Isomeric effect of coumaric acid on the structure, digestion, and gut microbiota regulation of starch-based V-type complexes

This study investigated the interaction between three coumaric acid isomers (para-, meta-, and ortho-CA) and corn starch under high-pressure processing. Isomer position critically influenced the multi-scale structure, digestibility, and gut microbiota-modulating function of the resulting complexes. All isomers formed V -type inclusion complexes within the starch helices, with para-CA conferring stronger binding affinity and more compact structures. This structural recombination significantly increased the content of resistant starch (up to 68.43 ± 0.16% with 20% p-CA), while reducing rapidly digestible starch (9.76 ± 0.19%), resulting in the estimated glycemic index decreasing in the order of para < ortho < meta-coumaric acid. During in vitro fecal fermentation, these complexes exhibited slow release of encapsulated polyphenols over 24 h, significantly boosting short-chain fatty acid (especially acetic acid) production, lowering pH value, and selectively regulating gut microbiota (a reduced Firmicutes / Bacteroidetes ratio and an increased abundance of beneficial genera such as Bifidobacterium ). These findings provide a theoretical basis for designing targeted starch-based functional foods for precise glycemic control and gut health promotion.