Soybean protein is widely used as a high-quality plant protein in the food industry, due to its multiple functional properties. However, the high-activity lipoxygenase is easy to catalyze the lipid peroxidation of polyunsaturated fatty acids during the processing of soybean products. A large number of reactive oxygen species and secondary oxidation products can also be produced to further induce protein oxidation. The structure and function of proteins are closely related to the oxidation that is accompanied by the changes in protein solubility, water retention, gel, and emulsification functional properties, thus leading to the processing properties of proteins. Fortunately, microwave processing can be expected to alter the spatial structure of proteins and intermolecular forces. The reaction groups can be exposed to be originally embedded in the protein molecules, resulting in changes in their structure and functional characteristics. Taking the soybean protein oxidized aggregates as the raw materials, this work aims to clarify the effect of microwave treatment time on the functional characteristics and structure, such as solubility, emulsification, and foaming. The protein functional properties were then improved without the use of biochemical reagents, high-pressure, or radiation treatment, thereby expanding the protein applications without the wastes of food resources. An oxidization reaction was constructed with the soy protein and AAPH (2,2'-azobis(2-methylpropionamidine) dihydrochloride). Different irradiation durations (0, 10, 20, 30, 40, 50, 60, and 70 s) of the microwave with a power of 350 W were used to investigate the effect of microwave treatment on the structural characteristics (particle size distribution, turbidity, secondary structure, and microstructure) and processing properties (solubility, water-holding capacity, oil-holding capacity, foaming and foam stability, emulsification and emulsion stability) of oxidized aggregated soy protein. The results showed that the oxidation induced the formation of larger particle size, higher molecular weight, and more compact protein aggregates, which simultaneously damaged the processing properties. Microwave treatment for an appropriate time (<30 s) induced the polarization of protein isolate molecule. There was damage to the non-covalent bond that maintained the protein spatial structure. The protein isolate molecules were partially unfolded to expose the internal hydrophobic residues on the protein surface, thus promoting the formation of the water-air interface. At the same time, the interaction between that extensin molecules formed a more stable interfacial facial mask, thereby improving the foaming, emulsifying, water, and oil-holding properties. Microwave treatment for a long time (>30 s) promoted the further expansion of soy protein isolate molecules, and further exposure inside the hydrophobic and sulfhydryl groups. As such, the larger molecular aggregates were formed between depolymerized protein molecules through noncovalent bonds. There was an increase in the particle size, turbidity, and disordered structure, whereas, a decline in the stability of the interfacial facial mask, thus leading to the decline of functional properties. Consequently, the physical field of microwaves can be expected to modulate the functional properties of soy protein. Specifically, the structural and aggregation behavior can be altered to improve the functional properties of soy protein for the better behavior of soy protein oxidation aggregates using microwaves. The finding can also provide a strong reference for microwave processing in the field of food production.

Plant-based meat was prepared from soy protein concentrate (SPC) with different proportions of added sodium alginate (SA) by twin screw high-moisture extrusion under varying die temperature. The macrostructure and microstructure of plant-based meat were characterized by texturization degree, chewiness, color, and scanning electron microscopy. The structural properties of the extrudates were investigated by specific mechanical energy, cooking characteristics, and water absorption capacity. The results showed that the addition of sodium alginate could improve the texturization degree and enhance the chewiness of extrudates. And all extruded samples obtained at a die temperature of 150 ℃ had a higher texturization degree. The specific mechanical energy and water absorption capacity showed that sodium alginate enhanced the protein-protein and protein-water interactions, and consequently increased the water holding capacity of the extrudates. Scanning electron microscopy showed that excessive sodium alginate caused the product to form a dense lamellar, non-fibrous structure. As a result, we found that extrudates with 6% SA had the most abundant fibrous structure and good cooking performance.

