Mechanistic insights into the Bacillus subtilis K6 solid-state fermentation-induced structural transformation and enhanced bioactivity of flaxseed meal dietary fiber

Flaxseed meal (FSM), an oil-processing byproduct rich in dietary fiber (DF), was subjected to solid-state fermentation (SSF) using Bacillus subtilis K6. This study systematically examined structural modifications and in vitro bioactivities of soluble (SDF) and insoluble dietary fiber (IDF) fractions before and after fermentation. SEM and FTIR analyses showed degradation of cellulose and hemicellulose during SSF, yielding a more porous structure. XRD and TGA indicated disrupted crystalline regions in SDF and IDF, with fermented IDF (F-IDF) exhibiting enhanced thermal stability. SSF altered monosaccharide composition and reduced DF molecular weight. Transcriptomics revealed pentose and glucuronate interconversions and starch and sucrose metabolism as primary DF dissociation pathways, dominantly mediated by extracellular hydrolases. In vitro assessments demonstrated F-IDF's superior glucose adsorption capacity, whereas fermented SDF (F-SDF) exhibited greater cholesterol adsorption, pancreatic lipase inhibitory activity, nitrite adsorption capacity, and sodium cholate binding capacity. These findings provide a theoretical basis for FSM-derived DF utilization.