Effects of Soluble and Insoluble Dietary Fiber from Shatianyu Pulp on Gut Microbiota

The effects of soluble and insoluble dietary fiber (DF) from Shatianyu (Citrus grandis L. Osbeck) pulp on gut microbiota were explored, so as to enrich the theoretical basis of fruits and vegetables DF in regulating gut microbiota, therefore guiding their precision nutrition processing.

In vitro fecal microbiota fermentation model was used to ferment soluble DF (SDF), insoluble DF (IDF) and total DF (TDF, IDF and SDF mixed according to their proportion in Shatianyu) for 24 h, respectively. The content of SCFAs in each fermentation broth was analyzed by gas chromatography. The structure of fecal microbiota in each fermentation group was analyzed by 16S rRNA sequencing. Microstructure of Shatianyu DF and their microbial attachment status were analyzed by scanning electron microscopy. Pearson correlation analysis was used to analyze the correlation among the relative abundance of bacteria and SCFAs content in fermentation broth.

IDF, SDF and TDF in Shatianyu pulp all improved acetic and propionic acid content in fermentation broth. IDF and TDF group showed higher acetic and propionic acid content than those in SDF group, and IDF also improved butyric acid content. After 24 h-fermentation, IDF and TDF group showed similar microbial community composition on the OTU level, which was obviously different from those of SDF group. Many rod-shaped bacteria gathering in the cracks on SDF surface were observed, however, a large number of spherical or ellipsoidal bacteria gathering in the cracks and folds on IDF surface were found. LEfSe analysis revealed that SDF specifically induced the enrichment of Veillonellaceae, unclassified_k__norank_d__Bacteria and Butyricicoccus, while IDF specifically induced the blooming of Streptococcus, Faecalibacterium, Paraprevotella, Lachnospira, and TDF specifically induced the enri-chment of Prevotella, unclassified_p__Firmicutes, Lactobacillus and Turicibacter. Furthermore, the abundance of characteristic microbes in IDF and TDF group was significantly positively correlated with SCFAs content in fermentation broth.

It was different from the traditional view that IDF mainly played a role in promoting intestinal motility, and Shatianyu pulp IDF was also an important energy source of gut microbiota, which was more effective in regulating gut microbiota producing SCFAs than those of SDF. Thus, Shatianyu pulp IDF was a potential functional ingredient of healthy food for improving intestinal microecology.