Grape pomace is a potential source of natural antioxidant and antimicrobial agents. Phenolic compounds, antioxidant, and antibacterial properties of pomace extracts from four Virginia-grown grape varieties were investigated. White grape pomaces had higher (P < 0.05) solvent extraction yield than red varieties. Concentrations of total phenolic (TPC), total flavonoid (TFC), total anthocyanin (TAC), tannins, condensed tannins (CT), as well as antioxidant capacities (DPPH• and ABTS•+free radical scavenging) differed (P < 0.05) among four pomace extracts. ABTS•+ scavenging capacity was positively correlated with TPC, TFC, tannins, and CT (P < 0.05), whereas DPPH• capacity was positively correlated with TAC (P < 0.05). Nine flavonoid compounds were identified, of which catechin and epicatechin were the two most abundant. Antibacterial activity was observed against Listeria monocytogenes ATCC 7644 and Staphylococcus aureus ATCC 29213, but not against Escherichia coli O157:H7 ATCC 3510 and Salmonella typhimurium ATCC 14028. L. monocytogenes was more susceptible than S. aureus.
Keywords: Antibacterial; antioxidant; extract; grape pomace; phenolic compounds; variety.