Isolation of active compound from Nephelium lappaceum L. rind as an antioxidant

Abstract

The consumption of rambutan (Nephelium lappaceum L.) results in a vast amount of rambutan rind. It is very interesting to explore rambutan rind as natural antioxidants. This study aimed to explore the antioxidant activities of rambutan rind in vitro and to correlate those activities with a group of compounds (phenolics and flavonoids). Rambutan rind was cleaned, dried using a conventional oven, powdered, and the powder obtained was subjected to maceration. The macerate was fractionated using petroleum ether and chloroform to get chloroform fraction. The sub fractionation was done toward chloroform fraction. The chloroform fraction and its subfractions were then subjected to antioxidant activity measurement, determination of phenolics and flavonoid contents, and the active compound present in the most active subfractions was isolated using column chromatography. The isolate was identified using several methods including thin-layer chromatography (TLC), Fourier transform infrared (FTIR) spectroscopy as well as gas chromatography-mass spectrometry (GC-MS). The results showed that the chloroform fraction and its subfractions were correlated with the phenolic and flavonoid contents found in rambutan rinds. The phenolic and flavonoid content of chloroform fraction was 32.32±0.79 and 55.05±3.900, respectively, whereas the IC50 of antioxidant activity was 49.77±0.22 for DPPH and 45.36±0.27 for ABTS. The reducing power was 34.478±0.245 (mg vitamin C equivalent/g sample) and the metal chelating activity was 332.753±0.695 (mg Na EDTA equivalent/g sample). The phenolic contents contributed towards the metal chelating activities compared to other antioxidant activities with an R 2 value of 0.8726, while flavonoid contents contributed more to ABTS radical scavenging activity with an R 2 value of 0.8916. One of the active compounds present in rambutan rind having antioxidant activity was identified as 1,2-benzenedicarboxylic acid. Thus, the under-utilized part of rambutan rind could be explored as a natural antioxidant to be used as a food supplement