Rapid Extraction of Polyphenols from Red Grapes

Abstract

Assessment of the phenolic content of red grapes is an important prerequisite for understanding how grape phenols impact wine quality. The influence of selected factors on extraction efficiency of phenols from eight different red grape cultivars was investigated to determine a rapid and robust extraction method. The effects of solvent contact time, extraction temperature, and concentration of ethanol and hydrochloric acid on extraction of total phenols and anthocyanins were investigated in a series of statistically designed factorial experiments. The results were compared to the “total” concentrations as measured by a modified “total” extraction protocol and the data were expressed as relative extraction efficiencies. Both extraction temperature and concentration of the solvents ethanol and hydrochloric acid exerted highly significant effects on the extraction of both total phenols and anthocyanins. The optimized extraction procedure was as follows: mix 50% v/v acidified aqueous ethanol (0.1 M HCl) in a 1:1 v/w ratio with crushed grapes to give a final ethanol of ∼25% v/v for 5 min at 40°C, followed by neutralization and clarification. By this rapid procedure, it was possible to extract an average 81.8% of the total phenols and 91.5% of the anthocyanins from the grapes.