Effects of thermal sterilization on soy protein isolate/polyphenol complexes: Aspects of structure, in vitro digestibility and antioxidant activity

The main purpose of this work was to investigate the influence of typical thermal sterilization approaches (pasteurization, high-temperature sterilization) on the structure, in vitro digestibility , and antioxidant activity of soy protein isolate (SPI)/black soybean seed coat extract (BE) complexes at pH 7.0. The results of zeta potential and particle size demonstrated that the addition of BE was contributed to inhibit protein thermal aggregation. Heat sterilization resulted in protein unfolding revealed by UV–Vis, circular dichroism , and fluorescence spectroscopy analysis. The increase of BE led to the reduction of fluorescence intensity and surface hydrophobicity of SPI. Moreover, the formation of SPI/BE complexes inhibited protein digestion in vitro, while thermal sterilization promoted protein digestion. The SPI/BE complexes showed a strong radical scavenging ability both before and after thermal treatment.