Antioxidant activity and chemical constituents of some Indonesian fruit peels

The ethanolic extracts and their fractions of some Indonesian fruit peels were screened for their free radical scavenging properties using vitamin-E as standard antioxidant. Free radical scavenging activity was evaluated using 1, 1-diphenyl-2-picrylhydrazyl (DPPH) free radical. The strongest antioxidant activity was shown by the Rambutan (Nephelium lappaceum Linn.), followed by Kelengkeng (Euphoria longan Lour. Steud) and Durian (Durio zibethinus Murr.) with IC₅₀ values of 7.74, 11.85, and 28.83 μg/mL, respectively comparable to vitamin-E (IC₅₀ = 8.48 ± 0.1 μg/mL). The ethyl acetate fraction of these fruit peels extracts demonstrated the most active antioxidant activity compared with hexane, chloroform and methanol fractions. The chemical constituents of Rambutan and Durian were successfully isolated using vacuum liquid chromatography and radial chromatography technique, and these structures were characterizated based on the proton (1H) and carbon (13C) NMR spectra. The isolated compounds were ethyl gallate (1) from Rambutan (Nephelium lappaceum Linn.) rind, 4, 4-dimethylporiferasta-18(19)-en-3-ol (2) and 3α-E-ferulyloxy-lup-20(29)-en-28-oic acid (3) from Durian (Durio zibethinus Murr.) peels. The results showed that prospective antioxidant contents in Rambutan's fruit peel extract was higher than Kelengkeng and Durian fruit peel extracts.