Mineral determination and anti-LDL oxidation activity of sweet potato (Ipomoea batatas L.) leaves

In this study, the essential minerals Fe, Ca and Mg including the essential trace elements of Cr, Co, Ni, Cu and Zn in 11 species of sweet potato (Ipomoea batatas L.) leaves were determined by ICP–MS. The levels of these elements were similar to those of common green leafy vegetables. The ratio of K and Na for the seven species of sweet potato leaves was higher than that of spinach, indicating that sweet potato leaves may be used in anti-hypertensive diet. The selenium and manganese contents were higher in all the sweet potato leaves than in other green leafy vegetables, such as spinach and water spinach. In addition, the anti-oxidative activity of the sweet potato leaves was examined in a low-density lipoprotein (LDL)-oxidation induction system. All the caffeoylquinic acid (CQA) derivatives indicated an anti-LDL oxidation activity at low concentrations (1–5 μM) and particularly, the activity of 3,4,5-triCQA was remarkably higher than those of 5-CQA and diCQA, such as 4,5-diCQA, 3,5-diCQA and 3,4-diCQA. The antioxidant activity of sweet potato leaves was correlated with the amounts of CQA derivatives in the range of r = 0.69–0.75. These results suggested that sweet potato leaves may prevent that developing atherosclerosis causes the oxidative modification of LDL. This study demonstrated that the sweet potato leaves containing an abundant nutrient mineral and functional polyphenol will be useful as a functional food material.