Analysis of trans-resveratrol: Comparison of methods and contents in Muscatel fortified wines from Setúbal region in Portugal

Liquid chromatography and mass spectrometry conditions were developed in order to identify trans-resveratrol in sweet fortified Muscatel wines from Setúbal region (Portugal). Diode array, fluorescence and electrochemical detectors were used for quantitation purposes. The detection and quantitation limits for each detection mode were: 0.02 and 0.06 mg L−1 for UV–vis, 0.01 and 0.03 mg L−1 for fluorescence and 0.45 and 1.35 mg L−1 for electrochemical. Repeatibility (n=6) expressed as the relative standard deviation of peak areas for a standard solution of trans-resveratrol (1.75 mg L−1) was 0.5% for fluorescence and 1.5% for UV–vis and electrochemical detection modes. Samples collected at one representative producer, during the winemaking process, were injected without pre-treatment and the quantitation of trans-resveratrol was carried out using fluorimetric detection. The trans-resveratrol content decreased slightly along the winemaking process and the concentrations ranged from 0.22±0.02 to 0.16±0.02 mg L−1.After maturation stages, trans-resveratrol contents in wines collected at different producers were compared: values obtained range from 0.13±0.02 to 0.38±0.03 mg L−1. The trans-resveratrol contents in commercially available wines from the same producers were lower.