Effect of short microwave heating time on physicochemical and functional properties of Bambara groundnut starch

Effect of microwave treatment on the structural and physicochemical properties of amylose partially removed sorghum starch

This study aimed to probe the influence of amylose in starch granules on starch modification. Part of the amylose from sorghum starch was removed through warm water leaching, and the samples were then microwaved. The effects of treatments on starch structure, physicochemical properties, and digestibility were researched. Compared to sorghum starch without partial amylose removal, warm water leaching of amylose resulted in deeper concavity of sorghum starch granules and lower crystallinity, short-range ordering, setback and breakdown values, which disrupted the structure and thus rendered the starch granules more susceptible to microwave radiation, amplifying the advantages of microwave-modified starch. In addition, the ordered arrangement of amylose and amylopectin structures within the microwave-treated sorghum starch with pre-removed amylose were more readily disrupted, allowing enzymes to pass through more readily, thus increasing the fast-digestible starch content and digestibility of the starch. In summary, partial amylose removal can be used as a pretreatment method for modifying and expanding starch utilization in food and non-food industries while providing a new idea for developing baked foods.

Yield, physicochemical properties and in vitro digestibility of starch isolated from defatted meal made from microwaved tigernut (Cyperus esculentus L.) tubers

In this work, the effects of microwave treatment (MDT) of tigernut tubers at 540 W for 140, 180, 220, 240 s on the yield, physicochemical properties and in vitro digestibility of tigernut starch (TS) were firstly investigated. MDT significantly reduced the crystallinity and double helix structures of the starch, without altering its native A-type crystal structure. After microwaving for 140 s and 180 s, the extraction yield of TS was significantly increased from 14.92 % to 16.68 %, and a dense gel network structure was found by rheological analysis. In vitro digestion results indicated that the microwaved TS contained more content of rapidly digestible starch (RDS, 76.10 %-80.74 %) but lower slowly digestible starch (SDS, 2.85 %-5.78 %) and resistant starch (RS, 14.94 %-18.12 %); in other words, microwaving increased the in vitro digestibility of TS. This work elucidated the essential features of the response of tigernut starch to microwave treatment, and provided a basic understand of the digestibility of tigernut starch under microwave treatment, making it more suitable for industrial applications.

Influence of the induced Na+/Cl- ionic polarization effects on multi-scale structures of maize starch during radio frequency heating

Structural modification/unfolding of starch molecules can be improved by radio frequency (RF) treatment. This necessitates a better understanding of its action mechanism through rapid heating and dipolar/ionic molecular vibration effects. Native maize starch (NS) was subjected to RF heating in a NaCl solution to five target temperatures, and its effect on structural modifications was evaluated. Results showed that the conductivity, particle size distribution and zeta potential of RF heated starch increased with increasing temperature. RF energy had a significant effect on the vibration intensity of other skeleton modes. No new chemical bonds/groups were formed in the starch even though there was the effect of sodium/chloride ions with the added vibration intensity of the ions and the dipolar rotation movements resulted in changes in the disordered and/or ordered structures. The RF treatment at 70 °C had the highest energy (10.4 kJ) of inter-strand hydrogen bond, crystallinity (36.6 %) and trough viscosity (2480 cp), but had the lowest crystallite dimension (13.7 nm), full width at half maximum (14.4) of peak at 480 cm-1, and breakdown (534 cp) and setback (784 cp) viscosities based on X-ray diffraction, Fourier transform infrared, and Raman and rapid viscos analyzer observations.

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.

