Different variations in structures of A- and B-type starches subjected to microwave treatment and their relationships with digestibility

Purification and characterization of betacyanin monomers from Hylocereus polyrhizus peel: A comparative study of their antioxidant and antidiabetic activities with mechanistic insights

Betacyanins have garnered escalating research interest for their promising bioactivities. However, substantial challenges in purification and separation have impeded a holistic comprehension of the distinct bioactivities of individual betacyanins and their underlying mechanisms. Herein, betanin and phyllocactin monomers with purity exceeding 95% were successfully obtained from Hylocereus polyrhizus peel using a feasible protocol. These monomers were subsequently employed for comparative bioactivity assessments to uncover underlying mechanisms and illuminate structure-activity relationships. Interestingly, phyllocactin exhibited superior antioxidant activities and 36.1% stronger inhibitory activity on α-glucosidase compared to betanin. Mechanistic studies have revealed that they function as mixed-type inhibitors of α-amylase and competitive inhibitors of α-glucosidase, with interactions predominantly driven by hydrogen bonding. Notably, phyllocactin demonstrated a greater binding affinity with enzymes than betanin, thereby substantiating its heightened inhibitory activity. Overall, our results highlight novel bioactivities of betacyanin monomers and provide profound insights into the intricate interplay between structures and properties.

Effect of microwave-assisted treatment on proximate, techno-functional, thermal, structural, and storage properties of TGN (Cyperus esculentus L.) flour

BACKGROUND

The use of the emerging technique of microwave-assisted roasting on TGN (TGN) flour was investigated. Tiger nuts were subjected to microwave irradiation at 450, 600, and 900 W each at 5, 10, and 15 min, and milled to flour. The flours were analyzed for proximate, bioactive, techno-functional, morphological, thermal, and storage effects on their composition. An untreated sample was the control.

RESULTS

The results revealed that microwave treatment significantly (P < 0.05) elicited various modifications in the proximate composition and techno-functional properties. The treatment improved the bioactive composition of phenolic content together with the antioxidant activity of the flour. Progressive microwave treatment of TGNs resulted in flours with darker colors and reduced pasting parameters. Structural modification of starch granules, protein denaturation, and starch-protein complexes occasioned by microwave treatment were evidenced in the functional group analysis, including morphological agglomeration, increased particle size, and thermal properties. Treatment also enhanced the microbiological qualities of flour after 8 weeks of storage.

CONCLUSION

This study shows that microwave treatment produces excellent physical modifications that lead to improvements in the nutritional, functional, sensory, and color properties, and safety attributes of TGN flour for food application. This is a development that could present opportunities for novel food formulation by the food industry and related industries. © 2024 Society of Chemical Industry.

Comparative sensitivity of A-type and B-type starch crystals to ultrahigh magnetic fields

In this study, maize starch (A-type) and potato starch (B-type) were treated with ultrahigh magnetic fields (UMF) of different intensities (5 T and 15 T) to investigate their sensitivity to UMF by measuring changes in their structure and rheological properties. The results indicate that the crystallinity of A-type starch significantly decreases, reaching a minimum of 20.01 % at 5 T. In contrast, the crystallinity of B-type starch significantly increases, peaking at 21.17 % at 15 T, accompanied by a brighter polarized cross and a more perfect crystal structure. Additionally, B-type starch exhibited a significant increase in double helix content (from 32.67 % to 42.07 %), branching degree (from 1.96 % to 3.84 %), and R1022/995 (from 0.803 to 0.519), compared to A-type starch. B-type starch also showed a greater propensity for cross-linking reactions forming OCOR groups (from 0 % to 6.81 %), and its enthalpy change (∆H) increased substantially (from 19.28 J/g to 31.70 J/g), indicating a marked enhancement in thermal stability. Furthermore, the average hydrodynamic radius (Rh) decreased more for B-type starch, reflecting an increase in gel strength. These findings demonstrate that B-type starch is more sensitive to UMF than A-type starch. This study provides foundational data on the effects of UMF treatment on different crystalline starches, aiming to explore its potential applications in food and industrial fields.

