Antioxidant content and activity in leaves and petioles of six sweet potato (Ipomoea batatas L.) and antioxidant properties of blanched leaves

This study was conducted to compare antioxidant contents and antioxidative activities in the leaves and petioles of six sweet potato varieties, namely Danjami, Hayanmi, Hogammi, Jinyulmi, Poongwonmi, and Yeonjami. Total amount of phenolic acids was highest in Poongwonmi and lowest in Hogammi, while vitamin C level was highest in Danjami. Of four phenolic acids quantified, 3,5-dicaffeoylquinic acid was the most abundant in all varieties. The contents of phenolic acids and vitamin C were more than ten-fold higher in the leaves compared with the petioles. In addition, the leaves had much lower EC50 values for DPPH scavenging activities and reducing power than the petioles, indicating that sweet potato leaves have a higher antioxidant capacity than the petioles. Blanching, including conventional and microwave, resulted in a considerable decrease of antioxidant content and activity in the leaves due to thermal degradation and leaching.