Valorization of grape pomace by microbial fermentation: Composition, biological activities and potential applications for the food industry

Grape pomace is a rich source of nutrients and bioactive substances, including dietary fiber, (poly)phenols, and other phytochemicals. This review aims to highlight the current knowledge on microbial fermentation of grape pomace, composition and biological activities of fermented grape pomace and discuss the potential of using fermented grape pomace for the development of functional food ingredients, supplemented foods, and nutraceuticals. Fermentation of grape pomace using various microorganisms, including filamentous fungi, edible mushrooms, yeast, and lactic acid bacteria, has been shown to enhance the (poly)phenolic profile of grape pomace. Furthermore, bioactive microbial metabolites (postbiotics) such as gallic acid, pyrogallol, scopoletin and catechol, which were not detected in the initial pomace-based substrates or extracts, were produced through biotransformation. Biotransformed grape pomace has exhibited beneficial and enhanced biological properties such as antioxidant, anti-inflammatory, anti-cancer, and anti-steatotic activities. Microbial-based valorization of grape pomace offers a sustainable approach to producing novel food ingredients and nutraceuticals with valuable health benefits.