Antioxidant activities and polyphenols of sweet potato (Ipomoea batatas L.) leaves extracted with solvents of various polarities

Sweet potato (Ipomoea batatas L.) leaves are under utilized vegetables with abundant polyphenols. In this study, ten different solvents, including water, aqueous methanol, aqueous ethanol and aqueous acetone were used to investigate the effect of solvents on the recovery and antioxidant activities of polyphenols from sweet potato leaves. Results indicated that the total phenolic content in extracts ranged from 23.3 to 43.8 mg CAE/g DM, and 70% ethanol extract had the highest total flavonoid (3.4 mg QE/g DM) and total anthocyanin (36.5 mg c-3-gE/100 g DM) content. While, 50% acetone extract exhibited the highest crude extract yield (33.4% in dry materials), total phenolic content (43.8 mg CAE/g DM), as well as the strongest in vitro antioxidant activities. The best correlation with antioxidant activities was observed on total phenolics. Totally 14 phenolics were identified or tentatively identified in 50% acetone extract, caffeoylquinic acid (CQA) and quercetin derivatives were indicated as the most abundant phenolics. HPLC analysis also revealed that the extraction efficiency of 3-CQA, caffeic acid, 3,4-, 3,5- and 4,5-diCQA varied with the polarity of tested solvent, and 70% acetone showed the highest extraction capacity for 3,4-, 3,5 and 4,5-diCQA. All these data demonstrated that the types of extracting solvents impact the recovery and antioxidant activities of sweet potato leaf polyphenols greatly, and 50% (v/v) acetone is quite an efficient solvent to recover polyphenols and antioxidants from sweet potato leaves. (C) 2016 Elsevier Ltd. All rights reserved.