Otimização da extração de polifenóis do resíduo de uva e sua estabilidade durante armazenamento

Abstract

Fruit juice processing is a sector of the food industry that produces abundant waste. Recent research has highlighted these agroindustrial residues as potential sources of bioactive phytochemicals. For this reason, the research aimed to extract polyphenols from grape residue and evaluate their stability during storage. The extractions were performed with ethanol acidified with citric acid according to the Box-Behnken design adjusted to three variables, temperature, solid/liquid ratio and time. The total anthocyanins content, total flavonols and total phenolics of the extracts were quantified and analyzed by the response surface methodology to determine their dependence on the variables under study. The multiple response optimization was performed with the desirability function to maximize the extraction. The extract obtained with the optimized parameters was concentrated, stored for 83 days at 4°C, and periodically the content of monomeric anthocyanins and the percentage of polymeric color were determined. With this data the reaction kinetics were modeled. Additionally, the physicochemical and chromatic characteristics of the concentrated optimized extract were determined. The result of the optimization of extraction showed that the temperature of 60°C, the solid:liquid ratio of 1/25 g.mL-1 and a time of 80 minutes, maximized the recovery of total anthocyanins (30.96 mg.100g-1), total flavonols (73.34 mg.100g-1) and total phenolics (856.78 mg EAG.100g-1). These conditions were determined for a global desirability (D) of 0.77. The optimized concentrate extract showed soluble solids content of 34.07 °Brix; total anthocyanins of 39.95 mg.L-1; total flavonols of 118.49 mg.L-1; total phenolics of 2,257.44 mg EAG.L-1; polymeric color of 46.63%; water activity of 0.94; pH of 2.14; and the color with luminosity (L *) of 24.32; red component (a*) of 26.32 and yellow component (b*) of 5.14. The stability study indicated that both anthocyanin degradation and polymeric color generation follow first order kinetics, with reaction rates (k) of 4.10 x 10-3 day-1 and 3.46 x 10-3 day-1, respectively. The degradation of anthocyanins by 50 %, ie the half-life (t1/2) would occur at 169 days of storage. In conclusion, ethanol acidified with citric acid can be efficiently used to extract polyphenols from grape residues, with a reasonable stability that would allow it to be stored for later use as a natural additive.