Characterization and in vitro digestion of rice starch/konjac glucomannan complex prepared by screw extrusion and its impact on gut microbiota

In this paper, we prepared a series of rice starch complexed with various konjac glucomannan (KGM) contents under screw extrusion. The complex's multi-scale structures, rheological and thermal properties, and in vitro digestion were explored. The complex's effects on short-chain fatty acids production and gut microbiota composition were further investigated using in vitro human fecal fermentation. Multi-scale structural analysis indicated that short-ordered degree, single/double helix structure contents, and crystallinity of the rice starch increased with an increased concentration of KGM. Rheology and differential scanning calorimeter analysis indicated that KGM enhanced the viscoelasticity of rice starch paste and the thermal stability of rice starch. In vitro digestion data revealed that as KGM concentrations increased, both slowly digested component (SDC) and resistant component (RC) contents increased. This phenomenon was ascribed to the complexation of KGM with rice starch assisted by screw extrusion. Further, the high RC content of the complex contributed to the yield of butyrate level, corresponding to the growth in Actinobacteria at the phylum level, and Megasphaera and Bifido-bacterium at the genus level in the cultures. Overall, this research will be critical in determining the physico-chemical properties and fecal fermentation behaviors of the rice starch-KGM complex and creating starchy foods with specific health benefits.