Simplified process of extraction of polyphenols from agroindustrial grape waste

Abstract The extraction, and stability of polyphenols from the grape residue were studied. The extractions were performed following the Box-Behnken design, and the surface response methodology was used to model the extraction of total anthocyanins (TA), flavonols (TF), and phenolics (TP). The extraction was optimized simultaneously by the desirability function. The degradation kinetics of monomeric anthocyanins, and the increase in polymeric color were modeled under refrigeration conditions. The extraction with a temperature of 60 °C, solid:liquid ratio of 1/25 g/mL, and time of 80 min, maximized the recovery of TA (30.96 mg/100 g), TF (73.34 mg/100 g), and TP (856.78 mg EAG/100 g). The degradation of monomeric anthocyanins, and the increase in polymeric color followed a kinetic first-order reaction, with reaction rates (k) of 4.10 x 10-3 days-1, and 3.46 x 10-3 days-1, respectively. The half-life (t1/2) of anthocyanins was 169 days. The ethanol-citric acid solution allowed polyphenols to be efficiently extracted from the grape residue, and had a positive effect on the stability of anthocyanins.