Hierarchical structure and slowly digestible features of rice starch following microwave cooking with storage

Preparation of debranched starch with high thermal stability and crystallinity using a novel thermal cycling treatment

Herein, the effects of temperature cycling (4 °C/50 °C/100 °C) on the recrystallization, physicochemical properties, and digestibility of debranched starch (DBS) were investigated. Temperature cycling involved heating DBS to 100 °C to dissociate weak heat-sensitive crystalline structures and cooling to 4 °C to induce the rapid growth of crystal nuclei, followed by maintaining the temperature at 50 °C to promote orderly crystalline growth. This procedure aimed to increase the degree of crystalline structure in recrystallized DBS, thereby resulting in DBS that was heat- and digestion-resistant. Temperature cycling increased the dissociation temperature of DBS, and temperatures of up to 114.8 °C were attained after five cycling times. With increasing cycles, the crystalline structure of DBS transitioned from B-type to the more robust and compact A-type, and the crystallinity increased to ∼81.9 % (after seven cycles). Raman and Fourier transform infrared (FTIR) spectra indicated that temperature cycling enhanced the short-range ordered structure of DBS. Moreover, in vitro digestion experiments demonstrated that the resistant starch content of DBS increased to ∼61.9 % after eight cycles. To summarize, this study demonstrated a green and effective method for preparing heat-and digestion-resistant recrystallized DBS, which can be used for developing dietary supplements and low gastrointestinal staples.

Exploring the remarkable effects of microwave treatment on starch modification: From structural evolution to changed physicochemical and digestive properties

As one of the crucial components of the food system, starch can be hydrolyzed into glucose after gastrointestinal digestion, so regulating its digestive properties is vital for maintaining health. Microwaves can promote the rearrangement of intramolecular structure of starch, thus improving its physicochemical properties, enhancing its slowly digestible features, and expanding its scope of application. This review zooms in describing recent research results concerning the effects of microwave treatment on the multi-scale structure and physicochemical properties of starch and summarizing the patterns of these changes. Furthermore, the changes in starch structure, resistant starch content, and glycemic index after digestion are pointed out to gain an insight into the enhancement of starch slowly digestible properties by microwave treatment. The resistance of starch to enzymatic digestion may largely hinge on the specific structures formed during microwave treatment. The multi-level structural evolutions of starch during digestion endow it with the power to resist digestion and lower the glycemic index. The properties of starch dictate its application, and these properties are highly associated with its structure. Consequently, understanding the structural changes of microwave-modified starch helps to prepare modified starch with diversified varieties and functional composites.

Structural features of rice starch-protein system: Influence of retrogradation time and quick-freezing temperature

This work investigated the effect of retrogradation time (0 h, 2 h, 4 h, 6 h, 8 h) and freezing temperature (-20 °C, -32 °C, -80 °C) on the muti-scale structures of the rice starch-protein system of quick-frozen wet rice noodles. The Relative crystallinity and porosity of the rice starch-protein system increased with increasing retrogradation time. However, while longer retrogradation does lead to an improvement in relative crystallinity, it also results in significant damage to the microstructure. When the retrogradation time was 6 h, the microstructure of the rice starch-protein system was less damaged and the quality was better. The mass fractal dimension and relative crystallinity of the rice starch-protein system exhibited an increase as the freezing temperature was decreased from -20 to -80 °C. Additionally, the retrogradation degree of starch decreased, the size of ice crystals decreased, and the disruption of microforms was reduced. The muti-scale structures of the rice starch-protein systems were similar when quick-frozen at temperatures of -32 and -80 °C. Therefore, the optimal treatment method for practical production is to quick-freeze at -32 °C and age for 6 h to obtain high-quality quick-frozen wet rice noodles.

