EXTRACTION OF BIOACTIVE COMPOUNDS FROM GRAPE SKIN RESIDUE

Agriculture and the food industry generate agro-industrial residues, which may contain bioactive compounds like flavonoids, polyphenols, and tannins. These compounds may provide agro-industrial residues with antioxidant and antimicrobial properties, being potentially applicable in the food and bioplastic industry. The wine industry produces a large quantity of wastes and by-products such as grape pomace, grape seeds, grape stalks, and wine lees, which correspond to approximately 30% w/w of the starting grape. Grape skin contains important bioactive compounds (such as anthocyanins and phenolic compounds) with interesting applications in the area of food and biomaterials. Here, we have used Completely Randomized Design (CRD) to evaluate different green extraction treatments of bioactive compounds from grape skin. The treatments were A: mixture (85:15) of ethanol as solvent and 0.1 M hydrochloric acid (25 ºC, 2 h), B: water as solvent at 25 ºC for 2 h, C: ethanol as solvent (25 ºC, 2 h), D: water at 60 ºC for 2 h, and E: water as solvent for 4 h. The resulting extracts were characterized. °Brix was measured with a refractometer; the concentration of total anthocyanins (Cyanidin-3-Glycoside Equivalent - mg/L) was analyzed by spectrophotometry at different pH (1.0 and 4.5); total phenolic compounds (Gallic Acid Equivalent - mg/L) was determined by using Folin-Ciocalteu's reagent; titratable acid (g/100 g extract) was determined; and the dry matter content was obtained by using a forced circulation oven (105 °C, Quimis). The antioxidant activity of the extracts was determined by using DPPH• radical and is expressed as percentage. The results were statistically analyzed at 5% confidence level by ANOVA and multiple comparison Tukey’s test; Statistical 13.0 software was employed. Treatments A and D allowed similar anthocyanin (231.81 and 215.39 mg/L C3GE, respectively) and phenolic compound content to be extracted (103.17 and 97.35 mg/L GAE respectively). These treatments were the most efficient for extracting bioactive compounds from grape skin. The extracts had antioxidant activity by DPPH in the range from 85 to 95%. Meanwhile, the extract obtained with treatment D contained more dry matter than extracts from other treatments. Water as solvent was efficient for extracting bioactive compounds from grape skin. The extracts produced from skin grape by using the five treatments tested here presented significantly different Brix, titratable acid, and antioxidant activity as revealed by Tukey’s test. In conclusion, water as solvent and heating are more efficient for a green extraction of bioactive compounds with antioxidant activity from grape skin.