Qualitative Analysis of Grapevine Tannins by Mass Spectrometry and their Inhibitory Effect on Stilbene Oxidase of Botrytis cinerea

Abstract

The pure tannin extracts from grape berries of Gamay and Gamaret varieties contain a mixture of proanthocyanidins and proanthocyanidin gallates. A sensitive LC-MS method has been developed for the qualitative analysis of the oligomers and polymeric fractions. The potential of ESI-IT or MALDI-TOF mass spectrometry permit us to characterize these tannins. Polymers were fractionated according to the mean degree of polymerization (mDP), using either a divinylbenzene phase or a glass powder. The mDP is obtained by thiolysis reaction and the fractions are analyzed by MS. Polymeric proanthocyanidins (PPRA) were purified from grape berries at full bloom, pea size, bunch closure, véraison and harvest, their mDP calculated and their inhibitory capacity on B. cinerea stilbene oxidase tested at 3.5 to 70 nmoles for 3 ml of enzymatic reaction volume. ED50 of PPRA concentrations was measured for each developmental stage and for both grape varieties Gamay (sensitive to grey mould) and Gamaret (resistant). The higher the mDP of PPRA fraction, the more effective is the inhibitory activity. From grape berry pea size, mDP of PPRA of Gamaret (9.53 to 11.77) were always higher than those of Gamay (7.46 to 8.74) and ED50 of Gamaret PPrA were under 5 nmoles 3ml?1 while ED50 of Gamay PPRA were at 6.5 to 7.25 nmoles 3 ml?1.