A Comprehensive Study on the Influence of Superheated Steam Treatment on Lipolytic Enzymes, Physicochemical Characteristics, and Volatile Composition of Lightly Milled Rice

Enzyme inactivation is crucial for enhancing the shelf life of lightly milled rice (LMR), yet the impact of diverse superheated steam (SS) treatment conditions on lipolytic enzyme efficiency, physicochemical properties, and volatile profiles of LMR remains unclear. This study investigated varying SS conditions, employing temperatures of 120 °C, 140 °C, and 160 °C and exposure times of 2, 4, 6, and 8 min. The research aimed to discern the influence of these conditions on enzyme activities, physicochemical characteristics, and quality attributes of LMR. Results indicated a significant rise in the inactivation rate with increased treatment temperature or duration, achieving a notable 70% reduction in enzyme activities at 120 °C for 6 min. Prolonged exposure to higher temperatures also induced pronounced fissures on LMR surfaces. Furthermore, intensive SS treatment led to a noteworthy 5.52% reduction in the relative crystallinity of LMR starch. GC/MS analysis revealed a consequential decrease, ranging from 44.7% to 65.7%, in undesirable odor ketones post-SS treatment. These findings underscore the potential of SS treatment in enhancing the commercial attributes of LMR.

Insight into the improvement in pasting and gel properties of waxy corn starch by critical melting treatments

To improve the pasting and gel properties of waxy corn starch (WCS), the native starch was modified by critical melting (CM) at the onset temperature (TO), peak temperature (TP), and conclusion temperature (TC) (labeled CMO, CMP, and CMC respectively). CM treatments significantly enhanced the thermal stability of the WCS, as indicated by the increase in the peak gelatinization temperature, pasting temperature, and peak time. In addition, after CMP treatment, the storage modulus, hardness, gumminess, springiness, and chewiness of starch gels significantly increased by 43.29 %, 31.14 %, 23.36 %, 8.26 %, and 61.43 %, respectively, and the syneresis rate significantly decreased by 19.69 % (p < 0.05). These results indicated that CMP treatments significantly improved the gelling ability and freeze-thaw stability of the WCS. These results are ascribed to the partial disruption and enhanced rearrangement of the starch crystalline structure. CMP treatment induced the crystalline structure of starch to be partially disrupted and a hard structure was formed on the surface of starch granules. The hard structure in CMP-treated starch supplied more attachment points for crystalline structure rearrangement during gelatinization. Therefore, the above results indicated that CMP treatments can be used to modify starch to improve the pasting and gel properties of starch-based food products.

Effect of starch-protein interaction on regulating the digestibility of waxy rice starch under radio frequency treatment with added CaCl2

This study investigated the effect of starch-protein interaction on regulating the digestibility of waxy rice starch under radio frequency (RF) treatment with added salts. The results showed that starch-protein interactions could significantly reduce the digestibility of waxy rice starch (WRS) under synergetic Ca²⁺-RF treatment. With the increase of Ca²⁺ content (0-2 %), the resistant starch content of WRS-WPI, WRS-SPI and WRS-PPI increased from 35.53 %, 36.12 % and 38.78 % to 51.05 %, 52.82 % and 55.93 %, respectively. The addition of appropriate Ca²⁺ content could increase the short-range ordered structure and lamella structure and form a more compact and uniform microstructure. In addition, the interaction between WRS and protein was mainly through hydrogen bonding and hydrophobic interactions during RF treatment. Furthermore, the presence of Ca²⁺ could improve the distribution and mobility of water molecules and regulate the rheological properties of WRS-protein complexes. This study offers theoretical guidance for the design and production of rice starch-based products with lower digestibility.

Non-destructive characterization of pulse flours-A review

The consumption of plant-based proteins sourced from pulses is sustainable from the perspective of agriculture, environment, food security, and nutrition. Increased incorporation of high-quality pulse ingredients into foods such as pasta and baked goods is poised to produce refined food products to satisfy consumer demand. However, a better understanding of pulse milling processes is required to optimize the blending of pulse flours with wheat flour and other traditional ingredients. A thorough review of the state-of-the-art on pulse flour quality characterization reveals that research is required to elucidate the relationships between the micro- and nanoscale structures of these flours and their milling-dependent properties, such as hydration, starch and protein quality, components separation, and particle size distribution. With advances in synchrotron-enabled material characterization techniques, there exist a few options that have the potential to fill knowledge gaps. To this end, we conducted a comprehensive review of four high-resolution nondestructive techniques (i.e., scanning electron microscopy, synchrotron X-ray microtomography, synchrotron small-angle X-ray scattering, and Fourier-transformed infrared spectromicroscopy) and a comparison of their suitability for characterizing pulse flours. Our detailed synthesis of the literature concludes that a multimodal approach to fully characterize pulse flours will be vital to predicting their end-use suitability. A holistic characterization will help optimize and standardize the milling methods, pretreatments, and post-processing of pulse flours. Millers/processors will benefit by having a range of well-understood pulse flour fractions to incorporate into food formulations.

