Structure of In Vitro Digestion Residues from High-Amylose Starch Impacts Colonic Microbial Composition and Metabolic Activity

Resistant starch (RS) is a nondigestible carbohydrate that serves as a prebiotic and is fermented by colonic bacteria to produce short-chain fatty acids (SCFAs). Here, in vitro digestion-derived residues (RSs) from five high-amylose starches (HASs; four RS2 and one RS3) were evaluated for their effects on microbiota composition and SCFA production using a simulated colonic fermentation model inoculated with human fecal microbiota. RSs with more amorphous structures and lower short-range order generated the highest SCFA levels and promoted the growth of the primary RS degrader Bifidobacterium adolescentis. In contrast, RSs with higher resistance to digestion and retained B-type crystallinity favored propionate-associated taxa, including Veillonella spp. and Bacteroides spp., whereas less resistant RSs promoted butyrate-producing taxa such as Clostridium spp. These results suggest that structural features of RS are associated with differences in microbial composition and metabolic activity, providing insights into the design of HAS-based dietary fibers with targeted prebiotic functions.