Enhancing enzymatic resistance of starch through strategic application of food physical processing technologies

The demand for clean-label starch, perceived as environmentally friendly in terms of production and less hazardous to health, has driven the advancement of food physical processing technologies aimed at modifying starch. One of the key objectives of these modifications has been to reduce the glycaemic potency and increase resistant starch content of starch, as these properties have the potential to positively impact metabolic health. This review provides a comprehensive overview of recent updates in typical physical processing techniques, including annealing, heat-moisture, microwave and ultrasonication, and a brief discussion of several promising recent-developed methods. The focus is on evaluating the molecular, supramolecular and microstructural changes resulting from these modifications and identifying targeted structures that can foster enzyme-digestion resistance in native starch and its forms relevant to food applications. After a comprehensive search and assessment, the current physical modifications have not consistently improved starch enzymatic resistance. The opportunities for enhancing the effectiveness of modifications lie in (1) identifying modification conditions that avoid the intensive disruption of the granular and supramolecular structure of starch and (2) exploring novel strategies that incorporate multi-type modifications.

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.

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.

Enhancing the nonlinear rheological property and digestibility of mung bean flour gels using controlled microwave treatments: Effect of starch debranching and protein denaturation

In this study, we examined the possibility of using industrial microwave processing to enhance the gelling properties and reduce the starch digestibility of mung bean flour (MBF). MBF (12.6 % moisture) was microwaved at a power of 6 W/g to different final temperatures (100-130 °C), and then its structural and functional properties were characterized. The microwave treatment had little impact on the crystalline structure or amylose content of the starch, but it roughened the starch granule surfaces and decreased the short-range ordered structure and degree of branching. In addition, the extent of mung bean protein denaturation caused by the microwave treatment depended on the final temperature. Slightly denaturing the proteins (100 °C) did not affect the nature of the gels (protein phase dispersed in a starch phase) but the gel network became more compact. Moderately denaturing the proteins (110-120 °C) led to more compact and homogeneous starch-protein double network gels. Excessive protein denaturation (130 °C) caused the gel structure to become more heterogeneous. As a result, the facilitated tangles between starch chains by more linear starch molecules after debranching, and the protein network produced by moderate protein denaturation led to the formation of stronger gel and the improvement of plasticity during large deformation (large amplitude oscillatory shear-LAOS). Starch recrystallization, lipid complexion, and protein network retard starch digestion in the MBF gels. In conclusion, an industrial microwave treatment improved the gelling and digestive properties of MBF, and Lissajous curve has good adaptability in characterizing the viscoelasticity of gels under large deformations.

Formation, influencing factors, and applications of internal channels in starch: A review

Starch, a natural polymer, has a complex internal structure. Some starches, such as corn and wheat starches, have well-developed surface pores and internal channels. These channel structures are considered crucial in connecting surface stomata and internal cavities and have adequate space for loading guest molecules. After processing or modification, the starch-containing channel structures can be used for food and drug encapsulation and delivery. This article reviews the formation and determination of starch internal channels, and the influence of different factors (such as starch species and processing conditions) on the channel structure. It also discusses relevant starch preparation methods (physical, chemical, enzymatic, and synergistic), and the encapsulation effect of starch containing internal channels on different substances. In addition, the role of internal channels in regulating the starch digestion rate and other aspects is also discussed here. This review highlights the significant multifunctional applications of starch with a channel structure.

Effect of microwave followed by cooling on structural and digestive properties of pinhão starch

To increase its resistant content, native pinhão starch was modified using a microwave (300 W, 90 s) and subsequently cooled at 4 °C for 4, 8, 16, 24, and 72 h. The results demonstrated that all starches exhibited a crystalline structure of type C, with decreased crystallinity after modification. In the modified samples, the ratio of peaks 1047/1022 cm-1 and 995/1022 cm-1, as identified by FTIR, indicated a reduction in the crystalline region and damage to the double helix structure of starch granules. DSC analysis revealed that modified starches had lower gelatinization temperature range values due to the presence of more homogeneous crystals. Rheological analyses showed that starch suspensions obtained exhibited pseudoplastic fluid behavior and gel-like viscoelastic structure formation, with higher storage moduli in samples with longer cooling times. The microwave-modified starch, cooled for 72 h, exhibited higher digestion resistance, resulting in a 43.6 % increase in resistant starch content and a 26.1 % decrease in rapidly digestible starch compared to native starch. The results highlight that the modification of native pinhão starch using a microwave, followed by cooling at 4 °C for 72 h, presents a promising method for increasing the resistant starch content.