Starch intrinsic crystals affected the changes of starch structures and digestibility during microwave heat-moisture treatment

The structural and functional changes of starch during hydrothermal treatment are influenced by its intrinsic properties. However, how the intrinsic crystalline structures of starch affect changes in structure and digestibility during microwave heat-moisture treatment (MHMT) has not been well understood. In this study, we prepared starch samples with varying moisture content (10 %, 20 %, and 30 %) and A-type crystal content (4.13 %, 6.81 %, and 16.35 %) and investigated the changes in their structures and digestibility during MHMT. Results showed that starch with a high A-type crystal content (16.35 %) and moisture levels of 10 % to 30 % exhibited less ordered structures after MHMT, while starches with lower A-type crystal content (4.13 % to 6.18 %) and moisture content of 10 % to 20 % showed more ordered structures after treatment; but less ordered structures when the moisture content was 30 %. All starch samples had lower digestibility after MHMT and cooking; however, starches with lower A-type crystal content (4.13 % to 6.18 %) and moisture content of 10 % to 20 % displayed significantly lower digestibility after treatment compared to modified starches. Accordingly, starches contained content of A-type crystals of 4.13 %-6.18 % and moisture of 10 %-20 % potentially had better reassembly behaviors during the MHMT to slow starch digestibility in a larger magnitude.

Effects of Reheating Methods on Rheological and Textural Characteristics of Rice Starch with Different Gelatinization Degrees

Pregelatinized starch (PGS) is often used to improve the processing quality of foodstuffs, but little attention has been paid to the effects of different reheating methods and degree of starch gelatinization (DSG) on their rheological and textural properties. In this study, pregelatinized rice starches (RS) with gelatinization degrees ranging from 58% to 100% were prepared via different Rapid Visco Analyser (RVA) heating procedures and reheated in various methods, including high-power microwave (HM), low-power microwave (LM), and water bath. The rheological behavior and textural properties were explored, and the results demonstrated that the consistency, gel strength, hardness, and springiness of PGS in all tested samples decreased significantly after reheating. The storage modulus (G') of PGS increased dramatically while the thermal stability decreased. Interestingly, the reheating methods possessed various effects on the starch of different DSG.

Insight into the incredible effects of microwave heating: Driving changes in the structure, properties and functions of macromolecular nutrients in novel food

Microwave heating technology performs the characteristics of fast heating, high efficiency, green energy saving and easy control, which makes it deeply penetrate into the food industry and home cooking. It has the potential to alter the appearance and flavor of food, enhance nutrient absorption, and speed up the transformation of active components, which provides an opportunity for the development of innovation foods. However, the change of food driven by microwave heating are very complex, which often occurs beyond people's cognition and blocks the development of new food. It is thus necessary to explore the transformation mechanism and influence factors from the perspectives of microwave technology and food nutrient diversity. This manuscript focuses on the nutritional macromolecules in food, such as starch, lipid and protein, and systematically analyzes the change rule of structure, properties and function under microwave heating. Then, the flavor, health benefits, potential safety risks and bidirectional allergenicity associated with microwave heating are fully discussed. In addition, the development of new functional foods for health needs and future market based on microwave technology is also prospected. It aims to break the scientific fog of microwave technology and provide theoretical support for food science to understand the change law, control the change process and use the change results.

