Antioxidant and antidiabetic activities of various solvent extracts from Stachys sieboldii Miq

This study investigated the antioxidant and antidiabetic activities of Stachys sieboldii Miq. extracts by solvents (water, ethanol, butanol, chloroform, and hexane). The contents of total polyphenols (7.18-37.25 mg/g) and flavonoids (0.21-5.21 mg/g) in extracts from Stachys sieboldii Miq. showed a significant difference dependent on the extraction solvents, butanol > ethanol > water > chloroform > hexane. Antioxidant activities by DPPH and ABTS radical scavenging were increased in a dose-dependent manner. These activity trends associated with the extraction solvent were different at each concentration, but resembled phenolic compound contents trend, generally. FRAP value increased in a dose-dependent manner, but there was a difference in radical scavenging activities when comparing between extraction solvents by butanol > ethanol > hexane > chloroform > water on all concentrations. The trend of α-amylase inhibition of extracts from 1,000 μg/mL to 2,000 μg/mL was not affected as enzyme activity is promoted and not inhibited. The inhibition of α-glucosidase was increased in a dose-dependent manner without water extracts, the activity on hexane extracts was higher than others per the extraction solvent. α-Glucosidase inhibition of hexane extracts showed 57.76% at 250 μg/mL, which is 2.8 times higher than the second highest chloroform extract (20.65%). From these results, we presume that the active ingredients of Stachys sieboldii Miq. is different according to the extraction solvent and also the activity is different by these major functional groups.