Development of new ultrasonic–solvent assisted method for determination of trans-resveratrol from red grapes: optimization, characterization, and antioxidant activity (ORAC assay)

This work was aimed at developing an ultrasonic-assisted extraction of trans-resveratrol from red grape wastes using a new combination of solvents and response surface method- Box–Behnken design. The experiment was carried out on the industrial waste, skin, and pulp parts of 18 different types of Iranian red grapes. Ultrasound-assisted solvent extraction was carried out using different ratios of ethanol:polyethylene glycol (PEG):water (v/v), ultrasonication time, and temperature. The optimized conditions were achieved as a combination of 19.4 min, 53.6 °C, and 48:32:20 (v/v), which remarkably improved the extraction of trans-resveratrol content. The presence of PEG in the extraction medium enhanced the extraction efficiency by 39.48%. Reverse phase high performance liquid chromatography ultra-violent (RP-HPLC-UV) was applied for the quantification. The amounts of trans-resveratrol varied between 68.36 ± 3.06 and 862 ± 4.67 µg/g-dry material of the initial samples based on optimized conditions. Retention time of trans-resveratrol was obtained in less than 5 min, which indicates the high accuracy of developed HPLC method. There was a significant relationship between the amount of resveratrol and antioxidant activity. Antioxidant activity of samples extracted by optimized method was about four times higher than conventional method (80:20 ethanol:water (v/v), 30 min sonication, and 60 °C temperature) measured by oxygen radical absorbance capacity (ORAC) assay. This research provided food grade extraction method due to reduction in the use of ethanol in extraction process. Furthermore, the results can provide a new HPLC elution method for easy and fast detection and quantification of trans-resveratrol in industrial scale.