From by-products to food ingredients through fermentation: sustainable valorization of grape pomace and brewer’s spent grains

In light of the growing demand for sustainable approaches in the food sector, this study investigated the biotechnological potential of fermentation as a strategy to valorize agro-industrial by-products, specifically brewer’s spent grains (BSG) and grape pomace (GP). Selected strains of lactic acid bacteria and yeasts, including commercial cultures and isolates from the DISTAL collection (University of Bologna), were used for the fermentation of brewer’s spent grains (BSG), whereas grape pomace (GP) was fermented using selected yeast strains only. Fermented and control samples underwent comprehensive characterization, including analyses of the fermentation process, antioxidant capacity, and total phenolic content. Their functional properties were further assessed by evaluating their effects on gastrointestinal pathogens (planktonic growth and biofilm formation), modulation of gut microflora, and viability of intestinal cell lines (Caco-2 and HT-29). Anti-inflammatory activity was also examined in both intestinal cells and RAW 264.7 macrophages by measuring nitric oxide (NO) inhibition, a key inflammatory mediator. The results demonstrated that fermentation significantly enhanced the functional properties of BSG, while the effects on GP were comparatively limited. Several strains exhibited promising functional attributes, particularly in BSG matrices; however, strain selection should ultimately be guided by the intended application, whether prioritizing antimicrobial protection, anti-inflammatory effects, or antioxidant capacity.