Effects of different cooking methods on dietary polyphenol contents and the bioavailability of Ipomoea batatas Linn leaves

The aim of this study was to evaluate the dietary polyphenol contents, absorption, and bioavailability in humans after the consumption of leaves of Ipomoea batatas, also called red sweet potato leaves, cooked using two different methods. Leaves of Ipomoea batatas were subjected to typical domestic processing, including stir-fry and boiling. The impacts of these processes on the polyphenol contents were assessed. Sixteen healthy adults were enrolled in this study and were asked to ingest 200 g of boiled or fried leaves of Ipomoea batatas. Blood samples were taken for polyphenol analysis before, and 1, 2, 4, 8, 12, and 24 h after ingestion. Urine and feces samples were collected at 24-hour and 72-hour time points to evaluate the bioavailability of polyphenol. The results indicated that the stir-fry and boiling methods led to 17.02% and 22.74% losses of polyphenols, respectively. Plasma levels of polyphenols increased at 1-2 and 8-24 h after the ingestion of boiled leaves of Ipomoea batatas, and increased 4 h after ingestion of stir-fried leaves. Urinary polyphenol contents of subjects did not significantly change after ingestion of either test meal. However, the apparent absorption of polyphenols of leaves of Ipomoea batatas with the stir-fry method was 35.98% higher than the 31.03% with the boiling method. In conclusion, the stir-fry method resulted in a lower loss of polyphenols and a higher bioavailability of polyphenols from leaves of Ipomoea batatas compared to the boiling method.