Production and characterization of novel antioxidant peptides from mulberry leaf ferment using B. subtilis H4 and B. amyloliquefaciens LFB112

The objective of this study was to isolate and characterize antioxidant peptides from mulberry leaves fermented with Bacillus subtilis H4 and Bacillus amyloliquefaciens LFB112. The results indicated that fraction F4 (<1 kDa) exhibited superior DPPH activity compared to the F1 (>10 kDa), F2 (3-10 kDa), and F3 (1-3 kDa) fractions, and cytoprotective effect against lipopolysaccharides (LPS)-induced oxidative stress in RAW264.7 cells. Three novel peptides, FRFDP, RFGG, and GPPLAFGGGP, were identified in the F4 fraction of the mulberry leaf ferment, and docking results showed that these peptides could form stable carbon (covalent) and hydrogen bonds to the active sites of Keap1, thus regulating the Keap1-Nrf2 pathway by blocking the Nrf2 binding sites on Keap1. These peptides significantly upregulated the mRNA expression of Nrf2, HO-1, and NQO1, providing indirect evidence of their potential to enhance cellular antioxidant defense via the possible activation of Keap1-Nrf2 pathway. Furthermore, these peptides showed good DPPH and ABTS scavenging activities, indicating their potential as antioxidant peptides. This study offers valuable insights into the integration of these novel peptides in developing mulberry leaf ferment as a functional food and their potential use as a feed additive.