Physical modification of maize starch by gelatinizations and cold storage

The effects of gelatinization at three selected temperatures (DSC characteristic peaks temperature: TO, TP, and TC) and subsequent cold storage (CS) treatment on structural characteristics, pasting, and rheological properties of maize starch (MS) were investigated. The pasting, rheological properties of MS was changed with the increase of gelatinization temperature from TO to TC, but were not further significantly changed if the gelatinization temperature was higher than TC. Pasting and thermal properties analysis suggested that gelatinization at TC (TC treatment) significantly increased the gelatinization and pasting temperature of MS. Moreover, TC treatment decreased breakdown viscosity by 8.49 times and setback viscosity by 2.53 times. Dynamic rheological measurements revealed that the TC treatment caused the lower G' and G" of MS, and decreased the thickening coefficient by 55.17 %. These results indicated that TC treatment could enhance the thermal stability properties of MS, inhibiting the shear and short-term retrogradation, the shear-thinning behavior of MS. Interestingly, the CS treatment further inhibited the shear and short-term retrogradation and the shear-thinning behavior of MS. The leaked starch molecules aggregate to form a harder structure after gelatinization and starch molecules were further aggregated after CS treatment, these all were hypothesized to be responsible for these results.

Pea-Resistant Starch with Different Multi-scale Structural Features Attenuates the Obesity-Related Physiological Changes in High-Fat Diet Mice

The present study compared the modulatory effects of different resistant starches (RSs) isolated from native (NP-RS), acid-hydrolyzed (AHP-RS), and pullulanase debranched (PDP-RS) pea starches on the corresponding in vivo metabolic responses in high fat (HF)-diet-induced obese mice. The biochemical studies on serum lipid profile and antioxidant enzyme activities were supported by histological and gene expression analyses, which suggested a potential therapeutic role for RS in regulating obesity, possibly through the production of short-chain fatty acids and the proliferation of some beneficial colonic bacteria, including Allobaculum, Bifidobacterium, Odoribacter, Clostridium, and Prevotella. Particularly, a more pronounced effect of AHP-RS with a higher proportion of the crystalline region and a more ordered double-helical alignment on improving the hyperlipidemic symptoms in obese mice induced by a HF diet was observed. Our analysis revealed that the RS3 samples seemed to be more effective than RS2 in terms of attenuating obesity in mice that were fed a HF diet.

Appropriate microwave improved the texture properties of quinoa due to starch gelatinization from the destructed cyptomere structure

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Microwave dispersed quinoa starch aggregates into independent granules.

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Dispersed starch granules were hydrated and gelatinized to form network structure.

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Microwave maintained the crystal form while changed the crystallinity.

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Excessive microwave makes the starch partially gelatinize and formed blocks.

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Moderate microwave treatment can improve the hardness and stickiness of quinoa.

Texture characteristics of quinoa under microwave (MW) irradiation were studied from the perspective of starch gelatinization. MW reduced the light transmittance and increased the hardness and stickiness of quinoa. Microstructure showed that MW dispersed the vesicular structure of starch aggregates into separate starch particles, resulting in the full hydration of starch and water molecules to form denser network structures. The value of peak viscosity and setback decreased in RVA after MW treatment, but the gelatinization temperature remained stable. DSC further proved that moderate MW treatment could reduce the gelatinization enthalpy of starch and made quinoa accessible to gelatinize. However, XRD showed that the crystal structure of starch was preserved, but the crystallinity increased. Finally, low field NMR showed that moderate MW stimulated the full hydration of starch to form denser network structures, while excessive MW treatment made starch partially gelatinize and form rigid structure, resulting in negative texture properties.

Microwave reheating enriches resistant starch in cold-chain cooked rice: A view of structural alterations during digestion

Cold-chain cooked rice is an instant food consumed worldwide. Through inspecting rice structural alterations during digestion, this work discloses how microwave reheating tailors the starch digestibility of cooked rice following cold storage. The cold storage allowed approximately 2% of B-type (not V-type) starch crystallites, more nanoscale and short-range orders, and smaller pores in the rice matrix. These changes retarded the hydrolysis of structural domains (e.g., amorphous regions and short-range orders) during digestion, which increased the content of slowly digestible starch to about 38.16%. Then, microwave reheating partially disrupted the B-type crystallites and nanoscale orders, but unaffected the contents of V-type crystallites and short-range orders. Even with such structural disruptions, the resistant starch content was apparently increased to approximately 30.06%, as the structural domains became less susceptible to the digestion. Additionally, for the rice samples, the percentage of V-type crystallites could be largely increased from ca. 3% to 13%-14% during digestion.

