Abstract
Soy protein is wildly used in food industry due to its high nutritional value and good functionalities. However, the poor storage stability of commercial soy protein products has puzzled both the producers and the users for a long time. The current study assessed the changes in protein solubility, aggregation, oxidation, and conformation of soy protein isolate (SPI) with various soluble aggregates formed at different pH values (pH 5–8) during storage. During storage, SPI samples showed a reduced protein solubility (p < .05), an increased protein oxidation (p < .05), and an attenuated conformational enthalpy (∆H). SPI with a higher pH produced more disulfide‐mediated aggregates at the expense of sulfhydryl groups and experienced greater losses of protein tertiary structure and a faster reduction in solubility. Yet, all samples nearly shared similar rising trend during 8‐week storage, which indicated the production of protein carbonyls was insensitive to pH. Soluble aggregates present in fresh SPI samples appeared to induce instability of SPI during storage. These findings suggested SPI prepared at pH 6 was in favor of its storage stability, and soluble aggregates presented in fresh samples should be paid more attention for further study of storage stability kinetics.
Highlights
Soy protein is widely used in food formulations, nutraceutical products, and beverages as an inexpensive functional and health-promoting ingredient (Wang, Liu, Ma, & Zhao, 2019)
We investigated the effect of pH on protein aggregation, oxidation, and solubility of soy protein isolate (SPI)
PH 5 SPI showed the lowest protein solubility throughout storage since the pH value is close to the isoelectric point of globulins in SPI (~pH 4.5) where protein solubility is always sensitive to small changes in the environment pH (Jiang et al, 2009)
Summary
Soy protein is widely used in food formulations, nutraceutical products, and beverages as an inexpensive functional and health-promoting ingredient (Wang, Liu, Ma, & Zhao, 2019). Soy protein isolate (SPI) solubility decreases by about 63% after 1-year storage at 42°C (Pinto et al, 2005). This insolubility of soy protein seriously affects its commercial applications because solubility plays an important role in the gelling and emulsifying properties of this functional ingredient (Hua, Cui, Wang, Mine, & Poysa, 2005). To meet the high demand of soy protein for food, nutraceutical, and beverage applications, several studies have been conducted to investigate the factors that might impact the structural and functional properties and the mechanism involving in storage instability of soy protein in the solid state. High RH and high temperature have been found to accelerate
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