Makgeolli Lees as a Novel Prebiotic Candidate: Effects on Human Gut Microbiota and Metabolites

Makgeolli lees (ML), an underutilized byproduct of traditional Korean rice wine production, contains abundant indigestible carbohydrates and microbial residues. This study evaluates the prebiotic potential of ML using a simulated human digestion and in vitro fecal fermentation model. In vitro digestion showed that 61.30% of total carbohydrates and 89.92% of crude protein remained undigested. During in vitro fecal fermentation, treatment with ML induced compositional changes in the gut microbiota, including increased abundances of Bifidobacterium bifidum (Δ 0.37 ± 0.09%), Prevotella copri (Δ 0.98 ± 0.24%), and Bacteroides uniformis (Δ 0.46 ± 0.06%), along with a decrease in Bacteroides ovatus (Δ -2.14 ± 1.51%). In addition, SCFA concentrations were elevated after 12 h of fermentation, with acetate at 84.80 ± 4.88 mM, propionate at 43.75 ± 2.74 mM, and butyrate at 20.22 ± 0.71mM. The alterations in microbial composition and associated metabolite profiles were comparable to those observed following fructooligosaccharides (FOS) supplementation. These findings indicate that ML function as a fermentable substrate that selectively enriches health-associated gut microbiota and enhances the production of beneficial microbial metabolites, thereby supporting their potential application as a sustainable and cost-effective prebiotic candidate in dietary applications.