Delta-viniferin is a resveratrol dehydrodimer, an isomer of epsilon-viniferin. This compound has been reported as a molecule produced in vitro by the oxidative dimerization of resveratrol by plant peroxidases or fungal laccases. It was also recently identified in wines and in grape cell cultures. We have now identified this dimer by NMR, high-performance liquid chromatography-diode array detection (HPLC-DAD), and HPLC-mass spectrometry (MS) in grapevine leaves infected by Plasmopara viticola (downy mildew) or UV-C irradiated. Its concentration was higher than that of epsilon-viniferin and constitutes one of the most important phytoalexins derived from resveratrol.

Latency and development of Botrytis cinerea were assessed under field conditions and after artificial inoculation of two grape varieties, Gamay (susceptible) and Gamaret (resistant). When the percentage of latent Botrytis was the same for both varieties, severity of visible grey mould remained very low in Gamaret berries, while Gamay clusters were destroyed by the disease to a high percentage. Some biochemical parameters were measured in berries, such as constitutive and induced anti‐fungal compounds, polymeric proanthocyanidins and lipid peroxidation products as markers of senescence. Differences were observed in polymeric proanthocyanidins (PPRA) of Gamaret compared with those of Gamay. Concentration and mean degree of polymerization (mDP) of PPRA were always higher in the berries of the resistant variety. The inhibitory effect of Gamaret PPRA on enzyme activity remained until harvest whereas Gamay PPRA lost their inhibitory activity at the beginning of véraison. Based on these results, resistance to B. cinerea seems to be linked to the maintainance of the fungus in its latent form in berries, mainly due to the ability of Gamaret PPRA to inhibit macerating fungal enzyme activities.

Polymeric tannins, extracted from grape berries (Gamay variety), were fractionated according to their mean degree of polymerisation (mDP) on a styrene-divinylbenzene phase eluted with a gradient of methanol:chloroform. Increasing the percentage of methanol led to the solubilisation of higher molecular weight tannins. The mean mDP of each collected fraction was determined by acid-catalysed degradation in the presence of a nucleophilic reagent. The fractionation method produced a linear gradient of mDP varying between 1.84 and 19.34. The fractions were partially characterised by matrix assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF/MS). The spectra showed a complex mixture of proanthocyanidins and galloylated proanthocyanidins up to 4000 amu.

Tannins are highly polar, water-soluble and thermally-labile compounds which are difficult to ionize. Mass spectrometry is very useful for the structural determination of such compounds. In this article, we describe a sensitive method for the identification of tannic composition in grape berries (var. Gamaret). An ion trap, equipped with an electrospray ionization (ESI) interface, allowed us to develop multiple-stage fragmentation (MS n), which provided useful structural information. This technique was applied to a mixture of proanthocyanidins and proanthocyanidin gallate oligomers (B-type) generating identical ion sequences for each parent ion.

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.