Isolation and characterization of ellagitannins as the major polyphenolic components of Longan (Dimocarpus longan Lour) seeds

• Published in: Phytochemistry (Oxford) Vol. 77; pp. 226 - 237
• Main Authors: Sudjaroen, Yuttana, Hull, William E., Erben, Gerhard, Würtele, Gerd, Changbumrung, Supranee, Ulrich, Cornelia M., Owen, Robert W.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.05.2012
• Subjects: Antioxidants - chemistry; Antioxidants - isolation & purification; Antioxidants - metabolism; Chebulagic acid; Chromatography, High Pressure Liquid; Corilagin; Dimokarpus; Ellagic acid; Ellagic acid 4-O-α-l-arabinofuranoside; Fluorescence Recovery After Photobleaching; Geraniin; HPLC–ESI-MS; Hydrolyzable Tannins - chemistry; Hydrolyzable Tannins - isolation & purification; Hydrolyzable Tannins - metabolism; Hypoxanthine - chemistry; Isomallotinic acid; Lipid Metabolism; Longan; Mass Spectrometry; NMR; Nuclear Magnetic Resonance, Biomolecular; Phenols - chemistry; Phenols - isolation & purification; Reactive Oxygen Species - chemistry; Salicylic Acid - chemistry; Sapindaceae; Sapindaceae - chemistry; Sapindaceae - metabolism; Seeds - chemistry; Seeds - metabolism; Thailand; Xanthine Oxidase - chemistry; Thailand; Ellagic acid 4-O-α-l-arabinofuranoside; AAPH; Isomallotinic acid; Longan; Corilagin; COSY; SD; cROESY; Dimokarpus; Chebulagic acid; Ellagic acid; Geraniin; BSTFA; IC50; mass spectrometry; ESI; FRAP; DHBA; GC; HPLC; ORAC; COLOC; DPPH; NOE; TPTZ; MS; HMBC; HHDP; DHHDP; NMR; Sapindaceae; HPLC–ESI-MS; TMS; HSQC; XHCORRD
• DOI: 10.1016/j.phytochem.2011.12.008
• ISSN: 0031-9422

The major polyphenolic antioxidant components of Longan seeds are identified as corilagin, chebulagic acid, isomallotinic acid and geraniin. [Display omitted] ► This is a comprehensive report of phenolic compounds present in Longan seeds. ► Phenolic compounds were identified by HPLC–ESI-MS, nano-ESI-MS–MS and NMR (600MHz). ► Complete and unequivocal NMR data is presented for the purified major components. ► The extracts and purified phenolic compounds displayed strong antioxidant activity. Longan (Dimocarpus longan Lour, syn. Euphoria longan Lam.) represents an important fruit in Northern Thailand and has significant economic impact. The fruit is either consumed fresh or as commercially prepared dried and canned products. The canning industry in Thailand produces considerable quantities of waste products, in particular Longan seeds. Because these seeds may be an exploitable source of natural phenolic antioxidants, it was of interest to identify, purify and quantitate the major potential antioxidant phenolics contained therein. The polyphenolic fraction from ground Longan seeds was obtained by extraction with methanol after delipidation with hexane. The hexane extract contained predominantly long-chain fatty acids with major contributions from palmitic (35%) and oleic (28%) acids. The polyphenolic fraction (80.90g/kg dry weight) was dominated by ellagic acid (25.84g/kg) and the known ellagitannins corilagin (13.31g/kg), chebulagic acid (13.06g/kg), ellagic acid 4-O-α-l-arabinofuranoside (9.93g/kg), isomallotinic acid (8.56g/kg) and geraniin (5.79g/kg). Structure elucidation was performed with mass spectrometry and complete assignment of 1H and 13C NMR signals. The methanol extracts exhibited strong antioxidant capacities with an IC50 of 154μg/ml for reactive oxygen species attack on salicylic acid and 78μg/ml for inhibition of xanthine oxidase in the hypoxanthine/xanthine oxidase assay. The extracts were less effective in the 2-deoxyguanosine assay (IC50=2.46mg/ml), indicating that gallates along with ellagic acid and its congeners exert their potential antioxidant effects predominantly by precipitation of proteins such as xanthine oxidase. This was confirmed for the pure compounds gallic acid, methyl gallate, ellagic acid and corilagin.