Structural Modification of Rice Bran Arabinoxylan by Extrusion Improves Digestion Susceptibility and Microbial Fermentability

Gut microbial utilization of rice bran arabinoxylan (AX) is strongly shaped by fiber matrix structure and gastrointestinal digestion. This study investigated how extrusion-induced structural modification of rice bran affects the digestion susceptibility, fine structure, and microbial fermentability of AX. Arabinoxylan extracted from native rice bran (RB-AX) and extruded rice bran (RB-Ex-AX) were characterized before and after simulated upper gastrointestinal digestion in terms of microstructure, composition, and glycosidic linkage patterns. Their prebiotic potential was further evaluated using in vitro human fecal fermentation by monitoring gut microbiota composition and short-chain fatty acids (SCFA) production. Extrusion disrupted the fiber matrix, generating a more porous structure while FT-IR spectra indicated no major change in the characteristic AX backbone functional groups. Although RB-AX and RB-Ex-AX showed relatively similar monosaccharide profiles before digestion, simulated digestion caused a 15% greater reduction in glucose content in RB-Ex-AX, accompanied by a relative increase in arabinose and xylose residue. Glycosidic linkage analysis revealed decreased T-Glc p and 4-Glc p linkage and increased 2,3,4-Xyl p residues, indicating relative enrichment of xylan backbone structure. These digestion-mediated structural changes enhanced microbial fermentation, as RB-Ex-AX produced significantly higher total SCFAs during the late fermentation phase (12–24 h) and selectively enriched Bacteroidota , particularly Bacteroides , Segatella and Parabacteroides .