Analysis of Combined Caffeine Proportion in Different Tea

The content of caffeine and proportion of combined caffeine in different tea was investigated in order to provide some theories for accurate analysis of caffeine in tea, monitoring the oxidation degree of tea polyphenols during tea processing and study on different function of caffeine in different tea. The representative teas of China's six major teas were selected as test samples. The caffeine content and proportion of combined caffeine in tea was determined by the method of low-pH precipitation and HPLC. The results showed as follows: fermented Pu-erh tea and Liubao dark tea were complete fermentation tea and the proportion of combined caffeine in these teas was the biggest (about 20%). However, the proportion of combined caffeine in the non-fermentation tea, that is green tea, was the smallest (2%). So, we can conclude that the proportion of combined caffeine is directly proportional to the oxidation degree of tea polyphenols. The combined caffeine proportion can be applied to judge the oxidation degree of tea polyphenols of tea during processing and investigate the different function of caffeine in different tea.