Phenolic compounds and biopotential of grape pomace extracts from Prokupac red grape variety

Phenolic compounds and biopotential (antioxidant, cellular antioxidant and cytotoxic activity) of grape pomace (GP) skin, seed, stem and whole GP originating from indigenous red grape variety Prokupac were evaluated. The UHPLC-Orbitrap MS4 analysis showed the presence of 75 phenolic compounds (57 non-anthocyanins and 18 anthocyanins), among which considerable content of ethyl gallate was observed and malvidin-3-O-hexoside-(8,8)-methylmethyne-(epi)catechin was identified. The stem had significant content of stilbenoids. The GP seed and the whole GP showed the highest antioxidant activity estimated by ABTS•+ DPPH• and H2O2 scavenging assays that were strongly correlated with the presence of flavan-3-ols, phenolic acids and ethyl gallate. The GP skin exerted cellular antioxidant activity on adenocarcinoma cells (EC50 = 56.4 mg TPCs/mL) which was strongly correlated with the presence of flavonols and anthocyanins. These by-products of Prokupac red grape variety are a notable source of phenolic compounds with good antioxidant activity that can be extensively used in food and pharmaceutical industry.