes in food industries.

Structural and physicochemical properties of lotus seed starch-chlorogenic acid complexes prepared by microwave irradiation

Lotus seed (LS) has a high starch content and possesses many useful functional properties, which are mainly attributed to its phenolic compound content. The objective of this study was to investigate the effect of microwave irradiation (MW) treatment on the structural and physicochemical properties of a lotus seed starch-chlorogenic acid (CA) blend. MW treatment appeared to promote the formation of LS-CA complexes and the modified starch displayed more rougher structures than native starch. The particle size distribution of starch remained approximately constant when the microwave power was 200 W, but increased sharply with further increases in microwave power; a similar trend was observed in the swelling and solubility of starch. XRD and FT-IR spectra show that MW treatment degraded the ordered crystalline structure of starch, facilitating exposure of the starch chains originally buried in the crystalline and amorphous regions within the grains. During this treatment, CA interacted with starch molecules by hydrogen bonding and form a LS-CA complex, which inhibited the self-assembly process of starch chains. These findings demonstrated the potential use of MW treatment in controlling the storage and processing quality of lotus seed, or other starchy foods rich in polyphenols.

Physicochemical property changes and aroma differences of fermented yellow pea flours: role of Lactobacilli and fermentation time

The aim of this study was to evaluate the physicochemical properties and aroma differences of yellow pea flours fermented by five lactic acid bacteria (LAB) strains including two Lactiplantibacillus, two Lactobacillus, and one Lacticaseibacillus with different fermentation time. The cell population and the pH of pea flour slurry, as well as the proximate chemical composition, amino acids, thermal and pasting properties, surface morphology, and aromatic differences of fermented flours were characterized. The cell population of all strains except for Lactobacillus helveticus was observed to reach above 107 CFU mL-1 after 24 h of fermentation. The fermentation with Lactobacilli resulted in the increase of amino acids and ash contents, and the reduction of fat content. Rapid viscosity analysis indicated that short time (18 h) fermentation with L. helveticus drastically improved the pasting properties of the flours by facilitating starch granule expansion. The aromatic compounds of the fermented yellow pea flours were highly reliant on the strains and fermentation time. The untargeted metabolomics analysis with the aid of multivariate data analysis can discriminate the aroma differences among the fermented yellow pea flours. L. acidophilus fermentation led to the production of three aromatic compounds which may contribute to an improved aromatic profile.

Effect of Thermal and Non-Thermal Processing on the Nutritional Composition, Pasting Profile and Protein Secondary Structure of Alfalfa

Alfalfa is an unconventional alternative legume and its potentiality for utilization can be improved by processing. In this study, alfalfa seeds were processed by different thermal and non-thermal techniques and evaluated for their physical properties, colour characteristics, nutritional composition, pasting profile and protein secondary structure. The results were analyzed using Principal Component Analysis to elucidate the effect of processing. Colour of the flour was more affected by thermal processing in comparison to non-thermal processing. Nutritional composition of alfalfa flour was significantly affected by germination as compared to other methods and germinated flour showed an increase in the protein content. All the processing treatments resulted in improving the pasting properties except for germination. Particularly, marked improvement in the pasting properties was observed by wet heat processing and soaking. ATR-FTIR exhibited change in the secondary structure of the protein as a result of processing and showed the dominance of intermolecular β-sheets in extrusion, germination and microwave treated flour and formation of anti-parallel β-sheets after dry heat processing. Wet heat processing and soaking treatment can be employed for alfalfa for enhancing its techno-functionality.

Physicochemical and digestive properties of A- and B-type granules isolated from wheat starch as affected by microwave-ultrasound and toughening treatment

In this study, the effect of microwave-ultrasound or/and toughening treatment on the physicochemical, structural properties, and in vitro digestibility of A- and B-type granules isolated from wheat starch were investigated. From the SEM, microwave-ultrasound and toughening treatment (MU-T) led to the appearance of irregular and disrupted structure significantly and an increment in the resistant starch content of A- and B-type granule. Furthermore, the MU-T starch possessed the lowest swelling power, light transmittance, and gelatinization temperature range (T_c -T_o) and the highest ΔH. After MU-T, the relative crystallinity (RC) of X-ray pattern, Fourier transform infrared ratio of 1047/1022 cm^-1, and the content of double helix and single helix of ¹³C CP/MAS NMR had increased significantly. In particular, there was a difference in the content of RS and SDS between A-starch granules and B-starch granules as well as their changes after modification (from 69.305% to 82.93 for A-starch and form 74.97% to 88.17 for B-starch, respectively), which was a similar trend with RC and helix content. This study indicated that, for both A-type granule and B-type granule starches, microwave-ultrasound and toughening treated samples had unique properties compared to singly modified starches.

A review on the physicochemical properties of starches modified by microwave alone and in combination with other methods

Native starches are unsuitable for most industrial applications. Therefore, they are modified to improve their application in the industry. Starch may be modified using enzymatic, genetic, chemical, and physical methods. Due to the demand for safe foods by consumers, researchers are focusing on the use of cheap, safe and environmentally friendly methods such as the use of physical means for starch modification. Microwave heating of starch is a promising physical method for starch modification due to its advantages such as homogeneous operation throughout the whole sample volume, shorter processing time, greater penetration depth and better product quality. More recently, the use of synergistic methods for starch modification is being encouraged because they confer better functionality on starch than single methods. This review summarizes the present knowledge on the structure and physicochemical properties of starches from different botanical origins modified using microwave heating alone and in combination with other starch modification methods.

Accelerated aging of rice by controlled microwave treatment

To obtain the desired technological properties (pasting, texture, and rheology) of naturally aged rice (AR), the aging process of freshly harvested rice was accelerated by controlled microwave treatment at 540 W for 1-3 min. Similar to AR, the rice microwave treated for 2 min showed increased pasting viscosities (peak, trough, breakdown, final, and setback) and pasting temperature, enhanced gel hardness and strength, and reduced gel adhesiveness. The mechanism by which microwaves accelerated rice aging was illustrated. Microwave treatment promoted the formation of protein disulfide bonds and the release of free phenolic acids, which enhanced protein gel network and cell wall strength. This phenomenon inhibited the swelling of starch granules and consequently modified the technological properties of rice. The crystalline structure and fatty acid content of rice flour was uninvolved in the mechanism, but the microwave-induced micromechanical change (intercellular cleavage to intracellular cleavage) of rice endosperm may be involved.