Effect of microwave alone and microwave-assisted modification on the physicochemical properties of starch and its application in food

Native starch has poor stability and usually requires modification to expand its industrial application range. Commonly used methods are physical, chemical, enzymatic and compound modification. Microwave radiation, as a kind of physical method, is promising due to its uniform energy radiation, greenness, safety, non-toxicity. It can meet the demand of consumers for safe food. Microwave-assisted modification with other methods can directly or indirectly affect the structure of starch granules to obtain modified starch with high degree of substitution and low viscosity, and the modification efficiency is greatly improved. This paper reviews the effect of microwave radiation on the physicochemical properties of starch, such as granule morphology, crystallization characteristics, and gelatinization characteristics, as well as the application of microwave radiation in starch modification and starch food processing. It provides theoretical references and suggestions for the research of microwave heating modified starch and the deep processing of starchy foods.

The multi-scale structure changes of γ-ray irradiated potato starch to mitigate pasting/digestion properties

The comprehensive understanding of multi-scale structure of starch and how the structure regulates the pasting/digestion properties remain unclear. This work investigated the effects of γ-ray irradiation with different doses on multi-scale structure and pasting/digestion properties of potato starch. Results indicated that γ-ray at lower doses (<20 kGy) had little effect on micromorphology of starch, increased mainly the amylose content and the thickness of amorphous region while decreased crystallinity, double helix content and lamellar ordering. With the increase of dose, the internal structure of large granules was destroyed, resulting in the depolymerization of starch to form more short-chains and to reduce molecular weight. Meanwhile, amylose content decreased due to the depolymerization of amylose. The enhanced double helix content, crystallinity, lamellar ordering and structural compactness manifested the formation of the thicker and denser starch structure. These structure changes resulted in the decreased viscosity, the increased stability and anti- digestibility of paste.

Effect of structural characteristics of resistant starch prepared by various methods on microbial community and fermentative products

Resistant starch (RS) has been extensively studied because of its beneficial effects on gut microbiota. In this study, four RSs obtained through various preparation processes were utilized for in vitro fermentation, and their structural characteristics before and after fermentation were determined using chromatography, Fourier infrared spectroscopy, and scanning electron microscopy (SEM). It was observed that these RSs can be classified into two categories based on their fermentation and structural features. The autoclaving RS (ARS) and extruding RS (ERS) were classified as Class I Microbiome Community (MC-I), characterized by a higher proportion of butyrate and its producers, including unclassified_g_Megasphaera and Megasphaera elsdenii. While microwaving RS (MRS) and ultrasound RS (URS) belonged to Class II Microbiome Community (MC-II), marked by a higher proportion of acetate and its producer, Bifidobacterium pseudocatenulatum DSM 20438. MC-I had a lower molecular weight, shorter chain length, more chains with degree of polymerization (DP) 36-100, and a more ordered structure than MC-II. Furthermore, SEM observations revealed distinct degradation patterns between MC-I and MC-II, which may be attributed to their surface structural characteristics. These findings imply that the preparation methods employed for RS can determine its multilevel structural characteristics, and consequently influence its physiological properties.

Preparation, structure, and in-vitro hypoglycemic potential of debranched millet starch-fatty acid composite resistant starch

Currently, the preparation methods and basic physicochemical properties of starch-FA complexes have been widely studied; however, no in-depth research on the regulatory mechanism of the digestive properties of debranched starch-unsaturated FA complexes has been conducted. Therefore, six fatty acids with different carbon chains and different degrees of unsaturation were complexed with de-branched millet starch in this research, using the microwave method. Microwave millet starch-linoleic acid complex (MPS-LOA) had the highest resistant starch (RS) content, and the structure and physicochemical properties of MPS-LOA were determined using various molecular techniques. The results indicate that MPS-LOA had a resistant starch (RS) content of 40.35% and the most notable fluorescence. The characteristic UV peaks of MPS-LOA were blue-shifted, and new IR peaks appeared. The crystalline structure changed to V-type crystals, the crystallinity increased, and the molecular weight decreased. The enthalpy and coagulability of MPS-LOA increased, and the swelling force decreased. Additionally, MPS-LOA showed enhanced α-glucosidase and α-amylase inhibition, and in-vitro hydrolysis kinetics analysis of MPS-LOA showed a hydrolysis index of 53.8 and an extended glycemic index (eGI)I of 54.6, indicating a low eGI food suitable for consumption by people with type II diabetes. These results provide a theoretical basis for the preparation of amylopectin- and starch-based foods with an anti-enzyme structure and a low glycemic index (GI).

