Polymeric proanthocyanidins from grape skins

Abstract

LC-mass spectrometric analysis of the degradation products released by thioacidolysis of a grape ( Vitis vinifera var. Merlot) skin extract showed that catechin, epicatechin, epicatechin gallate and epigallocatechin were the major constitutive units of grape skin tannins. Gallocatechin and epigallocatechin gallate were also detected. Epicatechin represented 60% of the extension units, whereas 67% of the terminal units consisted of catechin. Six fractions were prepared from the skin tannin extract by normal phase and analysed by reverse-phase HPLC after thioacidolysis. The mean degree of polymerization (mDP) calculated for each fraction ranged from three (in fraction I) to 80 (in fraction VI), confirming that proanthocyanidins were eluted from the normal phase column in increasing order of M r . All fractions contained prodelphinidins. The proportion of galloyllated units was low (3% to 6%) and independent of mDP.