Strain-Specific Effects of Lactic Acid Bacteria Fermentation on Rice Bran: Physicochemical, Structural, and Metabolomic Analysis

• LAB fermentation significantly altered the physicochemical and structural properties of rice bran. • L. plantarum S58 excelled in acid production and comprehensive metabolic modulation. • L. brevis 03 enhanced antioxidant capacity and enzyme inhibitory activities. • LAB fermentation enriched functional components including GABA, phenolics, and flavonoids. • Strain-specific volatile and metabolic profiles were revealed by multi-omics analysis. Rice bran, a nutrient-rich agricultural byproduct, has not yet been fully utilized because it tends to become rancid and has poor storage stability. This study examined the impact of fermentation using three lactic acid bacteria (LAB) strains on the physicochemical attributes, structural features, and metabolomic profiles of rice bran. The findings indicated that LAB fermentation markedly lowered the pH and elevated titratable acidity, with Lactiplantibacillus plantarum S58 demonstrating the strongest acid-generating capability among the LAB. Additionally, fermentation significantly increased the levels of free amino acids (notably gamma-aminobutyric acid), short-chain fatty acids, total phenolic compounds, and flavonoids. These biochemical alterations resulted in a substantially enhanced antioxidant capacity (evaluated using ABTS, DPPH, and FRAP assays) and improved α-glucosidase inhibitory activity. Notably, rice bran fermented with Lactobacillus brevis 03 exhibited superior antioxidant performance, which was attributed to its comparatively higher concentrations of total phenolic compounds and flavonoids. Non-targeted metabolomic analysis identified a broad spectrum of differential metabolites predominantly associated with pathways related to amino acid metabolism, organic acid formation and nucleotide biosynthesis. Overall, this study clarifies the distinct regulatory influences of different LAB strains on the physicochemical behavior, structural organization, and metabolic networks of rice bran, thereby offering a scientific basis for targeted fermentation approaches and the development of high-value functional rice bran products.