Antioxidant and Anti-diabetic Properties of Aqueous Methanol Extraction of Nephelium mutabile (Pulasan) Leaves

Nephelium mutabile is a tropical plant of Sapindaceae family which originated from the Malay Peninsula and used in traditional medicine. This study focused on investigating the antioxidant and anti-diabetic properties of Nephelium mutabile leaves. The aqueous methanol (80%) crude extract of Nephelium mutabile leaves were fractionated via gravity column chromatography and thin-layer chromatography. A total of 17 fractions were obtained from column chromatography and subsequently pooled together to yield eight fractions. The pooled fractions were examined for their antioxidant properties via DPPH assay, Folin-Ciocalteu assay, and aluminum chloride colorimetric assay and tested for anti-diabetic properties using alpha-amylase and alpha-glucosidase inhibitory assay. DPPH assay showed that fraction 8 has the highest free radical scavenging activity (EC50 =88.0 μg/mL) followed by fraction 7 (EC50 =225.0 μg/mL). Fraction 8 showed the highest total phenolic and flavonoid content (221.1 μg GAE/mg, 222.4 μg QE/mg) respectively followed by fraction 7 (166.5 μg GAE/mg, 213.9 μg QE/mg) respectively. The most potent alpha-amylase inhibitory activity is observed in fraction 8 with an IC50 value of (41.0 μg/mL) followed by fraction 7 (90.6 μg/mL). In the alpha-glucosidase inhibitory activity, fraction 8 with IC50 value 160.0 μg/mL followed by fraction 7 with IC50 value 50.6 μg/mL showed the best inhibition activity. In conclusion, Nephelium mutabile leaves showed potential antioxidant, and anti-diabetic properties and fractions 8 and 7 should be the focus of future studies.