title: Preparation of free, soluble conjugate, and insoluble-bound phenolic compounds from peels of rambutan (Nephelium lappaceum) and evaluation of antioxidant activities in vitro.
abstract: The soluble phenolic compounds of rambutan peels (RP) were extracted by microwave-assisted extraction (MAE) and the operating parameters were optimized. The optimal conditions obtained were ethanol concentration of 80.85%, extraction time of 58.39 s, and the ratio of liquid to solid of 24.51:1. The soluble phenolic content by MAE was 213.76 mg GAE/g DW. The free, soluble conjugate, and insoluble-boaund phenolic compounds were prepared by alkaline hydrolysis, and the contents of 3 fractions were 185.12, 27.98 and 9.37 mg GAE/g DW, respectively. The contents of syringic acid and p-coumaric acid were high in the free fraction, showing 16.86 and 19.44 mg/g DW, and the soluble conjugate and insoluble-bound phenolics were mainly composed of gallic acid and caffeic acid. Furthermore, the antioxidant activities of 3 fractions were evaluated in 5 model systems. Results indicated that the free fraction had high antioxidant activities, compared with the soluble conjugate and insoluble-bound fractions.
authors.affiliation: Research Center of Food Engineering, College of Chemistry and Engineering, Kunming Univ of Science and Technology, Kunming, Yunnan 650224, China.
authors.forename: Liping
authors.initials: L
authors.lastname: Sun
authors.forename: Huilin
authors.initials: H
authors.lastname: Zhang
authors.forename: Yongliang
authors.initials: Y
authors.lastname: Zhuang
mesh_terms: D000975:Antioxidants / Q000494:pharmacology*; D002109:Caffeic Acids / Q000032:analysis; D003373:Coumaric Acids / Q000032:analysis; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000032:analysis; D015227:Lipid Peroxidation; D010636:Phenols / Q000494:pharmacology*; D010936:Plant Extracts / Q000494:pharmacology*; D011422:Propionates; D029631:Sapindaceae / Q000737:chemistry*
chemical_list: D000975:Antioxidants; D002109:Caffeic Acids; D003373:Coumaric Acids; D010636:Phenols; D010936:Plant Extracts; D011422:Propionates; D005707:Gallic Acid; C001945:syringic acid; C495469:p-coumaric acid; C040048:caffeic acid