Extraction of caffeoylquinic acids (CQAs) from sweet potato leaves and stems

Sweet potato, Ipomoea batatas, is a widely cultivated vegetable and important food source. The leaves and stems of sweet potato contain polyphenolic natural products called caffeoylquinic acids (CQAs), which exhibit a variety of biological activities, including inhibition of amyloid peptide aggregation. Utilizing revised-phase HPLC, quantitative analysis of 3,4-, 3,5-, and 4,5-diCQA in sweet potato leaves and stems extracted under different solvent and temperature conditions. The total amount of polyphenols was also determined using the Folin-Ciocalteu method. The followings were found: (1) leaves and stems collected in spring contain more CQAs/polyphenols than leaves and stems collected in autumn; (2) roasting the leaves and stems does not affect the amounts of CQAs/polyphenols; (3) extraction in H₂O at 90 °C provides better yield of CQAs than extraction in H₂O at 5 °C. The results of the present study suggest that drinking hot H₂O extracts of sweet potato leaves and stems as a tea is a useful way to obtain CQAs/polyphenols as a healthy vegetable food material.