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Thermal processing remains the key processing technology for food products. However, there are some limitations for thermal processing such as loss of sensory and nutritional quality. Furthermore, nowadays consumers are looking forward for fresh like products which are free from chemical preservatives, yet having longer shelf life. Thus, alternative processing techniques are gaining popularity among food processors to replace conventional thermal processing keeping nutritional quality, sensory attributes and food safety in mind. The alternative processing techniques such as ultrasound, gamma irradiation, high pressure processing and microwave treatment causes several modifications (structural changes, effects on swelling and solubility index, gelatinization behaviour, pasting or rheological properties, retrogradation and cooking time) in physicochemical and functional properties of pulse starches which offers several advantages from commercial point of view. This review aims to summarize the effect of different alternative processing techniques on the structure, solubility, gelatinization, retrogradation and pasting properties of various pulse starches.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-022-05557-3.

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.

Preparation, multi-scale structures, and functionalities of acetylated starch: An updated review

Acetylated starch has been widely used as food additives. However, there was limited information available regarding the impact of acetylation on starch structure and functionalities, as well as the advanced acetylation technologies. This review aimed to summarize current methods for starch acetylation and discuss the structure and functionalities of acetylated starch. Innovative techniques, such as milling, microwave, pulsed electric fields, ultrasonic, and extrusion, could be employed for environmental-friendly synthesis of acetylated starch. Acetylation led to the degradation of starch structures and weakening of the interactions between starch molecules, resulting in the disorganization of starch multi-scale ordered structure. The introduction of acetyl groups retarded the self-reassembly behavior of starch, leading to increased solubility, clarity, and softness of starch-based hydrogels. Moreover, the acetyl groups improved water/oil absorption capacity, emulsifiability, film-forming properties, and colonic fermentability of starch, while reduced the susceptibility of starch molecules to enzymes. Importantly, starch functionalities were largely influenced by the decoration of acetyl groups on starch molecules, while the impact of multi-scale ordered structures on starch physicochemical properties was relatively minor. These findings will aid in the design of structured acetylated starch with desirable functionalities.

Insights into the changes of structure and digestibility of microwave and heat moisture treated quinoa starch

In this study, quinoa starch was subjected to microwave and heat moisture treatment (MHT) with various moisture content (15 %, 25 %, 35 %) and microwave power (4.8, 9.6, 14.4 W/g), and its structure and digestibility were investigated. SEM and particle size analysis indicated that MHT caused the agglomeration of starch granules and increased the particle size. Moreover, MHT increased the short-range order structure and relative crystallinity, except for MHT with moisture content (35 %). DSC results demonstrated that the gelatinization temperature and gelatinization enthalpy had a slight improvement after MHT. Moreover, MHT increased the amylose content to some extent. It was worth noting that the digestibility of quinoa starch significantly decreased. After MHT, a part of rapidly digestible starch (RDS) was converted into slowly digestible starch (SDS) or resistant starch (RS). Particularly, when moisture content was 25 %, the starch had a highest SDS + RS content. Thus, this study provided a potential approach using MHT to modulate the digestibility of starch.

Changes on Techno-Functional, Thermal, Rheological, and Microstructural Properties of Tef Flours Induced by Microwave Radiation-Development of New Improved Gluten-Free Ingredients

Tef [Eragrostis tef (Zucc.) Trotter] flour is a gluten-free cereal rich in fiber, minerals, vitamins, and antioxidants, which offers a promising alternative for new food development. This study investigated the effect of microwave radiation (MW) on the techno-functional, thermal, rheological and microstructural properties of tef flours. White and brown tef grains were milled and microwaved at different moisture contents (MC) (15%, 20% and 25%) for a total irradiation time of 480 s. The morphological structure of tef flours was affected by MW treatment, and its particle size and hydration properties increased after the treatment. Lower peak, breakdown, and setback viscosities, up to 45%, 96%, and 67% below those of the control (untreated) samples, and higher pasting temperature, up to 8 °C in the 25% MC samples, were observed. From FTIR analysis a disruption of short-range molecular order was concluded, while DSC confirmed an increased stability of starch crystallites. Rheological analysis of the gels made from the treated samples revealed that MW had a structuring and stabilizing effect on all samples, leading to higher viscoelastic moduli, G' and G″, and the maximum stress the gels withstood before breaking their structure, τ_max. The MC of the flours during the MWT drove the modification of the techno-functional properties of the tef flours and the gel rheological and thermal characteristics. These results suggest that MW-treated tef flours are potential ingredients for improving the technological, nutritional and sensory quality of food products.