High-pressure pasting performance and multilevel structures of short-term microwave-treated high-amylose maize starch

Microwave treatment is an environmentally friendly method for modification of high-amylose maize starch (HAMS). Here, the effects of short-time (≤120 s) microwave treatment on the structure and pasting of two types of HAMSs, Gelose 50 (HAMSI) and Gelose 80 (HAMSII), with apparent amylose content (AAC) of 45 % and 58 %, respectively, was studied using a multiscale approach including X-ray scattering, surface structures, particle size distribution, molecular size distributions and high temperature/pressure Rapid Visco Analysis (RVA)-4800 pasting. As compared to starch with no amylose (waxy maize starch, WMS) and 25 % amylose content (normal maize starch, NMS), HAMSI underwent similar structural and pasting changes as WMS and NMS upon microwave treatment, and it might primarily be attributed to the amylopectin fraction that was affected by cleavage of the connector chains between double helices and backbone chains, which decreased the crystallinity and thickness of the crystalline lamellae. However, the multi-scale structure of HAMSII was almost unaffected by this treatment. The pasting properties of fully gelatinized HAMSI starch showed a decrease in RVA-4800 peak and final viscosities after microwave treatment. In contrast, for HAMSII starch, the microwave treatment led to an increase in these viscosities. The combined results highlight the influence of varying AAC on the effects of microwave-mediated modification, leading to diverse alterations in the structure and functionality of starches.

Flavor-food ingredient interactions in fortified or reformulated novel food: Binding behaviors, manipulation strategies, sensory impacts, and future trends in delicious and healthy food design

With consumers gaining prominent awareness of health and well-being, a diverse range of fortified or reformulated novel food is developed to achieve personalized or tailored nutrition using protein, carbohydrates, or fat as building blocks. Flavor property is a critical factor in the acceptability and marketability of fortified or reformulated food. Major food ingredients are able to interact with flavor compounds, leading to a significant change in flavor release from the food matrix and, ultimately, altering flavor perception. Although many efforts have been made to elucidate how food matrix components change flavor binding capacities, the influences on flavor perception and their implications for the innovation of fortified or reformulated novel food have not been systematically summarized up to now. Thus, this review provides detailed knowledge about the binding behaviors of flavors to major food ingredients, as well as their influences on flavor retention, release, and perception. Practical approaches for manipulating these interactions and the resulting flavor quality are also reviewed, from the scope of their intrinsic and extrinsic influencing factors with technologies available, which is helpful for future food innovation. Evaluation of food-ingredient interactions using real food matrices while considering multisensory flavor perception is also prospected, to well motivate food industries to investigate new strategies for tasteful and healthy food design in response to consumers' unwillingness to compromise on flavor for health.

Optimisation of the techno-functional and thermal properties of heat moisture treated Bambara groundnut starch using response surface methodology

This work optimised the techno-functional and thermal properties of heat moisture treated Bambara groundnut starch (BGS). A central composite rotatable design (Design-Expert software v8.0.1.0) comprising two independent factors of temperature and time was used. Extracted BGS were subjected to heat-moisture treatment (HMT) at 80-120 °C for 30-90 min at different moisture levels of 15% (HMT 15-BGS), 25% (HMT 25-BGS) and 35% (HMT 35-BGS). The optimum HMT conditions for BGS were found to be 80 °C for 30 min (HMT 15), 105.74 °C for 30 min (HMT 25), and 113.16 °C for 30 min (HMT 35). The desirability values of the obtained optimum conditions were 0.63 (HMT 15) and 1.00 (HMT 25 and 35). In HMT 35-BGS, water absorption capacity was significantly affected by the quadratic effect of temperature and time. In contrast, solubility was significantly affected by the linear effect of time and the quadratic effect of temperature. Temperature and treatment time had no significant effect (p ≥ 0.05) on the differential scanning calorimetry thermal properties of HMT 15, 25 and 35-BGS. Scanning electron micrographs of optimised BGS showed round and oval-shaped starch granules ranging from 4.2 to 4.7 mm (width) and 10 μm for length. Unmodified and optimised HMT-BGS showed characteristic FTIR bands linked with common starches. All BGS samples displayed multiple vibrations in the region below 1000 cm^-1 due to the skeletal vibrations of the glucose pyranose ring.

