New advancements in conventional and DES-based extraction of phenolic compounds from Aglianico red grape pomace

Grape pomace is the most abundant winery waste, accounting for about 60 % of solid by-products. Despite being an environmental and economic burden, if properly treated it can be turned into a precious source of bioactive molecules. In this context, we compared the efficiency of extraction protocols based either on deep eutectic solvents (DESs) or conventional ones, with the purpose of proposing convenient procedures to recover residual phenolic compounds from Aglianico red grape pomace. The DES-based extraction protocols comprised choline chloride as a hydrogen bond acceptor and either oxalic or malic acids as hydrogen bond donors; conventional solvents were acetone and methanol. The DES-based protocols outperformed the conventional ones by far, with the mixture composed of a 1:1 molar ratio of choline chloride and oxalic acid with 25 % water (pH 1.65; at 40 degrees C) exhibiting the highest extraction yields per gram of dry grape pomace. Quali-quantitative LC-MS/MS analyses were conducted to identify specific polyphenols. Additionally, the antioxidant activity of all the extracts was measured by DPPH assay. Again, the DES-based extracts were the most active, the mixture composed of a 1.5:1 ratio of choline chloride and malic acid with 50 % water (pH 2.25; at 40 degrees C) showing the highest antioxidant properties. Finally, the outcome of the present study, once scaled up to industrial levels, is expected to benefit wineries and other food industries by diversifying their profits within a circular economy.