Structural elucidation and cellular antioxidant activity evaluation of major antioxidant phenolics in lychee pulp

Lychee pulp contains phenolic compounds that are strong antioxidants, but the identities of the major antioxidants present are unknown. In the present study, the major contributors to the antioxidant activity of fresh lychee pulp were identified and their cellular antioxidant activities were investigated. Aqueous acetone extracts of lychee pulp were fractionated on polyamide resin, and those fractions with the largest antioxidant and radical scavenging activities were selected using cellular antioxidant activity and oxygen radical absorbance capacity assays. Three compounds that were major contributors to the antioxidant activity in these fractions were obtained by reverse-phase preparative HPLC and identified as quercetin 3-O-rutinoside-7-O-α-l-rhamnosidase (quercetin 3-rut-7-rha), quercetin 3-O-rutinoside (rutin) and (−)-epicatechin using NMR spectroscopy, HMBC, and ESI-MS spectrometry. The concentration of quercetin 3-rut-7-rha was 17.25 mg per 100 g of lychee pulp fresh weight. This is the first report of the identification and cellular antioxidant activity of quercetin 3-rut-7-rha from lychee pulp.