Structural elucidation of phenolic antioxidants from Litchi (Litchi chinensis Sonn.) skin and seeds

Abstract

Plant phenolics possesses many potent biological activities. Recently, the investigation of phenolics in inexpensive sources are interesting. The skin and seeds of Litchi (Litchi chinensis Sonn.) were extracted with Soxhlet apparatus. The methanolic extract was analyzed by using analytical high performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS). The seeds contained procyanidin oligomers, p-coumarate quinate esters, epicatechin and rutin. The major phenolic components in skin were similar to seeds, however, p-coumarate quinate esters were not detected. Individual phenolic compounds were purified by semi-preparative HPLC and fraction collector in order to elucidate the structures with electrospray ionization mass spectrometry (ESI-MS), and nuclear magnetic resonance spectroscopy (NMR). The antioxidant potential of crude extract was high when testing with hypoxanthine/xanthine oxidase enzyme (HX/XO) and 2-deoxyguanosine assays.