Different microbiota modulation and metabolites generation of five dietary glycans during in vitro gut fermentation are determined by their monosaccharide profiles

Dietary oligo- and polysaccharides modulate gut microbiota and thus exert prebiotic activity, which is determined by their heterogeneous structure. To explore the correlations between monosaccharide profile and microbial community, simulated gut fermentation of different glycans, including arabinan (ArB), galactooligosaccharide (GOS), arabinogalactan (ArG), rhamnogalacturonan (RhG), and xyloglucan (XyG) that are characterized by typical sugar residues were performed. Results showed that RhG displayed high contents of galacturonic acid (344.79 mg/g), rhamnose (171.70 mg/g), and galactose (151.77 mg/g), and the degradation ratio of them after fermentation was 73.87 %, 84.96 %, and 87.11 %, respectively. Meanwhile, the relative abundance of glycan-degrading bacteria Bacteroides in the RhG was boosted from 4 h (4.97 %) to 48 h (36.45 %). Butyrate-generating bacteria Megasphaera (56.69 %) and Bifidobacterium (28.02 %) are dominant genera in the ArB, which generated the highest concentration of carbohydrate-metabolite (94.58 mmol/L) in terms of acetate, propionate, butyrate and valerate, followed by the ArG (87.36 mmol/L). However, ammonia generation of the ArG increased rapidly, representing the highest content of protein-metabolite (66.36 mmol/L) including ammonia, isobutyrate, and isovalerate. As compared, metabolites generated from protein and carbohydrates grow steadily at a low level during the XyG fermentation. Correlation analysis further indicated that Bacteroides was positively correlated with propionate (p < 0.001), galacturonic acid (p < 0.001), and rhamnose (p < 0.05), while Bifidobacterium has positive correlation with butyrate and arabinose (p < 0.01). Overall, monosaccharides composition in the different oligo- and polysaccharides induces distinct responses of the dominant microbiota and thus modulates the subsequent fermentation metabolites of carbohydrate and protein, promoting a deep understanding of the structure-fermentation relationship of dietary glycans.