Barley extrudates modulate the gut microbiome–metabolome axis in vitro through β-glucan fermentation and polyphenol biotransformation

Abstract

Barley is rich in fermentable dietary fiber and phenolic compounds, both of which have recognized benefits for gut health and whose functionality is influenced by processing. Here, four barley genotypes differing in β-glucan content, type of starch, and phenolic profiles were extruded to obtain ready-to-eat products, which were then evaluated using a combined in vitro digestion–colonic fermentation model. The gastrointestinal fate of β-glucans and phenolics, short-chain fatty acids production, phenolic metabolite formation, and gut microbiota composition were assessed. After digestion, substantial amounts of β-glucans and phenolics remained in the non-bioaccessible fraction, supporting their relevance as substrates for colonic fermentation. During fermentation, the β-glucan-rich genotypes Annapurna® and Hilose® showed the strongest butyrogenic response, while the purple-grain genotype DHL-151340, characterized by a flavone- and anthocyanin-rich profile, showed an earlier and more pronounced accumulation of low-molecular-weight phenolic catabolites. Compared with the control, barley extrudates induced time-dependent shifts in microbiota composition, although community profiles tended to converge at later fermentation stages. Overall, genotype- and processing-driven differences translated into distinct fermentation and phenolic biotransformation footprints, highlighting the relevance of barley matrix composition in shaping the colonic fate of cereal bioactive compounds.