Influences of high hydrostatic pressure on structures and properties of mung bean starch and quality of cationic starch

It is difficult to improve the quality of chemical-modified starch by traditional technology. Hence, in this study, mung bean starch with poor chemical activity was used as raw material, the native starch was treated and the cationic starch was prepared under high hydrostatic pressure (HHP) at 500 MPa and 40 °C. By studying the changes in the structure and properties of native starch after HHP treatment, the influence mechanism of HHP on improving the quality of cationic starch was analyzed. Results showed high pressure could make water and etherifying agent enter the starch granules through pores, and HHP made the structure of starch undergone three stages similar to mechanochemical effect. After HHP treated for 5 and 20 min, the degree of substitution, reaction efficiency and other qualities of cationic starch increased remarkably. Hence, proper HHP treatment could help to improve the chemical activity of starch and quality of cationic starch.

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.

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.

Physical, Chemical and Biochemical Modification Approaches of Potato (Peel) Constituents for Bio-Based Food Packaging Concepts: A Review

Potatoes are grown in large quantities and are mainly used as food or animal feed. Potato processing generates a large amount of side streams, which are currently low value by-products of the potato processing industry. The utilization of the potato peel side stream and other potato residues is also becoming increasingly important from a sustainability point of view. Individual constituents of potato peel or complete potato tubers can for instance be used for application in other products such as bio-based food packaging. Prior using constituents for specific applications, their properties and characteristics need to be known and understood. This article extensively reviews the scientific literature about physical, chemical, and biochemical modification of potato constituents. Besides short explanations about the modification techniques, extensive summaries of the results from scientific articles are outlined focusing on the main constituents of potatoes, namely potato starch and potato protein. The effects of the different modification techniques are qualitatively interpreted in tables to obtain a condensed overview about the influence of different modification techniques on the potato constituents. Overall, this article provides an up-to-date and comprehensive overview of the possibilities and implications of modifying potato components for potential further valorization in, e.g., bio-based food packaging.

Effects of dual modification of lysine and microwave on corn starch: In vitro digestibility and physicochemical properties

The effects of lysine addition and microwave treatment (MC) on the digestibility, physicochemical properties and structure of corn starch were investigated. Among all uncooked samples, unmodified corn starch (CS), microwave modified corn starch (MC-CS) and corn starch mixed with lysine (CS-Lys) contained 15.09 %, 14.82 % and 18.86 % slowly digestible starch (SDS), while up to 30.28 % in microwave-lysine modified corn starch (MC-Lys). In contrast to CS, the peak viscosity, breakdown viscosity, setback viscosity and gel enthalpy of MC-Lys were decreased, while the relative crystallinity was increased. Scanning electron microscopy observation showed that corn starch aggregated with each other and was coated by lysine after MC, the particle size distribution range became wider, and the specific surface area decreased. The results showed that the interaction of starch with lysine in the microwave field increased the ordered and aggregated structure of corn starch, resulting in a significant change in the physicochemical properties and digestibility of corn starch. MC-Lys can be added to foods as a nutritional fortification to meet the needs of specific populations for lysine and low carbohydrate.

