Dual isoflavone and carboxyl-containing compound profiling for antioxidant evaluation of fermented soybean products

Fermented soybeans are functional foods with both medicinal and nutritional value and contain major antioxidant-related constituents, including isoflavones and carboxyl-containing compounds (CCCs). Qualitative and quantitative analyses of isoflavones and CCCs were performed using HPLC-DAD and DIAAA-derivatization UHPLC-Q-TOF/MS, respectively, to characterize the dynamic changes in these compounds during fermentation. Isoflavones have traditionally been used as antioxidant-related markers for fermented soybeans. Three isoflavones (daidzein, glycitein, and genistein) have been used as markers to enable partial optimization of fermentation conditions. Furthermore, six CCCs (Ala-Trp, asparagine, tryptophan, histidine, valeric acid, and isobutyric acid) were identified as additional markers based on their significant variation under different fermentation conditions, complementing isoflavones as the only antioxidant-related markers. The antioxidant activity of these compounds was validated by DPPH and ABTS radical scavenging assays. Several dual isoflavone and CCCs profiling models were proposed, and their specificity and sensitivity for antioxidant-related marker evaluation were assessed using receiver operating characteristic curves. Ultimately, a strategy that integrated isoflavones with CCCs was shown to be more effective for optimizing fermentation conditions. This study proposes a dual antioxidant-related marker strategy for optimizing the fermentation process, provides a new approach for assessing antioxidant-related marker attributes of fermented soybeans and supports further fermented foods' nutraceutical development.