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The methanolic extracts of 18 tropical and subtropical plants were evaluated using various in vitro assays: DPPH radical scavenging activity, H2O2 radical scavenging activity, β-carotene bleaching assay, and reducing power assay. Total phenol content measurements of several tropical and subtropical plants were determinedby Folin-Ciocalteau reagent equivalent to gallic acid and quercetin. The α-glucosidase inhibitory assay was conducted against α-glucosidase from Saccharomycescerevisiae. The inhibitory mechanisms of the active compounds were analyzed using Lineweaver-Burk plots. The plantextracts were obtained by the maceration method using methanol as the solvent. A significant and linear correlation coefficient between the antioxidant activity and the total phenolic content was found in the methanol extracts. The result revealed that the subtropical plants QuercusgilvaBlume and Quercusphillyraeoides A. Grey had the highest antioxidant activities (IC50) with 38.53±3.10 and 25.00±1.43 μg/mL, respectively, while Mallotusjaponicus and Quercusphillyraeoides A. Grey had the highest α-glucosidase inhibitory activities (IC50) with 8.46±0.30 and 9.88±0.36 μg/mL, respectively. Thus, these plants could potentially be rich sources of natural antioxidants and anti-diabetes medicine.
Indrianingsih et al. (2015) studied this question.