Dietary fiber from sweet potato residue with different processing methods: Physicochemical, functional properties, and bioactivity in vitro

Dietary fibers (DF) were derived from unprocessed, physically processed (extrusion) and biologically processed (Lactobacillus fermentation) sweet potato residue, comprising soluble dietary fibers (C-SDF, E-SDF, F-SDF) and insoluble dietary fibers (C-IDF, E-IDF, F-IDF). Comparative analyses were conducted on the composition and physicochemical properties of three DFs. The functional properties and bioactivities of three SDFs were further investigated. Both physical processing and biological processing promoted the conversion of IDF into SDF and destroyed the microstructure of DF. The highest ratio of galactose contents was found in IDFs, accounting for 28.91-37.21%, while SDFs possessed the most percentage of glucose (31.95-44.61%), and E-SDF had the lowest molecular weight (20.42 kDa). SDFs exhibited different water and oil holding, cholesterol and sodium cholate adsorption capacity, amylase and lipase inhibition activities, and proliferation effect, among which F-SDF was the best. Meanwhile, correlation analysis revealed that the enzyme inhibition ability of SDF was strongly related to its loose porous structure, and the proliferation effect was closely associated with the monosaccharide types. In conclusion, biological processing could improve the functional properties and biological activities of DF better than physical processing.