Structure analysis of an acidic polysaccharide isolated from green tea

Abstract

An acidic polysaccharide (ATPS-2) was isolated and purified from coarse green tea. ATPS-2 with peak molecular weight of 4430 Da was composed of rhamnose, arabinose, galactose and galacturonic acid. Structure features of the purified ATPS-2 were investigated by a combination of chemical and instrumental analysis, such as periodate oxidation, Smith degradation, ¹H NMR, ¹³C NMR, COSY, HSQC, HMBC and ROESY spectrum. It was found that ATPS-2 was a pectic polysaccharide. The backbone proved to consist of the smooth region of α-1,4-D-galactopyranosyluronan blocks interconnected by 1,2-linked rhamnose residues involved in the linear sugar chain. The ramified hairy regions were shown to contain the following of the backbone: →4)-α-D-GalpA-(1 → 2)-α-L-Rhap-(1 → 4)α-D-GalpA-(1→ and the side chains attached to the residues of rhamnopyranose of these fragments. The backbone galacturonic acid residues of ATPS-2 were partially O-methyl esterified and acetylated. The side chains contain linear and branched α-L-Araf and β-D-Galp residues.

Keywords:

• green tea
• acidic polysaccharide
• structure
• NMR

Acknowledgements

We are grateful to Dr Dong Qun (Shanghai Institute of Materia Medica, Chinese Academy of Sciences) for his skillful technical assistance in conducting the NMR analysis. This work was sponsored by China's Strategic Hi-Tech Research and Development Plan (Chinese National 863 Plan, Grant No. 2008AA10Z322), Shanghai Rising-Star Program (Grant No. 07QB14047), and Shanghai-Unilever Research and Development Foundation (Grant No. 05SU7094).