Abstract:This study employed Lactobacillus gallinarum FB20，a β-glucosidase-producing strain，to ferment carrot pomace for the extraction of soluble dietary fiber （SDF） and insoluble dietary fiber （IDF）. The safety of both fiber types was confirmed through cell-based assays and zebrafish embryo toxicity tests. Structural and prebiotic properties were characterized by analyzing monosaccharide composition and scanning electron microscopy，alongside evaluations of probiotic growth promotion，in vitro simulated digestion，and changes in microbial composition and short-chain fatty acid （SCFA） profiles after in vitro fermentation. The results indicated that both types of dietary fibers are safe for consumption. Structural analyses revealed distinct monosaccharide compositions and microstructural features between SDF and IDF. Both fibers enhanced the growth of Lactiplantibacillus plantarum FB13，Bifidobacterium breve FB18，and Lactobacillus rhamnosus GG，with IDF demonstrating superior performance compared to SDF. During in vitro simulated digestion，neither fiber was degraded in the oral or gastric phases. In vitro fermentation results showed that，compared to the control and IDF groups，the SDF group promoted a more balanced gut microbiota composition，notably increasing the relative abundances of the benefit bacteria in the phylum of Bacteroides and Firmicutes，etc. Additionally，the concentrations of SCFAs—including butyric，acetic，hexanoic，and pentanoic acids—were significantly higher in the SDF group.