Increasing the pH value during thermal processing suppresses the starch digestion of the resulting starch-protein-lipid complexes

To date, how the pH conditions of thermal processing tailor the structure and digestibility of resulting starch-based complexes remains largely unclear. Here, indica rice starch (IRS), stearic acid (SA), and a whey protein isolate (WPI) were used as materials. Increasing the pH value from 4 to 8 during thermal processing (pasting) mainly suppressed the starch digestion of starch-WPI-SA complexes rather than starch-SA counterparts. The starch-SA complexes showed moderate structural changes as the pH value rose, and there was less rapidly digestible starch (RDS) only at pH 8. For the starch-WPI-SA complexes, an increased pH value allowed larger nonperiodic structures and more V-type starch crystallites, with almost unchanged short-range orders but apparently collapsed networks at pH 8. Such ternary complexes displayed more resistant starch (RS) as the pH value rose. The ternary sample at pH 8 contained ca. 29.87% of the RS fractions.

Increasing agar content improves the sol-gel and mechanical features of starch/agar binary system

Starch/agar systems are highly potential for versatile applications such as packaging and biomedical materials. Here, how combined factors affect the features of a starch/agar binary system were explored. An increase of starch amylose/amylopectin ratio from 0/100 to 50/50 increased the sol-gel transition temperature and gel hardness of the aqueous starch/agar mixture. An increased agar content (mainly from 30% to 70%) allowed increases in both the tensile strength (reaching 50-60 MPa) and elongation at break of the starch/agar binary films. This phenomenon should be related to the strengthened crystalline structure and the weakened hydrogen bonding between starch chains (reflected by infrared spectroscopy). Furthermore, a higher relative humidity (from 30% to 70%) allowed enhanced chain interactions and probably nanoscale molecular order but weakened the crystalline structure, leading to reduced tensile strength and increased elongation at break. This work could facilitate the design of starch/agar binary systems with improved sol-gel and mechanical performance.

Microwave Cooking Enriches the Nanoscale and Short/Long-Range Orders of the Resulting indica Rice Starch Undergoing Storage

The chain reorganization of cooked starch during storage plays an important role in the performance of starchy products such as rice foods. Here, different analytical techniques (such as small-angle X-ray scattering) were used to reveal how microwave cooking influences the chain assembly of cooked indica rice starch undergoing storage for 0, 24, or 48 h. While stored, more short-range double helices, long-range crystallites, and nanoscale orders emerged for the microwave-cooked starch than for its conventionally cooked counterpart. For instance, after storage for 24 h, the microwave-cooked starch contained 46.8% of double helices, while its conventionally cooked counterpart possessed 34.3% of double helices. This could be related to the fact that the microwave field caused high-frequency movements of polar groups such as hydroxyls, which strengthened the interactions between starch chains and water molecules and eventually their assembly into double helices, crystallites, and nanoscale orders. This work provides further insights into the chain reassembly of microwave-cooked starch undergoing storage, which is closely related to the quality attributes of starch-based products.

Polyvinyl alcohol inclusion can optimize the sol-gel, mechanical and hydrophobic features of agar/konjac glucomannan system

The practical features (e.g., sol-gel, mechanical and hydrophobic) of biopolymer systems are crucial for their materials applications. This work reveals how polyvinyl alcohol (PVA) inclusion affects the practical features of agar/konjac glucomannan (KGM) system. From rheological analysis, incorporating PVA (especially 6%) enhanced the chain entanglements of resulted ternary solution (A₇₀K₂₄P₆) with stabilized sol-gel transition point. Such effect not only increased the zero-shear viscosity (ca. 1.5 times that of agar/KGM counterpart) and structural recovery degree of A₇₀K₂₄P₆ solution, but also caused reduced crystallites and simultaneously increased tensile strength, elongation at break and hydrophobicity for A₇₀K₂₄P₆ film from solution dehydration. This ternary film exhibited a tensile strength of ca. 105 MPa, an elongation at break of ca. 20%, and a water contact angle of ca. 97.6°. Additionally, incorporating PVA almost unaffected the morphology of film fracture surface. These results are valuable for the design of agar/KGM systems with improved practical features.

