Grape pomace as an alternative source for the sustainable production of polyphenol-rich extracts

The increasing demand of agro-industrial products worldwide is making their by-products a serious problem affecting the global ecosystem and environment because of their accumulation and disposal. Being a rich source of polyphenols, grape pomace has already proven in our previous, recent paper, through HPLC-DAD analysis, antioxidant and antimicrobial assays, to be a precious secondary raw material to have an alternative usage to assist human health. In this follow-up work, seventeen different varieties of grape pomaces, collected from Apulia (Italy), have been used to perform the solid-liquid extractions with the previously identified best Deep Eutectic Solvents (DESs). These media represent an alternative and ecological solution to classic solvents and can be considered edible for animals and/or humans. Chemical analyses of the extracts were performed at HPLC-DAD, using the already published optimized method, to investigate the presence of fourteen selected phenolic compounds. Then, Sangiovese and Merlot grape pomaces’ varieties, extracted with Betaine/Lactic Acid (1:4 mol/mol + 40% H2O; Bet/LA) and Choline Chloride/Ascorbic Acid (2:1 mol/mol + 40% H2O; CC/AA), were selected for a further analysis at LC-QTOF-MS. The presence of sixty-two polyphenols was assessed with extracting yields around three times higher or more for Bet/LA compared to CC/AA Acid DES. Agar diffusion antimicrobial assays contributed to confirm these results showing a much less qualitative efficacy for Choline Chloride-based DES extracts, especially against pathogenic fungi. Then, in vitro digestion experiment was carried out on freeze-dried Bet/LA DES extracts both from Sangiovese and Merlot grape pomaces to deepen differences in composition and bioactivity in each studied phase. The obtained results will be discussed for a possible application of these products as food and/or feed supplements.