Determination of trans-resveratrol in grapes by pressurised liquid extraction and fast high-performance liquid chromatography

A study has been made of the extraction of trans-resveratrol from grapes using pressurised liquids (PLE); for this, the first stage was to determine the stability of this compound during extractions at different temperatures (50, 100, 150 °C), with quantitative recoveries being obtained up to 150 °C. By employing solid-phase extraction (SPE) it was possible to retain this compound and separate it from other interfering substances present in the grape. The method developed comprises a sequential extraction of the sample adsorbed (0.5 g) on a polystyrene-divinylbenzene based sorbent in the extraction chamber, first with water at 40 °C and 40 atm of pressure (three cycles of 5 min), and then with methanol at 150 °C and 40 atm (three cycles of 5 min). The trans-resveratrol content of the methanolic extract is determined by means of liquid chromatography. A rapid (5 min) chromatographic method employing a monolithic column, with fluorescence detection, has been developed; for this, the conditions for detection of the compound were optimised (excitation at 310 nm and emission at 403 nm). The analytical parameters of the method of chromatographic analysis developed have been calculated: linear range (0.11–2.75 mg/L), detection limit (0.003 mg/L), quantification limit (0.004 mg/L). Using this method, three varieties of grape have been analysed and the concentration of trans-resveratrol in these has been determined.