This study was conducted to explore the effect of ultrasonic pretreatment on the structure and function of non-covalent/covalent complexes of soybean protein isolate (SPI) and catechin. SPI was pretreated with ultrasound before non-covalent/covalent binding to catechin at different pH conditions (3.0, 7.0, 9.0 and 12.0), Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) was used to verify the formation of complexes and the binding degree between protein and polyphenols. Meanwhile, fluorescence spectroscopy, Fourier transform infrared (FTIR) spectroscopy and molecular docking were used to study the interaction between SPI and catechin. The changes in functional properties ofthe complexes were investigated in terms of foamability, foam stability, solubility, turbidity, and antioxidant capacity. The SDS-PAGE profile confirmed the formation of non-covalent/covalent complexes, and that ultrasonic pretreatment could affect the degree of binding. It was found that the highest amount of catechin was bound to ultrasonicated SPI at pH 12. Fluorescence and FTIR spectra indicated that the secondary structure of SPI in the non-covalent/covalent complexes was changed. Compared to the untreated SPI sample, the proportions of α-helix and β-sheet decreased, the proportions of β-turn and random coil increased, and the numbers of exposed tryptophan and tyrosine residues increased. The most significant effect of ultrasonic pretreatment was observed at pH 12; the proportion of β-turn increased to 40.20%, the proportion of random coil increased to 28.61%, and SPI’s structure became unfolded and loosened. After ultrasonic pretreatment, compared to the untreated SPI sample, the solubility, turbidity, foamability, foam stability and antioxidant capacity of SPI and complexes increased. In particular, the scavenging capacity against 1,1-diphenyl-2-picrylhydrazine (DPPH) radical and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation of complexes formed at pH 12 were up to 5.5 and 4.8 times of the untreated SPI sample, respectively. In addition, the molecular docking results revealed that the main non-covalent binding interactions between SPI and catechin were hydrogen bonds and hydrophobic interactions. To sum up, ultrasonic-treated SPI had the strongest binding strength to catechin at pH 12, and the resulting covalent complex had the best stability as well as significantly improved foamability and antioxidant activity.

The quality of naturally fermented maize flour, unfermented maize flour and maize flour fermented with Lactobacillus plantarum (Lp) and/or Saccharomyces cerevisiae (Sc) was analyzed by using unfermented maize flour as the control.The results showed that the contents of crude protein, crude fat, crude fiber and crude ash in fermented maize flour were significantly lower (P < 0.05) and the content of total starch was significantly higher (P < 0.05) when compared with unfermented maize flour.Fermentation increased the pasting temperature of maize flour significantly (P < 0.05), the breakdown and setback values of naturally fermented and Lp + Sc fermented maize flour were significantly lower than those of unfermented maize flour (P < 0.05), and the stability and anti-retrogradation ability of maize flour were improved.Moreover, fermentation with Lp and Lp + Sc had a pronounced effect on the structure of maize flour, while during fermentation with Sc and Lp + Sc, aroma compounds and metabolites which could improve the off-odor of fermented maize flour were produced.The fermentation periods of maize flour with Lp, Sc and their combination were 72, 18 and 48 hours, respectively compared to 13 days for natural fermentation.Maize flour fermented with Lp + Sc had better quality, flavor and processing properties.

In this study, natural soybean oil body emulsion and pectin were combined by electrostatic deposition for the preparation of soybean oil body-pectin composite oleogel by emulsion template method. The macro- and micro-structures of soybean oil body-pectin composite oleogel were studied, and the average particle size, zeta potential, oil binding capacity, re-dissolution stability, rheological properties, texture properties and oxidative stability were analyzed. The results showed that the average particle size and zeta potential of the composite emulsion containing 1.0% of pectin (m/m) were both smallest and were 423.13 nm and −23.23 mV, respectively. Cryoscanning electron microscopy (Cryo-SEM) showed that with an increase in pectin concentration, the structure of the sample was more compact, the hardness of the freeze-dried sample increased, and the gel strength of the oleogel increased; it showed shear thinning and good thixotropy. In addition, the addition of pectin could significantly improve the oxidative stability of oleogels. Notably, the oleogel containing 1.0% or more of pectin had good re-dissolution stability, and the average particle size and zeta potential of the obtained emulsion were not significantly different from those of the initial emulsion. The three-dimensional network structure was restored to its initial state after dilution and shearing with the same mass of distilled water, and this process was reversible. Therefore, the new stable oleogel prepared with soybean oil body is a potential alternative to artificial solid fat.