Subtle structural variations of resistant starch from whole cooked rice significantly impact metabolic outputs of gut microbiota

While cooked rice is widely consumed as a whole food, the specific characteristics and impact of its resistant starch (RS) on gut microbiota are largely unexplored. In this study, three rice varieties with distinct starch molecular structures were used to prepare RS from cooked rice. All three types of RS had a crystalline structure characterized as B + V type, with the V type being the predominant crystalline polymorph. Distinct differences in chain-length distributions were observed among different RSs, with rapidly fermentable starch fractions comprising short amylopectin and long amylose chains, while the degrees of polymerization (DPs) ~ 10, 37, 65, and 105 fractions comprised the slowly fermentable starch. Jasmine rice RS showed the highest proportion of this slowly fermentable starch fraction, which appeared to be specifically utilized by Megasphaera_elsdenii_DSM_20460 OTU198. The fermentation of Jasmine RS resulted in the highest production of butyrate after 24 h, which was positively correlated with the relative abundance of Megasphaera_elsdenii_DSM_20460 OTU198. These findings collectively indicate that RS in cooked rice with a higher V type crystallinity and DPs ~ 10, 37, 65, and 105 fractions promote butyrate production and stimulate the growth of butyrate-producing bacteria in the human gut, thereby conferring beneficial effects on gut health.