Cold-chain cooked rice with different water contents: Retarded starch digestion by refrigeration

Cold-chain cooked rice is a widely-consumed instant food. While the quality of cooked rice as affected by processing has been widely studied, it remains largely unexplored how concurrent cold-chain conditions (e.g., refrigeration time with specific water contents) tailor the structure and starch digestibility of cooked rice. Here, as shown by combined techniques (e.g., scanning electron microscopy and small angle X-ray scattering), the cold storage (1 to 3 days) of cooked rice at 1.1:1 w/w water-to-rice ratio increased the uniformity of the rice matrix, strengthened the nonperiodic structure, and allowed more B-type starch crystallites and short-range orders. This induced an increase in the slowly digestible starch (SDS) content (from ca. 33.7% to 38.5%) as the refrigeration time rose. In contrast, for cooked rice with 1.5:1 w/w water-to-rice ratio, the cold storage (mainly 1 day) strengthened the matrix uniformity and the nonperiodic structure, and eventually increased the resistant starch (RS) content from ca. 10.3% to 17.7%. The present data could facilitate the design of cold-chain cooked rice with tailored starch digestibility.

Textile Waste Fiber Regeneration via a Green Chemistry Approach: A Molecular Strategy for Sustainable Fashion

Fast fashion, as a continuously growing part of the textile industry, is widely criticized for its excessive resource use and high generation of textiles. To reduce its environmental impacts, numerous efforts are focused on finding sustainable and eco-friendly approaches to textile recycling. However, waste textiles and fibers are still mainly disposed of in landfills or by incineration after their service life and thereby pollute the natural environment, as there is still no effective strategy to separate natural fibers from chemical fibers. Herein, a green chemistry strategy is developed for the separation and regeneration of waste textiles at the molecular level. Cellulose/wool keratin composite fibers and multicomponent fibers are regenerated from waste textiles via a green chemical process. The strategy attempts to reduce the large amount of waste textiles generated by the fast-developing fashion industry and provide a new source of fibers, which can also address the fossil fuel reserve shortages caused by chemical fiber industries and global food shortages caused by natural fiber production.

Effect of chlorogenic acid on the structural properties and digestibility of lotus seed starch during microwave gelatinization

The structural evolution of lotus starch (LS)-chlorogenic acid (CA) complexes was investigated after microwave-heating treatment, to reveal the relationship between the interactions of lotus starch and chlorogenic acid molecules, and the digestive properties of the starch, after microwave gelatinization. During the early stage of microwave gelatinization (65, 70 °C), CA was mainly participating in the rearrangement of starch molecules in a weakly-bound form, and at that stage, the LS-CA complex acted as an inhibitor of digestion, under small intestine conditions, mainly through the release of CA, which inhibited amylase. However, during the late stage of microwave gelatinization (85 °C), many chlorogenic acid molecules entered the hydrophobic helical cavity of the starch, promoting formation of the V-type starch helical structure in the LS-CA complex, which made a major contribution to inhibiting digestion under oral digestion conditions.

Effects of microwave treatments and retrogradation on molecular crystalline structure and in vitro digestibility of debranched mung-bean starches

The objective of this study was to investigate morphology, molecular crystalline structure, and digestibility of debranched mung bean starches with or without microwave treatment and retrogradation at different temperature. The mung bean starch was firstly debranched with pullulanase, and then the debranched starch containing 20% moisture content was treated by microwave irradiation for 3 min with or without further retrograded at +25, +4, or -18 °C for 24 h. All treated starches exhibited the B + V-type crystalline polymorph as determined by the XRD and the ¹³CNMR. The FT-IR results showed that the debranched starches had lower degree of order but higher degree of double helix than those of the native starch. The microwave treatment or further recrystallization of the debranched starch for more 24 h significantly improved crystalline structure of starch granules with higher degree of relative crystallinity, degree of order, and degree of double helices. The resistant starch content of the treated starch was in a range of 39.7-52.8%, significantly higher than that of the native starch (15.6%). As a result, the microwave-assisted debranched starch with further crystallization for 24 h was found to have highly ordered structure of granules, which highly resisted to the enzyme digestion.

