Flavonoid Composition and Gut Homeostasis-Modulatory Effects of Shatianyu (Citrus grandis L. Osbeck) Whole Fruit Fermented by Lactobacillus rhamnosus

This study aimed to elucidate the differences in flavonoid composition and gut homeostasis-regulating effects of Shatianyu (Citrus grandis L. Osbeck) whole fruit before and after debittering by Lactobacillus rhamnosus fermentation, thereby providing the theoretical foundation for the precise nutritional processing of Shatianyu.

Shatianyu whole fruit powder (SWFP) and Lactobacillus rhamnosus-fermented Shatianyu whole fruit powder (F-SWFP) were used as test materials. High-performance liquid chromatography (HPLC) was adopted to analyze the differences in flavonoid composition and content between the above-mentioned fruit powder. Subsequently, SWFP and F-SWFP were subjected to in vitro fecal microbiota fermentation for 24 h, respectively. Gas chromatography (GC) and a lipopolysaccharide (LPS) enzyme-linked immunosorbent assay (ELISA) kit were employed to determine the content of short-chain fatty acids (SCFAs) and LPS in each fermentation system, respectively. 16S rRNA sequencing was adopted to determine the structure of fecal microbiota. The correlation between the relative abundance of fecal microbiota among SCFAs and LPS contents was revealed by Pearson correlation analysis.

Eight monomeric flavonoids, namely neoeriocitrin, naringin, melitidin, cigranoside B, cigranoside A, cigranoside C, rhoifolin, and hesperidin, were detected in both SWFP and F-SWFP. Naringin, melitidin, and cigranoside B were the major flavonoid components, accounting for approximately 85% of the total content of detected flavonoids. Fermentation with Lactobacillus rhamnosus significantly reduced the total flavonoid content in SWFP, cigranoside B, neoeriocitrin, rhoifolin, hesperidin and melitidin were the main degraded flavonoids in F-SWFP, with the degradation rates ranging from 28.1% to 78.5%. After 24 h-fecal microbiota fermentation, both SWFP and F-SWFP significantly reduced the relative abundance ratio of Bacillota to Bacteroidota in fecal microbiota, with F-SWFP exhibiting a more pronounced effect. SWFP specifically induced the proliferation of Bifidobacterium and Mediterraneibacter, whereas F-SWFP not only specifically promoted the proliferation of Segatella and g_norank_f_Prevotellaceae, but also inhibited the growth of Collinsella, Blautia, Parabacteroides, and Dialister. 24 h-fecal microbiota fermentation of SWFP or F-SWFP all significantly increased acetic, propionic, and butyric acid content but reduced LPS content in the fermentation system. Notably, F-SWFP fermentation group showed higher SCFAs but lower LPS content than those of SWFP fermentation group, also, the butyric acid and LPS content in F-SWFP group was 1.2 and 0.7 times those of SWFP group, respectively. Correlation analysis revealed that the characteristic microbes in SWFP group were significantly positively correlated with SCFAs content, whereas those in F-SWFP group were not only positively correlated with SCFAs content, but also negatively correlated with LPS content.

Compared with SWFP, F-SWFP showed a lower total flavonoid content, but exhibited greater efficacy in promoting butyrate production while inhibiting LPS production by fecal microbiota. Given the key roles of butyrate and LPS in obesity-related metabolic diseases, F-SWFP serves as a functional ingredient for ameliorating obesity-related metabolic diseases and is suitable for use in the development of healthy foods.