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Preparation of Free, Soluble Conjugate, and Insoluble-Bound Phenolic Compounds from Peels of Rambutan (Nephelium lappaceum) and Evaluation of Antioxidant Activities in vitro

Authors

  • Liping Sun,

    1. Authors are with Research Center of Food Engineering, College of Chemistry and Engineering, Kunming Univ. of Science and Technology, Kunming, Yunnan 650224, China. Direct inquiries to author Zhuang (E-mail: kmylzhuang@yahoo.com.cn).
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  • Huilin Zhang,

    1. Authors are with Research Center of Food Engineering, College of Chemistry and Engineering, Kunming Univ. of Science and Technology, Kunming, Yunnan 650224, China. Direct inquiries to author Zhuang (E-mail: kmylzhuang@yahoo.com.cn).
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  • Yongliang Zhuang

    1. Authors are with Research Center of Food Engineering, College of Chemistry and Engineering, Kunming Univ. of Science and Technology, Kunming, Yunnan 650224, China. Direct inquiries to author Zhuang (E-mail: kmylzhuang@yahoo.com.cn).
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Abstract

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.

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