ASSAY OF RESVERATROL GLUCOSIDES AND ISOMERS IN WINE BY DIRECT-INJECTION HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

We have developed a normal-phase high-performance liquid chromatographic method to measure the glucosides of cis- and trans-resveratrol as well as the free isomers in commercial wines. The procedure utilises a novel technique for calibration requiring only the trans-resveratrol in pure form and the conversion of the glucosides to the free isomers by hydrolysis with beta-glucosidase. Only 20 mu l of sample is needed for direct injection without prior preparation, and isocratic elution separates the 4 compounds of interest in approximately 50 min. Calibration curves are linear, and stable for several months. Recovery was around 100% for all compounds, and replicate analyses gave coefficients of variation of 0.4-6.7%. The limits of sensitivity were 0.2 and 0.1 mu moles l(-1) for the glucosides and free isomers of cis- and trans-resveratrol, respectively. A preliminary survey of sixteen wines from eight countries or regions revealed the presence of all four compounds in fourteen; the glucosides of resveratrol were present in higher concentrations than the free isomers in five of the wines.