Determination of tea fermentation degree by a rapid micellar electrokinetic chromatography

A micellar electrokinetic capillary electrophoresis (MEKC) method was used to rapidly determine seven tea catechins, three xanthines, gallic acid, vitamin C, theanine and theaflavin in tea. All the compounds were successfully separated (20 kV) within 8 min of migration in the running buffer (pH 7.0) containing 10 mM phosphate, 4 mM sodium tetraborate, 45 mM SDS and 0.5% ethanol. The linear dynamic ranges for polyphenols were from 2.5 (S/N >8) to 100 μg/ml. As revealed by the electropherograms, tea catechins were found to be depleted along with the indoor withering process for making pouching tea, and the fermentation degree can be quantified. The results were compared with the redox potentials of tea infusions.