Molecular features of corn bran arabinoxylan regulate rice starch digestion and fermentability of arabinoxylan-starch digesta

Arabinoxylan (AX) modulates starch digestibility through hydrocolloid-mediated interactions, but its effect on the fermentation of starch digestion products remains unclear. Alkaline-extracted corn bran AX yielded five fractions of varied Mw by graded ethanol precipitation: AX50, AX55, AX60, AX65, AX70; unfractionated AXmixed was the reference. Their effects on rice starch pasting, in vitro digestion, and human fecal fermentation of native AX and AX-starch digesta (AX-D) were evaluated. All AX fractions reduced peak viscosity, suggesting restricted starch granule swelling. AX60 (apparent Mw = 3.40 × 10⁵ g/mol, A/X = 0.7) most strongly inhibited starch digestion, decreasing rapidly digestible starch by 10.1%. During fermentation, native AX enhanced acetate and propionate production, increasing total short-chain fatty acids (SCFAs) by 20.6-29.8 mM compared with the blank, and enriched Bacteroides-dominated polysaccharide utilizers (> 60%). AX-D retained acid-producing capacity and exhibited higher microbial diversity than AX, with Bacteroidota and Bacillota each accounting for approximately 30%. AX60-D showed favorable fermentability, producing 22.1 mM total SCFAs. Correlation analysis indicated that resistant starch content and SCFA production were not consistently related to Mw or AX solution viscosity alone. These findings support evaluating AX-starch matrices through both starch digestion and subsequent digesta fermentation.