Ozone treatment increase the whiteness of soy protein isolate through the degradation of isoflavone

The color of soy protein isolate (SPI) influences the appearance of products such as tofu and soymilk, consequently impacting consumer preferences. Typically, whiter-colored SPIs were more favorite. However, products currently manufactured in the industry predominantly exhibit a yellowish hue. In our study, the incorporation of gaseous ozone into the production process of SPI notably improved its appearance on color. Simultaneously, a reduction in the isoflavone content enriched in SPI due to ozone treatment was observed, suggesting a potential mechanism for improving the whiteness of SPI. In addition, we discovered that the introduction of ozone for different times oxidized ozone-sensitive sulfhydryl groups, tryptophan, and tyrosine in proteins, thereby affecting the protein structure. This finding was determined through the analysis of free sulfhydryl groups, disulfide bonds, SDS-PAGE electrophoresis, FTIR, and endogenous fluorescence spectroscopy of SPIs. Meanwhile, the ozone treatment did not induce protein aggregation or alter its functional properties.