Determination of Tea Catechins in Food by HPLC with an Electrochemical Detector

To develop a method for determination of tea catechins in food by HPLC with an electrochemical detector, we examined the responses of an electrochemical detector to tea catechins. Five catechins ((+)-catechin, (-)-epicatechin, (-)-epigallocatechin, (-)-epicatechin gallate, (-)-epigallocatechin gallate) started to show a response at the applied potential of +400mV, and the maximum response was observed at about +800mV. The content of tea catechins in food is relatively high, and the sensitivity of the electrochemical detector to tea catechins was about one thousand times higher than that of the UV detector. Generally, an electrochemical detector responds to many substances as the applied potential is increased. We concluded that for the analysis of tea catechins in foods a suitable applied potential of the electrochemical detector is +500-+600mV. The detection limit for the tea catechins was about 0.2pmol (40pmol/ml) under the conditions used. When an extract from canned green tea was examined, gallic acid, gallocatechin and gallocatechin gallate were selectively detected in addition to the five catechins indicated above. Methylxanthins and vitamin C, which are often found in large amounts in green tea, did not interfere with determination of the tea catechins. These results indicated that the HPLC-electrochemical detector method is highly selective and appropriate for the determination of tea catechins in food.