Screening of antioxidant peptides from soy protein isolate: In vitro activity validation and structure-activity relationships investigation through quantum chemical calculations

Soy protein isolate (SPI) holds significant potential for providing antioxidant peptides. In this study, we optimized the hydrolysis conditions to obtain SPI hydrolysates with high antioxidant activity. Subsequently, we isolated, identified and screened three antioxidant peptides through ultrafiltration, liquid chromatography-tandem mass spectrometry and bioinformatics methods, respectively. Among them, DHHDPIMPYL demonstrated higher antioxidant activity. Quantum chemical analysis further revealed the key antioxidant activity sites as N1-H2 for SPDIFNPQ, N1-H2 for SSPDIFNPQ, and O145-H146, N48, and S107 for DHHDPIMPYL. Additionally, these antioxidant peptides maintained cellular redox balance by clearing reactive oxygen species (ROS), increasing the ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG), and activating glutathione peroxidase (GSH-Px) activity. Our results highlight the value of quantum chemistry methods in elucidating the antioxidant mechanisms of peptides and support the potential application of SPI-derived peptides as promising antioxidants in the food industry.