Separation of epigallocatechin-3-gallate from crude tea polyphenols by using Cellulose diacetate graft BoldItalic-cyclodextrin copolymer asymmetric membrane

Abstract

This study demonstrates a new Cellulose diacetate graft β-cyclodextrin (CDA-β-CD) copolymer asymmetric membrane prepared by a phase inversion technique for the separation of (-)-epigallocatechin-3-gallate (EGCG) from other polyphenols in crude tea. The graft copolymer, CDA-β-CD, was synthesized by prepolymerization of cellulose diacetate (CDA) and 1,6-hexamethylene-diisocyanate (HDI), which was then grafted with β-cyclodextrin (β-CD). Surface and cross-section morphologies of the CDA-β-CD membranes were analyzed by using scanning electron microscopy (SEM). Fourier transform infrared spectroscopy (FT-IR) indicated that the β-CD was grafted onto the CDA by chemical bonding. The influences of the HDI/CDA mass ratio and the catalyst mass fraction on the β-CD graft yield were investigated. The optimum conditions of a HDI/CDA mass ratio of 0.35 g·g^-1 and a catalyst mass fraction of 0.18 wt-% produced a β-CD graft yield of 26.51 wt-%. The effects of the β-CD graft yield and the concentration of the polymer cast solution on the separation of EGCG were also investigated. Under optimum conditions of a β-CD graft yield of 24.21 wt-% and a polymer concentration of 13 wt-%, the purity of EGCG increased from 26.51 to 86.91 wt-%.

Key words： (-)-epigallocatechin-3-gallate (EGCG); tea polyphenols; CDA-β-CD

Acknowledgments

The authors wish to gratefully express their appreciation for the financial support obtained from the National Natural Science Foundation of China (Grant No. 20636010, 20876011 and 20606006), the National Basic Research Program of China (Grant No. 2007CB714304), the National High Technology Research and Development Program of China (Grant Nos. 2007AA100404, 2007AA10Z360), and the Beijing key laboratory of bioprocesses.

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