Properties of potato starch as influenced by microwave, ultrasonication, alcoholic-alkali and pre-gelatinization treatments

The present study was framed to develop modified potato starch by various physical (microwave treatment, ultrasonication, pre-gelatinization) and chemical (alcohol-alkali) methods. Both native and modified starches were characterized on the basis of physicochemical, functional, and morphological attributes. Compared to native potato starch, modified starches exhibited improved water absorption capacity and water solubility index. The particle size of the starches was found to be in the range of 10.01-10.36 μm with negative zeta potential values. FTIR results revealed that modification in the peaks is attributed to the change in the structural configuration and re-organization of the microstructure between molecules of the starch during the treatments. The results of X-ray diffraction suggested that the typical peaks varied to a little extent with modifications and relative crystallinity was decreased for all treated starches. SEM Micrographs revealed the complete structural changes and irregularities in pre-gelatinized and chemically modified starches, whereas other modification methods maintained the structural integrity of starch granules. An increase in pasting temperature of modified starches represented a higher resistance to swelling and rupture, whereas rheologically, starches exhibited non-newtonian behavior with the shear-thinning property. Thus, the characteristics of modified starches will assist in the selection of potato starch for better applications in the food industry.

Thermal properties of different types of starch: A review

Starch is present in high amount in various cereals, fruits and roots & tubers which finds major application in industry. Commercially, starch is rarely consumed or processed in its native form, thus modification of starch is widely used method for increasing its application and process stability. Due to the high demand for starch in industrial applications, researchers were driven to hunt for new sources of starch, including modification of starch through green processing. Thermal properties are significant reference parameters for evaluating the quality of starch when it comes to cooking and processing. Modification of starches affects the thermal properties, which are widely studied using Differential scanning calorimeter or Thermogravimetric analysis. It could lead to a better understanding of starch's thermal properties including factors influencing and expand its commercial applications as a thickener, extender, fat replacer, etc. in more depth. Therefore, the review presents the classification of starches, factors influencing the thermal properties, measurement methods and thermal properties of starch in its native and modified form. Further, this review concludes that extensive research on the thermal properties of new sources of starch, as well as modified starch, is required to boost thermal stability and extend industrial applications.

Variations of Nutrient and Antinutrient Components of Bambara Groundnut (Vigna subterranea (L.) Verdc.) Seeds

Bambara groundnut (BGN) fits the bill when it comes to an acceptable level of nutrient and mineral composition. BGN is a balanced food that can help eradicate food and nutritional insecurity if it is incorporated into the major food system. However, there is a large degree of variation in nutrient composition and antinutritional factors among BGN accessions. Here, we show the degree of variability of nutrient and antinutrient components such as percentage ash, moisture, protein, fat, tryptophan, tannin, and phytate contents in seeds of 95 accessions of BGN. Data were subjected to analysis of variance (ANOVA), followed by correlation and principal component analysis. Clustering was done to show the relatedness between the accessions in response to the various traits. A high level of heterogeneity was observed among the accessions for the various traits studied. PC1 and PC2 show 41.2% of the total observed variations. Cluster analysis grouped accessions into four main clusters. This study was able to confirm the high level of diversity in the components of nutrients and antinutrients previously reported in BGN. The results of this study are expected to aid in identifying parent lines for improved breeding programs.

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.