Formation of Intermediate Amylose Rice Starch-Lipid Complex Assisted by Ultrasonication

Due to the potential reduction in starch availability, as well as the production of the distinct physico-chemical characteristics of starch in order to improve health benefits, the formation of starch–lipid complexes has attracted significant attention for improving the quantity of resistant starch (RS) content in starchy-based foods. The purpose of this research was to apply ultrasonication to produce intermediate amylose rice (Oryza sativa L.) cv. Noui Khuea (NK) starch–fatty acid (FA) complexes. The effects of ultrasonically synthesized conditions (ultrasonic time, ultrasonic amplitude, FA chain length) on the complexing index (CI) and in vitro digestibility of the starch–FA complex were highlighted. The optimum conditions were 7.5% butyric acid with 20% amplitude for 30 min, as indicated by a high CI and RS contents. The ultrasonically treated starch–butyric complex had the highest RS content of 80.78% with a V-type XRD pattern and an additional FTIR peak at 1709 cm⁻¹. The increase in the water/oil absorption capacity and swelling index were observed in the starch–lipid complex. The pasting viscosity and pasting/melting temperatures were lower than those of native starch, despite the fact that it had a distinct morphological structure with a high proportion of flaky and grooved forms. The complexes were capable of binding bile acid, scavenging the DPPH radical, and stimulating the bifidobacterial proliferation better than native starch, which differed depending on the FA inclusion. Therefore, developing a rice starch–lipid complex can be achieved via ultrasonication.

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.

Changes in structures and digestibility of amylose-oleic acid complexes following microwave heat-moisture treatment

Amylose-oleic acid complexes (AOA) were exposed to microwave heat-moisture treatment (M-HMT) with different moisture content (MC), and the variations in structures and digestibility were investigated. M-HMT caused the dissociation of helical structures and destruction of short-range molecular order of AOA. Meanwhile, the molecules of amylose and oleic acid rearranged and more amylose-oleic acid complexes were formed during M-HMT, the complexing index of AOA was increased from 25.41 % to 41.20 % when treating at 35 % MC. Moreover, the relative content of single helix increased with increasing MC, resulting in higher V-type relative crystallinity. With ≥30 % MC, the treated complexes showed greater thermostability than that of original AOA. The treatment increased the enzymatic digestibility of AOA, and sample treated with 35 % MC had the highest resistant starch content of 82.33 %, which was 17.96 % higher than that of native AOA. The improved enzyme resistance should be correlated to increased molecular interplay and formation of amylose-oleic acid complexes.

Impact of microwave irradiation on chemically modified talipot starches: A characterization study on heterogeneous dual modifications

In this study, the effect of chemical modifications such as oxidation, esterification and crosslinking was investigated alone and in combination with microwave irradiation on a non-conventional starch with 76% starch yield acquired from the trunk of matured talipot palm. The single- and dual-modifications imparted significant changes in the morphological, crystalline, pasting and rheological properties and digestibility of talipot starch. Characteristic peaks were observed in single- and dual-oxidized, esterified and crosslinked starches indicating their respective functional groups. All modifications significantly decreased (p ≤ 0.05) the relative crystallinity (RC) of talipot starches except for crosslinking, and the least RC (11.33%) was observed in microwave irradiated esterified starch. Microwave irradiation prior to chemical modifications showed a significant impact in the swelling and solubility of talipot starches. The decreased setback viscosity and increased light transmittance in single- and dual-microwave irradiated talipot starches showed their lowered retrogradation tendency, suitable for frozen foods. The resistant starch (RS) content was majorly improved in all heterogeneously dual modified talipot starches by incorporating more functional groups owed to structural and crystalline destruction in starch granules upon microwave irradiation. The highest RS content (45.02%) was observed in microwave irradiated esterified uncooked talipot starch.

Comparison of physicochemical properties and digestibility of sweet potato starch after two modifications of microwave alone and microwave-assisted L-malic acid

The effects of microwave alone (MA) and microwave-assisted L-malic acid (MLA) on the physicochemical properties, structural and digestibility of sweet potato starch were investigated. The results showed that the swelling power, lightness (L^⁎) and whiteness index (WI), gelatinization enthalpy of starch decreased by MA and MLA treatment. The starch treated by MLA showed a new characteristic absorption peak at near 1735 cm^-1 in the measurement of FT-IR, while the starch treated with MA showed no new characteristic peak. The relative crystallinity of starch modified by MSE and MA decreased, but it still retained A-type crystal structure. Scanning electron microscopy showed that the surface destruction of MSE-modified starch was greater than that of starch modified by MA. MLA increased the content of resistant starch (RS), while MA reduced the content of resistant starch (RS). The relative crystallinity and gelatinization enthalpy of continuous 60 s treatment were lower than those of discontinuous 60 s treatment. These results indicated that MLA had a greater effect on the physicochemical properties, structural and digestibility of starch than MA. Starch modified by MLA can be added to foods as a low-carbohydrate ingredient, and the starch treated by MA is suitable for foods with low swelling, such as noodles.

