Rapid analysis of stilbenes and derivatives from downy mildew-infected grapevine leaves by liquid chromatography-atmospheric pressure photoionisation mass spectrometry.

Resveratrol, trans-epsilon-viniferin and trans-delta-viniferin are the major stilbenes induced in downy mildew infected grapevine leaves. In addition, nine minor polyphenolic compounds, described as stilbenes derivatives, have been separated and detected among known stilbenes after a methanolic microextraction of small pieces (1-2 mg) from infected grapevine leaves with a rapid, qualitative and optimized HPLC method coupled to mass spectrometry using atmospheric pressure photoionisation (APPI-MS(n)). The characterization of unknown stilbenic derivatives as six resveratrol dimers, two dimethylated resveratrol dimers and a resveratrol trimer are reported. Therefore, structures have been proposed for the dimethylated resveratrol dimers. Use of an easy sample treatment and the LC-APPI-MS(n) method results in spectral data of these minor naturally occurring viniferin analogues.

Fractionation of grape tannins and analysis by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry.

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.

Delta-viniferin, a resveratrol dehydrodimer: one of the major stilbenes synthesized by stressed grapevine leaves.

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.