Gelatinization differentially impacts in vitro fermentation of high-amylose maize starch

Some of the starch in a meal, depending on how it was thermally processed, may escape complete digestion in the upper gut and pass into the colon as available for microbial fermentation. This study uses an in vitro batch fecal model to examine the fermentability of high-amylose maize starch (HAMS) that has been gelatinized to different degrees (DG). Compared with native HAMS, more gases and acids were produced from gelatinized HAMS during the initial 4 h of fermentation, which was attributed to the stronger binding of bacteria to gelatinized HAMS. At the endpoint of fermentation, HAMS and HAMS with a DG of 22.8% (DG22.8) yielded more butyrate, whereas HAMS with DG ≥ 45.5 generated more acetate and propionate. The characteristics of SCFA production from fermentations of HAMS with different DG were associated with the enrichment of specific SCFA-producing bacterial species. There were no apparent differences in gas and acid production, and composition of the microbiota, in fermentations of HAMS with DG ≥ 45.5, although proliferation of pathobionts (Escherichia_Shigella and Collinsella) was noted compared to HAMS and HAMS-DG22.8. Our study showed that the amount of gelatinized starch in the fermentation substrate significantly affected fermentation behavior, with higher proportions of gelatinized starch available for colonic fermentation potentially having negative effects on the gut health.