Assessment of (poly)phenols in grape (Vitis vinifera L.) stems by using food/pharma industry compatible solvents and Response Surface Methodology

A Box–Behnken design of Response Surface Methodology (RSM) was conducted to analyse the effect of time (10–30 min), temperature (25–95 °C), and solvents concentration (5–90%) on the extraction of total phenolics, flavonoids, ortho-diphenols, and anthocyanins as well as to assess the ABTS+ scavenging capacity, which were considered as response variables. Values coefficients of determination (R2), ranging from 0.903 to 0.996, fitted for describing efficient extraction of bioactive (poly)phenols and antioxidant activity. The recorded data allowed to establish the optimal extraction conditions at 23.0 min, 95.0 °C, and 57.9% of food-quality ethanol/water for Vitis vinifera L. var. ‘Viosinho’ (white variety), and 23.4 min, 84.2 °C, and 63.8% for var. ‘Touriga Nacional’ (red variety). The achievement of optimal extraction conditions of phenolics from grape stems using solvents compatible with further uses in food/pharma industries demonstrated that RSM constitutes a powerful tool for deriving optimal conditions for extraction of antioxidant phenolic compounds from grape stems.