Physicochemical and microstructural characteristics of canola meal fermented by autonomously screened Bacillus licheniformis DY145 and its immunomodulatory effects on gut microbiota

Canola meal (CM), a variety of double-low rapeseed meal (RSM), is a valuable protein source due to its reduced glucosinolate (<20 μmol/L) and erucic acid (<2 %) content. In this study, bioactive small peptides were derived from CM through fermentation with an autonomously screened Bacillus licheniformis DY145 strain. Strain mutagenesis and fermentation condition optimization further enhanced peptide activity. The physicochemical and microstructural changes in fermented canola meal (FCM) were analyzed, and the immunomodulatory effects of active peptides on lipopolysaccharide (LPS)-induced inflammatory mice were investigated. Fermentation significantly increased the soluble peptide concentration and DPPH radical scavenging capacity of CM (P < 0.05), while reducing protein molecular weight and glucosinolate content (P < 0.05). Scanning electron microscopy revealed a loose structure in CM after fermentation, and canola peptides (CPs) from fermented CM exhibited higher zeta potential, a reduced α-helix ratio, and lower fluorescence intensity compared to those from unfermented CM. Structural characterization of CPs was performed using LC-MS/MS, followed by bioactivity analysis. CPs significantly downregulated serum levels of TNF-α, IL-6, and IL-1β in LPS-induced mice (P < 0.05), while upregulating IgA and IgG levels (P < 0.05). Moreover, CP supplementation restored the gut microbial composition, normalizing dominant flora and increasing Lactobacillus abundance (P < 0.05). This study demonstrates the potential of CPs as functional food ingredients to mitigate gut inflammation and enhance the high-value utilization of CM. Additionally, it introduces a novel strain and fermentation method for bioactive peptide production, providing a theoretical foundation for the development of gut health-promoting functional foods. Furthermore, the preliminary structure-activity relationship analysis of CPs lays the groundwork for designing peptides with gut microbiota-modulating properties.