In vitro fermentation behaviour of yeast β-glucans with different solubilities and molecular weights using broiler...

Yeast β-glucan, a glucose-based homopolysaccharide, is believed to exert beneficial effects in broilers by serving as a prebiotic. However, how key physicochemical properties, particularly water solubility and molecular weight (MW), influence its prebiotic efficacy remains unclear. It was hypothesised that variation in these properties would differentially alter fermentation kinetics, metabolite production, and microbial community composition. This was evaluated using an in vitro fermentation model with broiler caecal contents. Three high-purity (86.0%-94.9%) yeast β-glucans were investigated, including a water-soluble, low-MW β-glucan (SLG; ∼1-100 kDa) and two water-insoluble β-glucans with medium (IMG; mainly 10-800 kDa) and high MWs (IHG; predominantly >20 kDa, with a large fraction >800 kDa). By 12 h of fermentation, SLG-supplemented group exhibited faster gas production than IMG- and IHG-supplemented groups, accompanied by higher microbial metabolite concentrations, which were closely associated with concurrent shifts in microbial composition, particularly the enrichment of Erysipelatoclostridium and DTU089. These changes were accompanied by a reduced abundance of the Lachnospiraceae NK4A136 group and Lactobacillus pontis, along with a suppression of amino acid fermentation. In line with these patterns, SLG resulted in lower microbial diversity than insoluble β-glucans. In contrast, after 12 h, insoluble β-glucans showed sustained fermentation with increased gas, acetate, and butyrate production, accompanied by succinate accumulation for IHG and elevated propionate for IMG, with limited differences attributable to MW. These findings reveal that solubility is a key determinant of in vitro fermentation dynamics of yeast β-glucan, selectively shaping microbial community composition, including taxa such as Erysipelatoclostridium, and associated metabolite production.