Effects of extraction time, temperature and solvent on concentration and antioxidant activity of grape marc phenolics

This study was aimed to optimize the extraction of phenolic compounds from grape marc investigating extraction kinetics (from 1 to 24 h) at 45 and 60 °C, and the effect of solvent (ethanol with different water content) on phenols yield and quality of extracts (phenols concentration and antioxidant power). Extraction was a slow process, with higher yields at 60 °C than at 45 °C, and with apparent thermal degradation of constituents beyond 20 h. Phenols yield increased for water content of ethanol from 10% to 30% and remained constant for water content from 30% to 60%, while phenols concentration of extracts decreased for water content above 50%. Antioxidant power (ABTS test) highly correlated to total phenols concentration, and was not influenced by water content of ethanol, suggesting that this variable influenced only the amount but not the nature of the extracted compounds. Freeze-drying did not alter composition and antioxidant property of extracts.