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.

Microwave technology: a novel approach to the transformation of natural metabolites

Microwave technology is used throughout the world to generate heat using energy from the microwave range of the electromagnetic spectrum. It is characterized by uniform energy transfer, low energy consumption, and rapid heating which preserves much of the nutritional value in food products. Microwave technology is widely used to process food such as drying, because food and medicinal plants are the same organisms. Microwave technology is also used to process and extract parts of plants for medicinal purposes; however, the special principle of microwave radiation provide energy to reaction for transforming chemical components, creating a variety of compounds through oxidation, hydrolysis, rearrangement, esterification, condensation and other reactions that transform original components into new ones. In this paper, the principles, influencing factors of microwave technology, and the transformation of natural metabolites using microwave technology are reviewed, with an aim to provide a theoretical basis for the further study of microwave technology in the processing of medicinal materials.

Microwave reheating increases the resistant starch content in cooked rice with high water contents

This study explored how microwave reheating (to about 73 °C at different power levels) affects the microstructure and digestion characteristics of cooked rice with different water contents (1.1 and 1.5 times that of rice in weight). Irrespective of water content, mainly the V-type crystallites remained after microwaving reheating, with slight changes in other multi-scale structural features. Only at a relatively high water content (1.5) and with a power level high enough could short-range order be reduced. Such microwave reheating increased the digestion resistance of cooked rice. At a water content of 1.1 times, increasing the microwave power led to a decreased rapid digestible starch (RDS) content and an increased resistant starch (RS) content. With a higher water content (1.5), the enhancement of digestion resistance with higher microwave power was less significant but still, a reduced slowly digestible starch (SDS) content and a higher RS content were observed.

Hydrophobic Interface Starch Nanofibrous Film for Food Packaging: From Bioinspired Design to Self-Cleaning Action

Starch-derived edible food films have great potential as biodegradable food packaging materials because they reduce the overuse of traditional petroleum-based plastic. Herein, we demonstrate a direct method of mass producing a pure starch food packaging film that consisted of starch nanofibers by using a temperature-assisted electrospinning technique without addition of any nonstarch components. To overcome the major issue of ultralow hydrophobicity of starch nanofibrous film (SNF), we used a facile and low-cost solution immersion approach to create a fiber coating of stearic acid (STA) inspired by biological organisms with superhydrophobic properties, such as lotus leaves. Hierarchical flower-like micronanostructures were obtained on SNF by controlled assembly of STA onto the surface of starch nanofibers. Benefiting from the effective formation of STA self-assembled lamella, the multiscale microstructure surface features, low surface energy, and enhancing thermal stability of SNF were obtained and confirmed to result in the variety of its hydrophobicity, which can be also tailored by simple controlling of the solution concentration of STA. Importantly, the STA-self-assembled coated SNF enabled water to roll freely in all directions, which is a crucial factor for self-cleaning. Our novel strategy based on self-assembly can guide development of bioinspired hydrophobic interfaces for starch-based films for edible hydrophobic materials.

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.

Plasticized Starch/Agar Composite Films: Processing, Morphology, Structure, Mechanical Properties and Surface Hydrophilicity

Natural biopolymers, which are renewable, widely available, biodegradable, and biocompatible, have attracted huge interest in the development of biocomposite materials. Herein, formulation–property relationships for starch/agar composite films were investigated. First, rapid visco analysis was used to confirm the conditions needed for their gelation and to prepare filmogenic solutions. All the original crystalline and/or lamellar structures of starch and agar were destroyed, and films with cohesive and compact structures were formed, as shown by SEM, XRD, and SAXS. All the plasticized films were predominantly amorphous, and the polymorphs of the composite films were closer to that of the agar-only film. FTIR results suggest that the incorporation of agar restricted starch chain interaction and rearrangement. The addition of agar to starch increased both tensile strength and elongation at break, but the improvements were insignificant after the agar content was over 50 wt.%. Contact angle results indicate that compared with the other samples, the 4:6 (wt./wt.) starch/agar film was less hydrophilic. Thus, this work shows that agar dominates the structure and properties of starch/agar composites, and the best properties can be obtained with a certain starch/agar ratio. Such composite polysaccharide films with tailored mechanical properties and surface hydrophilicity could be useful in biodegradable packaging and biomedical applications (wound dressing and tissue scaffolding).

