Resveratrols in Vitis berry skins and leaves: their extraction and analysis by HPLC

An orthogonal L(36) (6)(5) test design was applied to select the optimum conditions for extracting resveratrols from grape berry skins and leaves. Solvent choice was the most important factor in the extraction of resveratrols, and mixed methanol and ethyl acetate [50:50 (v/v)] had much higher extraction efficiency than the other five solvents tested. For extracting resveratrols, 1g of berry skins or leaf tissue extracted in 10 mL methanol and ethyl acetate [50:50 (v/v)] for 24h at 25°C in darkness was the optimized extraction condition. The optimized analytical method for HPLC was a multi-step gradient elution using acetonitrile and water. The optimized method was used to determine resveratrols among three different cultivars. The cultivar 'Zhi 168' had the highest total resveratrols in berry skins while 'Saint-Emilion' had the lowest resveratrols. The resveratrol content of 'Beta' was between that of 'Zhi 168' and 'Saint-Emilion'.