Microwave-assisted extraction for the recovery of antioxidants from waste Equisetum arvense

Microwave-assisted extraction was optimised by the response surface methodology in order to enhance the extraction of polyphenols from Equisetum arvense (horsetail). Under the optimal conditions the total polyphenol content in extract reached a concentration of 161.57 mg of gallic acid equivalents per g of extract dry matter. The optimal conditions were reached with 54.5% of ethanol, 45.1 mL/g liquid/solid ratio, the microwave power of 170 Wand 80s extraction time. The antioxidant activity of obtained extract was evaluated by FRAP (ferric reducing antioxidant power) and DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity assay. Since, the conditions that favoured maximum polyphenol content in extract were the same as the conditions that favoured maximum antioxidant activity, the polyphenols were identified as the predominant antioxidants in horsetail extracts. When compared to the conventional extraction method (solid liquid extraction for 12 h), our results showed that more polyphenols can be extracted from waste horsetail using microwave extraction and aqueous ethanol, for just 80s. The extracts obtained by optimised extraction procedure exhibit significant antioxidant activity and can be used as a natural source of antioxidants. (C) 2014 Elsevier B.V. All rights reserved.