Antioxidant activity and chemical constituents of methanolic extract of Durio zibethinus Murr. (durian) peels

This study aimed to determine the DPPH free radical scavenging activity, total phenolic content (TPC) and total flavonoid content (TFC) of methanolic extract of Durio zibethinus Murr. (durian) peels and its fractions. The chemical constituents of durian peels extracted into methanol by soxhlet extraction were sequentially extracted into hexane, dichloromethane and aqueous methanol. Among the fractions, the dichloromethane fraction showed the highest DPPH free radical scavenging activity (IC₅₀ 179.9 ± 6.6 μg/ml) with high TPC and TFC (85.82 ± 12.11 mg gallic acid equivalent/g of dried weight of extract and 12.66 ± 1.94 mg of quercetin equivalent/g of dried weight of extract, respectively). A very strong positive correlation (r = 0.9677) was observed between the DPPH free radical scavenging activity and the TPC of fractions and a strong positive correlation (r = 0.7858) was noticed between the DPPH free radical scavenging activity and TFC of the fractions indicating that phenolic compounds in durian peels may contribute to their strong antioxidant activity. As the dichloromethane fraction had constituents with the highest antioxidant activity, it was analyzed by Gas chromatography-Mass spectrophotometry to identify its volatile constituents. The results revealed that the dichloromethane fraction was rich in [1,2-Benzenedicarboxylic acid, bis (2-ethylhexyl) ester], [2,3-diphenylquinoxaline], [2-coumaranone], [4-((1E)-3-hydroxy-1-propenyl)-2-methoxyphenol], [7,9-di-tert-butyl-1-oxaspiro (4,5) deca-6,9-diene-2,8-dione] and [phenol, 2,4-bis(1,1-dimethylethyl)], which are known to exhibit antioxidant activity.