Tea extraction methods in relation to control of epimerization of tea catecnins

Effect of water temperature and ethanol concentration on epimerization and extractability of tea catechins was investigated. The results showed that epigallocatechin gallate (EGCG) and epicatechin gallate (ECG) were partially epimerized into gallocatechin gallate (GCG) and catechin gallate (CG), respectively, when tea catechins extract was heated in water solution at 100 degrees C for 2 h or dry tea was extracted in water at 100 degrees C. The epimerization of the catechins was inhibited if the tea catechins extract was heated as solid powder and the dry tea was extracted in 50% (v/v) ethanol or in water at 80 degrees C or below. When the dry tea was extracted in water, the extractability of catechins increased with the increase of extraction temperature up to 100 degrees C, but there was no statistically significant difference in total catechins between 80 degrees C and 100 degrees C. When teas were extracted using ethanol solutions, the highest extractability of total catechins was obtained in 50% (v/v) ethanol for dry tea and in 75% (v/v) ethanol for fresh tea leaf. In order to reveal the real profiles of tea catechins in teas to be tested, dry tea should be extracted in 50% (v/v) ethanol for 10 min, while fresh tea leaf should be extracted in 75% (v/v) ethanol for 10 min. For commercial extraction, temperature should be controlled at 80 degrees C if water is used as the solvent. (c) 2007 Society of Chemical Industry.