Optimization of Microwave Pre-Cooked Conditions for Gelatinization of Adzuki Bean

Pre-cooked adzuki beans (Vigna angularis), which looks like dried adzuki bean, is easily cooked and preserved. This study aimed to optimize the microwave pre-cooked conditions on adzuki beans by applying the response surface methodology. The results showed that soaking time has a significant effect on the gelatinization degree of adzuki beans according to microwave time. The most suitable gelatinization and the sensory scores were obtained with a soaking time of 7.8 h, a microwave power of 830 W, and microwave time of 92 s. The pre-cooked treatment had no significant effect (p > 0.05) on the protein, free amino acid, fat and starch content of adzuki bean products. The results of SEM and polarized light microscopy showed that the surface and center of starch were damaged after microwave treatment. XRD showed that microwave pre-cooking did not change the crystal structure of starch and maintained the original order of type A structure while reducing the relative starch crystallinity. FT-IR showed that the pre-cooked treatment did not produce new structure in adzuki bean starch, but the ratio of 1047/1022 cm^-1 was slightly decreased, indicating that the starch crystallization area decreased relative to the amorphous area and the relative crystallinity decreased. The results of FTIR were consistent with X-ray diffraction results. Therefore, microwaves improved the gelatinization of adzuki beans and made the pre-cooked adzuki beans more suitable.

Retaining a large amount of resistant starch in cooked potato through microwave heating after freeze-drying

Resistant starch (RS) is beneficial for humans, especially for the diabetes. Raw potato had a great deal of RS, while most of which become digestible after gelatinization. Thus, few RS will be retained in potatoes after regular cooking. To preserve RS in cooked potatoes as much as possible, microwave heating before (MFD) and after freeze-drying (FDM) were conducted with three different potatoes. After MFD, the RS content in potatoes was lower than 7% and the RDS content was higher than 45% for three potatoes. However, RS in potatoes treated with FDM was still as high as 40%, similar to that in the raw potatoes. Meantime, FDM caused less browning, produced a certain level of pyrazines, benzeneacetaldehyde and other flavor compounds, endowing cooked potatoes special baked flavor. Freeze-drying before microwave heating is a valuable way to reserve RS in cooked potatoes, which could also be used to reserve high RS content in crisp, chips, and other processed potatoes.

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Freeze-drying before microwave heating cause subtle effects on starch properties.

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Cooked potatoes by microwave heating after freeze-drying reserve rich RS.

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Microwave heating after freeze-drying caused less browning.

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Cooked potatoes by microwave heating after freeze-drying had special baking flavor.

Methods for characterizing the structure of starch in relation to its applications: a comprehensive review

Starch is a major part of the human diet and an important material for industrial utilization. The structure of starch granules is the subject of intensive research because it determines functionality, and hence suitability for specific applications. Starch granules are made up of a hierarchy of complex structural elements, from lamellae and amorphous regions to blocklets, growth rings and granules, which increase in scale from nanometers to microns. The complexity of these native structures changes with the processing of starch-rich ingredients into foods and other products. This review aims to provide a comprehensive review of analytical methods developed to characterize structure of starch granules, and their applications in analyzing the changes in starch structure as a result of processing, with particular consideration of the poorly understood short-range ordered structures in amorphous regions of granules.

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.

Understanding the aggregation structure, digestive and rheological properties of corn, potato, and pea starches modified by ultrasonic frequency

