Influence of Microwave on Extraction, Structure and Catechin Composition of Tea-Polyphenol

Using mid grade and low grade green tea as raw material, the influence of microwave on the extraction, structure and catechin composition of tea polyphenol was studied. Using purified water as the solvent, microwave treatment could improve leaching tea polyphenols.The green tea of size 0.246 mm was leached 2 times by microwave (material water ratio 1∶20,Time:3 min).Then the tea was leached 1 times in 10 minutes by purified water (50 ℃) . The result showed that the leaching rate of tea polyphenols was 90.73%, which was higher than that of being leaching by the mixture of ethyl alcohol and water. The analysis of HPLC demonstrated that the tea polyphenols production prepared by microwave treatment mainly contained three kinds of catechin: EGC, EGCG and ECG. The total production of catechin constituted 78.4% of tea polyphenols, among which the content of EGCG was the highest and constituted about 45.8% of the total production of catechin in comparison with the tea polyphnols extracted by the mixture of ethyl alcohol and water. Among the tea polyphenols production extracted by microwave treatment, there was a little alteration in catechin composition and it had a slight decrease to the contents of EGCG and ECG. But the decreasing amount was far lower than that by boiling water extraction. The analysis of ultra violet visible light spectra and infra red spectra confirmed that microwave had no influence on the chemical structure of tea polyphenols.