Abstract: This study was designed to analyze phenolic compounds in different solvent (aqueous, ethyl acetate and 1-butanol) fractions of the ethanol extract of longan seeds by high-performance liquid chromatography coupled with electrospray ionization mass spectrometry (HPLC-ESI-MS) and to evaluate their antioxidant activity. A total of 11 compounds were identified in aqueous, ethyl acetate and 1-butanol fractions, including 6 phenolic compounds. Ethyl acetate fraction had the strongest antioxidant activity among the three fractions. Further separation of ethyl acetate fraction by macroporous resin AB-8 column chromatography resulted in 16 eluates. The measurement of DPPH free radical scavenging activity and reducing potential using ascorbic acid as a reference substance demonstrated that all the eluates had excellent antioxidant activity and eluates No. 7 and 8 had the strongest antioxidant activity. Highly pure gallic acid was obtained after repeatedly recrystallizing eluate No. 7, thus supporting the excellent antioxidant activity of the eluate. Meanwhile, the strongest antioxidant activity of ethyl acetate fraction as a low-polarity fraction indicated that longan seeds contained abundant amounts of phenolic compounds having small molecular weight.

Key words: longan seed, high-performance liquid chromatography coupled with electrospray ionization mass spectrometry (HPLC-ESI-MS), antioxidant activity, DPPH radical, reducing power