Corn starch (CS), potato starch (PtS), and pea starch (PS) were modified by ultrasonic frequency (codes as UFCS, UFPtS and UFPS), and changes in aggregation structure, digestibility and rheology were investigated. For UFCS, the apparent amylose content and gelatinization enthalpy (∆H) decreased, while the R1047/1022 values and relative crystallinity (RC) increased under lower ultrasonic frequencies (20 kHz and 25 kHz). For UFPtS, the apparent amylose content, R1047/1022 values and RC increased, while the ∆H decreased under a higher ultrasonic frequency (28 kHz). For UFPS, the apparent amylose content, R1047/1022 values, RC, ∆H decreased at 20 kHz, 25 kHz and 28 kHz. Cracks were observed on the surface of UFCS, UFPtS and UFPS. These aggregation structure changes increased the resistant starch content to 31.11% (20 kHz) and 26.45% (25 kHz) for UFCS and to 39.68% (28 kHz) for UFPtS, but decreased the resistant starch content to 18.46% (28 kHz) for UFPS. Consistency coefficient, storage modulus, and loss modulus of UFCS, UFPtS and UFPS increased, while the flow behavior index and damping factor decreased. Results indicated that CS, PtS and PS had diverse digestion and rheology behaviors after ultrasonic frequency modification, which fulfilled different demands in starch-based products.

Structural changes of A-, B- and C-type starches of corn, potato and pea as influenced by sonication temperature and their relationships with digestibility

The effect of sonication temperature on the structures and digestion behaviour of corn starch (CS, A-type), potato starch (PtS, B-type), and pea starch (PS, C-type) was investigated. For CS, sonication temperature resulted in a rough surface, decreased apparent amylose content, gelatinization enthalpy and gelatinization degree, increased short-range orders, long-range orders, retrogradation degree and resistant starch content. For PtS, sonication temperature led to a coarser surface with scratches, increased apparent amylose content and gelatinization degree, decreased short-range orders, long-range orders, gelatinization enthalpy, retrogradation degree, and resistant starch content. For PS, sonication temperature showed partial disintegration on surface, increased gelatinization degree, decreased apparent amylose content, short-range orders, long-range orders, gelatinization enthalpy, retrogradation degree and resistant starch content. This study suggested that starch digestion features could be controlled by the crystalline pattern of starch used and the extent of sonication temperature, and thus were of value for rational control of starch digestion features.

Atmospheric pressure plasma jet pretreatment to facilitate cassava starch modification with octenyl succinic anhydride

Cassava starch (CS) was pretreated with atmospheric pressure plasma jet (APPJ), followed by esterification with octenyl succinic anhydride (OSA). This study was the first report investigating the effect of APPJ on CS modification with OSA. Results showed that APPJ pretreatment could change the morphological characteristics and crystallinity of CS. Consequently, the degree of substitution and reaction efficiency significantly improved compared with the unpretreated CS (P < 0.05). In Confocal laser scanning microscopy, the fluorescence intensity of OSA-modified CS pretreated with APPJ for 10 min and 15 min was higher than those pretreated with APPJ for 1, 3, and 5 min. The onset temperature and enthalpy (ΔH) of native starch decreased after APPJ pretreatment and further decreased by OSA modification. APPJ-OSA-CS also showed better emulsion stability and emulsion activity. This study demonstrated that APPJ could be used as a novel approach to facilitate starch modification with OSA.

Effects of different moisture contents on the structure and properties of corn starch during extrusion

Herein, corn starch samples with different moisture contents (native corn starch, 30, 35, 40, 45, and 50%) were prepared by twin-screw extrusion, and the structural and physical properties were analyzed and correlated. Scanning electron microscopy observed the morphology, attenuated total reflection-Fourier transform infrared spectroscopy investigated the double helix structure, X-ray diffraction analyzed the crystal region, ion chromatography observed the chain length distribution, and rapid viscosity analyzer measured the viscosity of corn starch samples. We found that the corn starch crystallinity, degree of order, and double helix degree decreased with increasing moisture content. The moisture content has a crucial role in the peak viscosity, breakdown, final viscosity, and setback in pasting property experiments. With the increase in moisture content, the longer chain was transformed into a shorter chain, and the dispersion of molecular weight distribution continuously increased. This study provides a theoretical basis for the production of extruded corn starch.

