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To investigate the impact of frozen storage conditions on the physicochemical properties of soybean protein and explore the underlying mechanisms, this study focused on soybean isolate (SPI), ß-soybean companion globulin (7S), and soybean globulin (11S). The protein solutions were prepared at a concentration of 2% and subjected to freezing for 1 and 5 days. Subsequently, the protein content, physicochemical properties, secondary structure, sulfhydryl content, and chemical interaction forces were assessed and analyzed using UV spectrophotometry, Zeta potential measurements, SDS-PAGE, Fourier infrared spectroscopy, and endogenous fluorescence photoemission spectroscopy. The obtained results revealed that the solubility and total sulfhydryl content of SPI, 7S, and 11S exhibited a decreasing trend with prolonged freezing time. Among them, 11S demonstrated the largest decrease in solubility and total sulfhydryl content, followed by SPI, and 7S the least. During freezing, the aromatic amino acids of SPI, 7S, and 11S molecules were exposed, leading to increased hydrophobicity, protein aggregation, and particle size enlargement, and the structure of the protein changed from disordered structure to ordered structure. After freezing, the polarity of the microenvironment of SPI, 7S, and 11S increased, and their maximum fluorescence emission wavelengths were red-shifted. Notably, the largest red shift of SPI was from 332 nm to 335 nm. As freezing time increased, the contribution of hydrogen bonding increased, while the contribution of hydrophobic interactions decreased. This indicates that freezing affects the hydrophobic interactions, hydrogen bonding, and other chemical forces of the protein. The growth of ice crystals leads to the unfolding of protein molecular chains, exposure of internal hydrophobic groups, enhancement of hydrophobicity, and alters the secondary structure of the protein. [ABSTRACT FROM AUTHOR]

This study aimed to analyze the dynamic evolution of physicochemical properties and microstructure in soybean protein gels subjected to freezing conditions. SPI, 7S, and 11S were used in experiments. A 12g/100g protein gel was formulated after 1 and 5 days of freezing. Subsequent determination and analysis encompassed various indices, including texture, subunit composition, sulfhydryl group content, water distribution, and microstructure. The findings revealed a significant increase in the hardness of SPI, 7S, and 11S protein gels with prolonged freezing time. The 11S gel exhibited the most substantial increase, followed by SPI and 7S. And the decreases in the water-holding properties of the protein gels were 10.08%, 1.19%, and 49.34%, with the largest decrease in the water-holding properties of the 11S protein gels. Conversely, the water-holding capacity and total sulfhydryl content of SPI, 7S, and 11S protein gels decreased over time during freezing. Subunit distribution analysis indicated darker bands at the top of concentrated and separation gels. The freezing process induced the formation and growth of ice crystals, altering the spatial network structure of protein gels. Consequently, the proportion of free water in all three soybean protein gels increased, leading to enhanced mobility and a looser network structure. [Display omitted] • Effect of freezing on the properties of soy protein (SPI, 7S, 11S) gels. • Establishing a link between soy protein gels properties and structure after freezing. • Elucidation of difference mechanism in soy protein gels properties during freezing. [ABSTRACT FROM AUTHOR]

To study the causes of beany off‐flavor regeneration after fermented soymilk was thermal treated. Hexanal was soymilk beany off‐flavor and analyzed using headspace solid phase microextraction. The hexanal removal and regeneration during fermentation and heat treatment of soymilk and soy protein solutions were analyzed. Soymilk contained both free and protein‐bound hexanal. Both 7 S and 11 S could bind to hexanal, and the amount of bound hexanal to 11 S was approximately five times that to 7 S. pH decreased to approximately 4.5 or enzymatic hydrolysis could effectively weaken the binding of hexanal to soy protein, but not capable of dissociating them. Further heat treatment was required for hexanal volatilized from protein. Lactic acid bacteria could completely remove free hexanal, but the removal ability of protein‐bound hexanal was weak, which varied among bacterial species. The results will be valuable for improving flavor qualities of fermented soymilk and its beverage products. This result revealed the mechanism behind the fact that the off‐flavor of heated fermented soymilk was difficult to be removed. Thus, the results will be valuable for improving flavor qualities of fermented soymilk and its beverage products. Practical applications: This result revealed the mechanism behind the fact that the off‐flavor of heated fermented soymilk was difficult to be removed. Thus, the results will be valuable for improving flavor qualities of fermented soymilk and its beverage products. [ABSTRACT FROM AUTHOR]

The functional properties (elasticity and water holding capacity) of soy protein isolate (SPI) are degraded by denaturalization during frozen storage. To solve this problem, a modified SPI was prepared by cross-linking SPI and gelatin with transglutanminase (TGase). The gel properties of the modified SPI were analyzed during frozen storage. After 20 days of frozen storage, the water holding capacity (WHC) of the SPI gels decreased from 89% to 65%, whereas that of the modified soybean protein isolate (MSPI) gels remained above 85%, which was 29.6% higher than that of the SPI gels. In addition, the hardness increment of the MSPI gels only accounted for 47.1% that of the SPI gels. The moisture distribution of the MSPI gels showed no significant change during frozen storage, and the content of unfreezing water in the MSPI gels was higher than that in the SPI gels. Confocal laser scanning microscopy revealed that the microstructure of the MSPI gels suffered minimal damage after frozen storage, whereas that of the SPI gels presented a honeycomb pattern after frozen storage. Analysis of soluble protein, total SH groups, and gel chemical interaction showed that the improvement of MSPI gel properties during frozen storage was due to the slight decrease in the amount of gel soluble proteins and total SH groups and to the chemical interaction among different gels. [ABSTRACT FROM AUTHOR]