Polyphenolic composition and antimicrobial activity of extracts obtained from grape processing by-products: Between green biotechnology and nutraceutical

Vitis vinifera (grape) is a multiuse crop rich in biomolecules with recognized health-promoting effects. In the wine-making industry, pomace is the main by-product, representing up to 20% of the whole biomass. However, the pomace and juice deriving from the pressing may represent innovative raw materials, and in the present study, the aim was to compare phenolic composition and biological activities of hydroalcoholic extracts obtained from grape pomace and juice of the cultivars Sagrantino, Tintilia, Vernaccia and Falanghina. While the Falanghina hydroalcoholic extract showed the highest total phenol level and antiradical potential, in Sagrantino pomace and Vernaccia juice, the catechin concentration was up to 20-fold higher compared to the other extracts. They also displayed the highest antimycotic effects, especially against Trichophyton rubrum and Arthroderma crocatum. However, their mycostatic effects could be only partially related to the catechin content. Indeed, the putative binding of catechin towards lanosterol-14-α-demethylase, deeply involved in fungal metabolism, would occur at a concentration ten-fold higher compared to the catechin level corresponding to the extracts’ MIC; thus suggesting multiple antimycotic mechanisms. Overall, the present study suggests the valorization of grape by-products that could open new applicative scenarios in the local productive chain, often characterized by high quality wine with low productive yield.