Infrared heating under optimized conditions enhanced the pasting and swelling behaviour of cowpea starch

Native starches are not suitable for industrial use and must be modified for improved functionality. In this study, the effect of moisture preconditioning and infrared heating time on physicochemical properties of cowpea starch was investigated using a two-factor central composite rotatable design. Factors (moisture levels:10-40 g/100 g starch and infrared heating time:10-60 min) with their corresponding α mid-point values resulted in 13 experimental runs. Selected functional and pasting properties were determined as response variables. Starch samples produced under optimized conditions were compared with corn starch and their physicochemical properties determined. Except for pasting temperature, cowpea starch prepared using the optimal conditions (moisture: 46.21 g/100 g starch, dry basis and heating time of 32.88 min) had higher functional and pasting properties compared with the native cowpea starch. Infrared heating significantly reduced the gelatinization temperatures of cowpea starch but did not significantly change that of the corn starch. The crystallinity and double-helical order structure of moisture conditioned cowpea starch also reduced after modification. Cowpea starch showed a bigger granule size, higher swelling power but lower water absorption capacities and pasting properties compared with the control. The infrared heating process is a novel and promising modification method for improving the swelling properties of starch.

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.

Structural variations of rice starch affected by constant power microwave treatment

Although lots of work has reported the structural variations of starch in microwave treatment, most of them are detected in the environment with non-constant microwave power and inhomogeneous heating, and the results are always in poor repeatability. In this study, the equipment with constant microwave power (CPM) and homogeneous heating was designed. And the phase transition of multi-scale structure of rice starch (30% moisture content) caused by CPM treatments with two heating modes, namely rapid microwave heating (RWH) and slow microwave heating (SWH) were investigated systematically. SEM results showed that the surface of starch granules after CPM treatment were rough and broken, and the damage caused by RWH was more distinct than that by SWH. SAXS, XRD and ¹³C NMR results revealed that the CPM treatment decreased the degree of crystallinity and content of double helices of starch. Moreover, the influence of RWH on the variation of starch granules was greater than that of SWH, which can be attributed to the intensive friction and collision as well as the rapid evaporation of water in RWH treatment. Specifically, it exhibited greater destruction on the linkage of starch and the internal crystalline region in RWH treatment than SWH treatment, thereby resulting in more obvious damages on the lamellar and morphological structure of rice starch. In conclusion, CPM equipment has improved the problems of uneven heating and poor experimental repeatability. After CPM treated starch, the molecular structure of starch was destroyed, which provides a useful method to modify properties of starch.

Insights into the structure and conformation of potato resistant starch (type 2) using asymmetrical flow field-flow fractionation coupled with multiple detectors

Insight into the structure and conformation characteristics of starch that influence its enzyme susceptibility is import for its potential application. In this study, the capacity of asymmetrical flow field-flow fractionation (AF4) coupled online with multi-angle light scatting (MALS) and differential refractive index (dRI) detectors (AF4-MALS-dRI) for monitoring of change in structure and conformation of potato starch during enzymatic hydrolysis was evaluated. The dissolution behavior of potato resistant starch (type 2) (PRS) was investigated. The effect of incubation time and amyloglucosidase concentration on the structure and conformation of potato starch was studied. The apparent density and the ratio of R_g (radius of gyration) to R_h (hydrodynamic radius) obtained from AF4-MALS-dRI were proven to be important parameters as they offer an insight into conformation of PRS at molecular level. Results suggested that gelatinization process made potato amylose molecules have a loose and random coil conformation which could contribute to an acceleration of enzymatic hydrolysis of potato starch. Furthermore, an intermediate with an elongated branched conformation was found between amylose and amylopectin populations, which may play a role in digestion property of potato starch. The results demonstrated that AF4-MALS-dRI is a powerful tool for better understanding of conformation of PRS.

Insights into the multiscale structure and pasting properties of ball-milled waxy maize and waxy rice starches

The effects of ball-milling on the pasting properties of waxy maize starch (WMS) and waxy rice starch (WRS) were investigated from a multiscale structural view. The results confirmed that ball-milling significantly destroyed the structures of the two waxy starches (especially WMS). Specifically, ball-milling led to obvious grooves on the surface of starch granules, a decrease in crystallinity and the degree of short-range order, and a reduction in double-helix components. Meanwhile, small-angle X-ray scattering results indicated that the semicrystalline lamellae of starch were disrupted after ball-milling. Ball-milling decreased the pasting temperatures. Furthermore, ball-milled starches exhibited lower peak and breakdown viscosity and weakened tendency to retrogradation. These results implied that ball-milling induced structural changes in starch that significantly affected its pasting properties. Hence, ball-milled starch may serve as food ingredients with low pasting temperature and paste viscosity as well as high paste stability under heating/cooling and shearing.