The Progressive Utilization of Ponkan Peel Residue for Regulating Human Gut Microbiota through Sequential Extraction and Modification of Its Dietary Fibers

Abstract

As a by-product of citrus processing, ponkan (Citrus reticulata Blanco, cv. Ponkan) peel residue is a source of high quality dietary fiber (DF). To make a full utilization of this resource and give a better understanding on the probiotic function of its DF, soluble dietary fiber (SDF) and insoluble dietary fiber (IDF) were extracted from ponkan peel residue (after flavonoids were extracted) using an alkaline method, followed by modifications using a composite physical-enzymatic treatment. The in vitro fermentation properties of the modified SDF and IDF (namely, MSDF and MIDF) and their effects on short-chain fatty acids (SCFA) production and changes in the composition of human gut microbiota were investigated. Results showed that MSDF and MIDF both significantly lowered the pH value and enhanced total SCFA content in the broths after fermented for 24 h by fecal inocula (p < 0.05) with better effects found in MSDF. Both MSDF and MIDF significantly reduced the diversity, with more in the latter than the former, and influenced the composition of human gut microbiota, especially increasing the relative abundance of Bacteroidetes and decreasing the ratio of Firmicutes to Bacteroidetes (F/B) value. The more influential microbiota by MSDF were g-Collinsella, p-Actinobacteria and g-Dialister, while those by MIDF were f-Veillonellaceae, c-Negativicutes and f-Prevotellacese. These results suggested that the modified ponkan peel residue DF can be utilized by specific bacteria in the human gut as a good source of fermentable fiber, providing a basis for the exploitation of the citrus by-product.

Keywords: dietary fiber; gut microbiota; microbial diversity; physical-enzymatic modification; ponkan peel residue; short-chain fatty acids.

Figure 1

Changes in pH during in vitro fermentation of ponkan peel residue MDF. Different lowercase letters on value curves of groups at each sampling time represent significance at p < 0.05. CK, blank control; AC, positive control; MSDF, modified soluble dietary fiber; MIDF, modified insoluble dietary fiber.

Figure 2

Changes in SCFA contents after in vitro fermentation of ponkan peel residue modified dietary fibers. Different lowercase letters on the tops of columns in each chart indicate significance in data among groups at p < 0.05. CK, blank control; AC, positive control; MSDF, modified soluble dietary fiber; MIDF, modified insoluble dietary fiber.

Figure 3

Changes in the alpha diversity of intestinal microorganisms after in vitro fermentation with ponkan peel residue MDF. (a) Chao index; (b) Ace index; (c) Shannon index; (d) Simpson index. Different lowercase letters on the tops of columns in each chart indicate significance in data among groups at p < 0.05. CK, blank control; AC, positive control; MSDF, modified soluble dietary fiber; MIDF, modified insoluble dietary fiber.

Figure 4

Plots of PCoA (a) and NMDS (b) analyses on gut microbes among in vitro fermentation broths of different samples. CK, blank control; AC, positive control; MSDF, modified soluble dietary fiber; MIDF, modified insoluble dietary fiber.

Figure 5

Composition difference of the gut microbiota at phylum (a) and genus (b) taxonomic level among in vitro fermentation broths of different samples. CK, blank control; AC, positive control; MSDF, modified soluble dietary fiber; MIDF, modified insoluble dietary fiber.

Figure 5

Composition difference of the gut microbiota at phylum (a) and genus (b) taxonomic level among in vitro fermentation broths of different samples. CK, blank control; AC, positive control; MSDF, modified soluble dietary fiber; MIDF, modified insoluble dietary fiber.

Figure 6

Plots of LEfSe (a) and LDA (b) analysis on gut microbiota among in vitro fermentation broths of different samples. CK, blank control; AC, positive control; MSDF, modified soluble dietary fiber; MIDF, modified insoluble dietary fiber.

Figure 6

Plots of LEfSe (a) and LDA (b) analysis on gut microbiota among in vitro fermentation broths of different samples. CK, blank control; AC, positive control; MSDF, modified soluble dietary fiber; MIDF, modified insoluble dietary fiber.