Optimizing Acidity and Extraction Time for Polyphenolic Recovery and Antioxidant Capacity in Grape Pomace Skin Extracts with Response Surface Methodology Approach

Objectives were to evaluate and optimize single and cumulative influences of extraction times (30, 45, 60 min) and acidity (0, 0.5, 1% of HCl) on quantities of total polyphenols (TP), hydroxycinnamic acids (HCA) and antioxidant capacity (AC) extracted from red grape skin pomace extracts (Vitis vinifera, cv. Merlot). Increasing time and acidity increased TP, HCA and AC. Highest quantities of TP, HCA and AC were at 1% HCl and between 45 and 60 min. Time had little influence on amounts of polyphenols without HCl. For most of extraction times, AC followed similar trends as studied polyphenols. AC remained constant between 30 and 45 min for low concentrations of HCl. Calculated optimal extraction conditions for: HCA = 7.93 mg/g dry pomace, t = 60 min, HCl = 0.84%; TP = 99.99 mg/g dry pomace, t = 60 min, HCl = 0.79%; DPPH = 2,055.75 mg/100g were t = 60 min and HCl = 0.77%. All variables (TP, HCA and AC) strongly increased as a function of each other. Constructed mathematical models retained these relations. Practical Applications Interest for the use of winery byproducts as a source of polyphenols in industrial production is steadily increased over the last decade. Extracted polyphenols from such materials can be successfully added to the functional foods and provide substantial economic benefits for food industry along with nutritive foods. Therefore, optimizing all possible parameters for polyphenolic recovery (such as acidity and time) from grape pomace are directly related with economic and nutritional cost-benefits of industrial processing.