Profiling of phenolic acids and flavonoids in sweet potato (Ipomoea batatas L.) leaves and evaluation of their anti-oxidant and hypoglycemic activities

Sweet potato (Ipomoea batatas L.) leaf phenolic acids (SPLPA) and sweet potato leaf flavonoids (SPLF) were characterized using ultra-high-performance liquid chromatography (UHPLC)-hybrid quadrupole-orbitrap mass spectrometry and UHPLC coupled with a diode array detector. The anti-oxidant and hypoglycemic activities were analyzed using 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), 1,1-diphenyl-2-picrylhydrazyl radical scavenging capacity and ferric reducing anti-oxidant powder assays, and α-glucosidase and α-amylase inhibitory assays. The mechanism of inhibition of SPLPA and SPLF against α-glucosidase was studied using kinetic analysis. Thirteen phenolic acids were identified in SPLPA, of which three di-caffeoylquinic acids (60.6%) were most prominent. Ten flavonoids were identified in SPLF and astragalin (28.1%) was the major component. Protocatechualdehyde, ethyl caffeate and quercetin were also identified, showing strong anti-oxidant capacities and inhibition of α-glucosidase and α-amylase. Kinetic analysis showed that SPLPA and SPLF both reversibly inhibited α-glucosidase, in a mixed-type manner, with IC50 values of 330 and 250 μg/mL, respectively. The results suggested the potential benefits of using sweet potato leaves.