Apple Pomace Fermented with Non-Saccharomyces Yeast as a Factor Modulating Gut Microbiota

The valorisation of agro-industrial by-products through fermentation offers an opportunity to develop functional ingredients with targeted effects on gut microbiota. This study evaluates the impact of apple pomace fermented at a low temperature (15 °C) by cold-adapted yeast on the structure and metabolic activity of human gut microbiota, simulated using the Simulator of the Human Intestinal Microbial Ecosystem (SHIME^®). The fermented apple pomace preparation was characterised by high stability under gastrointestinal conditions, supporting its potential applicability as a functional food ingredient. Supplementation with fermented apple pomace induced distinct changes in the composition and activity of gut microbiota compared to the non-fermented substrate, including increased abundance of the genera Akkermansia, Coriobacteriaceae, and Parabacteroides, and reduced abundance of Bifidobacterium, Klebsiella, Serratia, and Raoultella. The fermented preparation was associated with reduced accumulation of metabolites typically linked to proteolytic fermentation and a more stable metabolic profile throughout the supplementation and washout phases. Short-chain fatty acid analysis indicated that fermentation influenced both the quantity and proportional balance of microbial fermentation products, promoting profiles closer to physiological reference ranges. Overall, fermentation of apple pomace at 15 °C enhanced its functional properties and modulated gut microbiota metabolism in a manner consistent with improved ecosystem stability. These findings highlight the potential of fermented fruit by-products as sustainable ingredients for dietary strategies aiming to support gut microbial functionality.