Optimisation of antioxidant activity of grape cane extracts using response surface methodology

Solid–liquid extraction and response surface methodology were used to optimise conditions for the antioxidant activity of grape cane extracts. The independent processing variables were ethanol concentration, temperature and solvent to solid ratio. Ethanol concentration and temperature significantly affected antioxidant activity measured by the Trolox equivalent antioxidant capacity (TEAC) assay and the oxygen radical absorbance capacity using fluorescein (ORACFL) method (p ⩽ 0.01), whereas the solvent to solid ratio did not significantly affect the activity (p > 0.05). Antioxidant activity of the extracts, determined by the TEAC assay, varied from 85.6 to 238.6 μmol Trolox equivalents/g of dry sample. ORACFL values ranged from 308.4 to 1302.7 μmol Trolox equivalents/g of dry sample. Ethanol concentrations of 40.4% and 55.4% were optimal for the highest antioxidant activities measured by the TEAC assay and the ORACFL method, respectively. The optimal temperature was 83.6 °C. Antioxidant activity correlates with total phenolic content of extracts.