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.
This study investigated the effects of enzyme action time (1–5 h) on the physicochemical properties, structure, and functionality of transglutaminase-catalyzed ovalbumin (OVA) in the presence of oligochitosan (OCS). Physically combining OVA and OCS led to a substantial increase in particle size and polydispersity index, rendering the mixed system unstable. With the increase of enzyme action time, the particle size of glycosylated and cross-linked OVA (GC-OVA) decreased first and then increased, reaching a minimum value of 411 nm at 4 h. Moreover, the decrease of free amino groups content at 4 h reflected the occurrence degree of glycosylation and cross-linking reaction, which was close to saturation. Diverse methods were used to analyze variations in the molecular structure of OVA, confirming changes in the primary, secondary, and tertiary structures, and the microstructure. The glycosylation grafting and cross-linking with the appropriate extent of the enzymatic action time is the primary reason for improving the foaming , emulsification properties, and DPPH activity of OVA. Moreover, GC-OVA had greater apparent viscosity, G′ and G″ than the other control systems (the untreated OVA and the physical mixture of OVA and OCS) and significantly affected the hardness and cohesion properties in the gel's texture (5.6 and 2.4-fold that of the untreated OVA, respectively). This study provides information for further understanding the effect of glycosylation grafting caused by enzyme cross-linking time on OVA. The study also demonstrates the possibility of obtaining new protein compositions to expand the applications of food proteins.
危险品化学品经营许可证（带存储）