In vitro fecal fermentation characteristics of starch-chitosan composite prepared by screw extrusion

In this study, we prepared a series of composites with various chitosan-to-starch ratios by means of screw extrusion. The morphology and structural order of the composite were examined, and the fermentability was investigated through an in vitro human fecal fermentation model. Fourier transform infrared (FTIR) spectroscopy demonstrated the formation of hydrogen bonds between starch and chitosan in the composite, and X-ray diffraction (XRD) analysis indicated the structural order of the composite was enhanced with increasing chitosan proportions. The addition of chitosan slowed down the pH drop rate during the fermentation, and high chitosan proportion decreased the production of short-chain fatty acids (SCFAs), especially butyrate. The final butyrate concentrations of the composite with chitosan to starch ratio of 1:6 (CS:S = 1:6, 0.97 mmol/g) was almost twice that of the composite with chitosan to starch ratio of 2:1 (CS:S = 2:1, 0.51 mmol/g). Health-promoting microbes including Agathobacter, Prevotella_9, Ruminococcus, and Bifidobacterium were obviously promoted by extruded starch. Moreover, the composite sample with chitosan to starch ratio of 1:6 (CS:S = 1:6) exhibited a good synergistic effect in regulating the microbiota composition, reflected by the increase in the relative abundance of Agathobacter and Prevotella_9. This finding demonstrated that the ratio of starch to chitosan might be a controlling factor in determining the fermentation properties of screw extruded composite.