Ethanol influenced fast microwave-assisted extraction for natural antioxidants obtaining from spent filter coffee

Ethanol influenced microwave-assisted extraction was performed for obtaining of natural antioxidants from spent filter coffee. The process included response surface methodology which represented the significance of both investigated variables (ethanol concentration and time of microwave radiation) on all tested responses (extraction yield, total polyphenol content (TPC), DPPH radical inhibition activity and ferric reducing ability, FRAP). The highest TPC of 398.95 mg GAE/g of extract dry matter was obtained with 20% aqueous ethanol solution under just 40 s of microwave radiation (80 W), which implies that method was very effective and thereby saved time and chemicals. Obtained extracts showed great antioxidant activities in vitro. Even 20 mu g/mL of working extract concentration inhibited 90.47% of DPPH radicals. The results suggest that examined method provides fast obtaining of high values of bioactive compounds and also ensures their biological stability. (C) 2013 Elsevier B.V. All rights reserved.