Optimisation of microwave-assisted extraction parameters for antioxidants from waste Achillea millefolium dust

Microwave-assisted extraction of polyphenols and flavonoids from waste Achillea millefolium (yarrow) dust was optimised using the response surface methodology. The influence of the extraction time (13-47 s), ethanol concentration (53-87%), liquid/solid ratio (13-47 mL/g) and microwave power (170 and 340W) was studied. The optimised conditions for the maximal recovery of polyphenols and flavonoids were as follows: 33 s of extraction time, 70% of ethanol concentration, 40 mL/g of liquid/solid ratio and 170W of microwave power. Under the optimal conditions, 237.74 +/- 2.08 mg of gallic acid equivalents per g of extract dry matter of total polyphenols, and 42.95 +/- 1.32 mg of quercetin equivalents per g of extract dry matter of total flavonoids were extracted. The optimal extract strongly reduced the diphenylpicrylhydrazyl radical (IC50 7.89 mu g/mL). The antioxidant activity of the obtained extracts was in correlation to the total polyphenol content in yarrow extracts. Compared to the conventional extractions (solid-liquid extraction (24 h) and maceration (48 h)) microwave-assisted extraction yielded extracts with higher polyphenol and flavonoid content and higher antioxidant activity in very short time (33 s). (C) 2015 Elsevier B.V. All rights reserved.