Multi-scale structural evolution and fermentation characteristics of four types of lentil resistant starches by human...

The multi-scale structural evolution and fermentation characteristics of four types of lentil resistant starch (RS2, RS3, RS4, RS5) were examined during vitro human fecal fermentation. Structural analyses indicated a significant reduction in molecular weight for RS2, RS4, and RS5. Crystalline forms were maintained in RS2 (C-type), RS3 (B-type), and RS4 (A-type), whereas RS5 (V-type) underwent a polymorphic transition to an A-type crystalline pattern. Increases in double-helical order and relative crystallinity were observed in RS2 and RS4, indicating preferential microbial degradation of amorphous regions. Scanning electron and confocal laser microscopy revealed extensive structural deterioration, including pitting, surface erosion, and internal fragmentation in RS2, RS4, and RS5, whereas RS3 exhibited only minor surface alterations. Short-chain fatty acid production was highly dependent on specific multi-scale structural features, including crystalline polymorph, molecular weight, and double-helical order. RS2 generated the highest levels of acetate and propionate, whereas RS3 yielded the greatest quantities of butyrate and valerate. Although microbial diversity decreased across all RS groups, distinct taxonomic changes were detected. Specifically, RS2 and RS4 promoted the growth of Ruminococcus, RS3 enriched Roseburia, and RS5 markedly stimulated Bifidobacterium and Megamonas. These findings demonstrate that the specific structure of resistant starch governs its fermentability, SCFA profile, and impact on microbial composition, highlighting the potential for structurally tailored RS to modulate gut health.