Abstract
The total polyphenol contents (TPC) of leaf extracts from 116 varieties of sweet potato cultivated in China were determined by Folin-Ciocalteu method. In addition, the crude extract (CE) of Pushu 53 leaves, with relatively higher TPC and its fractions of chloroform, ethyl acetate, n-butanol and water, were prepared and subjected to the determination of TPC, evaluation of antioxidant activities in vitro by assays of DPPH, ABTS and FRAP, and analysis of phenolic constituents by high performance liquid chromatography (HPLC) and HPLC–mass spectrometry. Our results show that the extracts demonstrated potential antioxidant activity, and that a satisfactory correlation between TPC and antioxidant activity was observed. In addition, the main bioactive compounds for the antioxidant activity of the extract were polyphenols, especially derivatives of caffeoylquinic acid (CQA), such as 5-CQA, 3,4-diCQA, 3,5-diCQA, and 4,5-diCQA. Their contents (8.95%) were 0.41, 3.41, 4.09, and 1.04%, respectively, accounting for 79.6% of TPC in CE (11.24%).
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