Characterization of Various Noncovalent Polyphenol–Starch Complexes and Their Prebiotic Activities during <i>In Vitro</i> Digestion and Fermentation

Abstract

This study explores the structural characterization of six noncovalent polyphenol-starch complexes and their prebiotic activities during <i>in vitro</i> digestion and fermentation. Ferulic acid, caffeic acid, gallic acid, isoquercetin, astragalin, and hyperin were complexed with sweet potato starch (SPS). The polyphenols exhibited high binding capacity (>70%) with SPS. A partial release of flavonoids from the complexes was observed via <i>in vitro</i> digestion, while the phenolic acids remained tightly bound. Molecular dynamics (MD) simulation revealed that polyphenols altered the spatial configuration of polysaccharides and intramolecular hydrogen bonds formed. Additionally, polyphenol-SPS complexes exerted inhibitory effects on starch digestion compared to gelatinized SPS, owing to the increase in resistant starch fraction. It revealed that the different complexes stimulated the growth of <i>Lactobacillus rhamnosus</i> and <i>Bifidobacterium bifidum</i>, while inhibiting the growth of <i>Escherichia coli</i>. Moreover, <i>in vitro</i> fermentation experiments revealed that complexes were utilized by the gut microbiota, resulting in the production of short-chain fatty acids and a decrease in pH. In addition, the polyphenol-SPS complexes altered the composition of gut microbiota by promoting the growth of beneficial bacteria and decreasing pathogenic bacteria. Polyphenol-SPS complexes exhibit great potential for use as a prebiotic and exert dual beneficial effects on gut microbiota.