Extraction optimization for antioxidant phenolic compounds in red grape jam using ultrasound with a response surface methodology

Optimization of the extraction methodology for antioxidant phenolic compounds in red grape jam was performed with an ultrasound-assisted system. The antioxidant phenolic compounds were extracted and analyzed by determining the total phenolic content (Folin Ciocalteu), as well as by employing free radical DPPH and the beta-carotene/linoleic acid system. To optimize the parameters of solvent concentration, time and extraction temperature, the experiments were carried out using the central composite rotatable design (CCRD) method. Using response surface methodology (RSM), the best combinations achieved were with 60% ethanol and water for 20 min at 50 °C. The optimized parameters for this method were compared to an extraction method that has been commonly noted in the literature, which used to be the standard method, and the results were expressed in the milligram equivalent of quercetin per gram of jam (mg E.Q/g Jam). With the new method, the antioxidant potential measured by DPPH was 70% higher than that obtained with the standard extraction method, and the antioxidant potential measured using the beta-carotene/linoleic acid system was 65% higher. In addition, a significant decrease in the total analysis time was achieved (from 10 h to 30 min), when compared to the standard method.