Effect of Single and Dual Modifications on Properties of Lotus Rhizome Starch Modified by Microwave and γ-Irradiation: A Comparative Study

A comparative study between two novel starch modification technologies, i.e., microwave (MI) and γ-irradiation (IR), is of important significance for their applications. The objective of this work is to compare the changes in lotus rhizome starch (LRS) subjected to single modifications by MI (thermal treatment) and IR (non-thermal treatment), and dual modification by changing the treatment sequence, i.e., microwave followed by irradiation (MI-IR) and irradiation followed by microwave (IR-MI). The amylose content of native and modified LRS varied from 14.68 to 18.94%, the highest and lowest values found for native and MI-LRS, respectively. IR-treated LRS showed the lowest swelling power (4.13 g/g) but highest solubility (86.9%) among native and modified LRS. An increase in light transmittance value suggested a lower retrogradation rate for dual-modified starches, making them more suitable for food application at refrigeration and frozen temperatures. Dual-modified LRS showed the development of fissures and dents on the surface of granules as well as the reduction in peak intensities of OH and CH2 groups in FTIR spectra. Combined modifications (MI and IR) reduced values of pasting parameters and gelatinization properties compared to native and microwaved LRS and showed improved stability to shear thinning during cooking and thermal processing. The sequence of modification also affected the rheological properties; the G′ and G″ of MI-IR LRS were lower (357.41 Pa and 50.16 Pa, respectively) than the IR-MI sample (511.96 Pa and 70.09 Pa, respectively), giving it a soft gel texture. Nevertheless, dual modification of LRS by combining MI and IR made more significant changes in starch characteristics than single modifications.

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.

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.

Microwave treatment alters the fine molecular structure of waxy hull-less barley starch

Waxy hull-less barley kernels and their isolated starches were exposed to different microwave conditions (power 640, 720, and 800 W, time 60, 120 and 180 s) and changes in morphology, particle size, digestibility, rheological properties, and molecular structure were measured and analyzed. Microwave treatment caused roughness and deformation of granular surfaces, and an increase in granule size. After treatment, the in vitro digestibility of starch was increased, i.e., the RDS increased, but the RS decreased. Microwave treatment decreased the K values of the in-kernel MWI WHBS. Dynamic rheological results showed that the in-kernel MWI WHBS pastes had lower T_G'max, and higher G'_max, G'_90°C, G'_25°C, G'_0.1Hz and G'_20Hz after treatment. The chain-length distribution did not significantly change after microwave treatment. However, the results for molecular size distributions showed that the peaks of amylopectin (R_h = ~100 nm) shifted left and right, indicating that the molecular volume might become smaller or larger under different processing conditions. The primary effects of microwave treatment may be loosening the molecular structure and cutting main chains of amylopectin.

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.

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

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

Effect of starch microstructure on microwave-assisted esterification

Dry modification of starch, especially by microwave-assisted heating, has attracted increasing attention due to its various advantages, including energy saving, high conversion, rapidity, and avoidance of volatile organic solvents in organic synthesis. This work focuses on two fundamental issues: 1) effect of starch microstructure on dry modification; 2) effect of acid anhydride in solid and liquid states on the dry reaction, since their interfaces with solid starch are significantly different. Cornstarches with different amylose/amylopectin ratios were used to demonstrate the effect of starch microstructure, while two acid anhydrides, maleic (solid) and acetic (liquid) anhydrides, were used to study the reaction mechanisms. FTIR, SEM, XRD, and DSC were used to study the performance of modified starches and the mechanisms. It was found that the degree of substitution (DS) of starches modified by maleic anhydride generally increased with increasing amylose content since amylose contains more hydroxyl groups, resulting in higher sensitivity to microwaves. On the other hand, the DS of starches modified by acetic anhydride increased with increasing amylopectin content, since liquid acetic acid can diffuse into high-amylopectin starch granules. The higher amylopectin starches, waxy and maize, showed higher RC(%) and ∆H(%) than that of higher amylose starches G50 and G80.