Starch-protein interplay varies the multi-scale structures of starch undergoing thermal processing

This work concerns how starch-protein interplay affects the multi-scale structures (e.g., short- and long-range orders, nanoscale structure and morphology) of starch undergoing thermal processing (pasting) involving heating and cooling at high water content. An indica rice starch (IRS) and three proteins (whey protein isolate, WPI; soy protein isolate, SPI; casein, CS) were used. By inspecting rheological profiles of mixed systems before and after adding chemicals, IRS-WPI and IRS-CS showed mainly hydrophobic molecular interaction; and IRS-SPI exhibited hydrophobic, hydrogen bonding and electrostatic interactions. The RVA results revealed that, with starch and proteins as controls, starch-globular protein (WPI or SPI) interplay accelerated the swelling of starch granules (faster viscosity increase at initial pasting stage), and reduced the paste stability during heating (higher breakdown) and during cooling (higher setback); however, the starch-casein interactions resulted in opposed effects. Moreover, starch-protein interactions varied the multi-scale chain reassembly of starch into different structures during cooling. Observed could be fewer short- and long-range starch orders, and larger nonperiod structure (or colloidal clusters) on the nanoscale. On even larger scale to micron, IRS-globular protein molecules generated larger grids (with reduced number) in the gel network, and IRS-casein formed a more continuous gel network with less prominent tunnel-like features.

Reactive extrusion-processed native and phosphated starch-based food packaging films governed by the hierarchical structure

The aim of this research work was to investigate novel tools given by nanotechnology and green chemistry for improving the disadvantages typically associated to the starch-based films: water susceptibility and brittle mechanical behavior. With this in mind, four food packaging film systems were developed from corn starch or corn starch nanocrystals (SNCs), and modified by phosphating under reactive extrusion (REx) conditions using sodium tripolyphosphate (Na₅P₃O₁₀ - TPP) as a crosslinker. The structural, physicochemical, thermal, rheological and mechanical properties, as well as studies associated with the management of carbohydrate polymer-based plastic wastes (biodegradability and compostability) were carried out in this study. The hierarchical structure and the modification of the starch were dependent on the amylose content and degree of substitution (DS), which in turn depended on the hydrogen (H)-bonding interactions. In both cases, a higher molecular ordering of the starch chains in parallel was decisive to obtain the self-assembled thermoplastic starches. Beyond the valuable results obtained and scientifically analyzed, unfortunately none of the manufactured materials achieved to improve their performance compared to the control film (thermoplastic starch - TPS). It was even thought that the phosphated starch-based films could fertilize lettuce (Lactuca sativa) seedlings during their biodegradation, and this was not achieved either. This possibly due to the low content of phosphorus or its poor bioavailability.

Storage temperature and time affect the enzyme resistance starch and glycemic response of cooked noodles

White-salted noodles are prepared, stored and consumed in various ways. However, relationships among cooking and storage conditions on nutritional functionality are not fully understood. The manuscript elucidates the mechanism of formation of resistant starch (RS) leading to slower digestion rate of variously cooked (boiled, steamed, stir-fried, fried and microwave heated) noodles followed by storage under different conditions (-18, 4 and 25 °C for 4, 24 and 48 h). RS content of noodles stored at 25 °C was higher than noodles stored at 4 °C, which was consistent with increases in the degree of crystallinity during storage. We showed that the residual moisture content primarily facilitated the mobility of starch chains and contributed towards the increase in RS associated with the decrease of enzyme susceptivity of noodles after storage. Evidence that supramolecular organization (helical structure and crystallinity) had a more pronounced effect than the macroscopic structure such as compactness or bulk density was also provided.