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Determination of Tannin in Green Tea Infusion by Flow-Injection Analysis Based on Quenching the Fluorescence of 3-Aminophthalate

Richie L. C. Chen,^† Chun-Hsun Lin,^† Chien-Yu Chung,^† and Tzong-Jih Cheng*^†^‡

Department of Bio-Industrial Mechatronics Engineering, College of Bio-resources and Agriculture, and Department of Biomedical Engineering, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei, Taiwan

J. Agric. Food Chem., 2005, 53 (22), pp 8443–8446

DOI: 10.1021/jf051077f

Publication Date (Web): September 30, 2005

†

College of Bio-resources and Agriculture.

Author to whom correspondence should be addressed [telephone +886-2-33665345; fax +886-2-23627620; e-mail tzongjih@ntu.edu.tw].

‡

National Taiwan University Hospital, College of Medicine.

Abstract

A flow-injection analytical system was developed to determine tannin content in green tea infusions. The flow-injection system is based on measuring the quenching effect of tannin on the fluorescence of 3-aminophthalate. Fluorophore was obtained by auto-oxidation of luminol during solution preparation. System performance was satisfactory for routine analysis (sample throughput >20 h^-¹; linear dynamic range for tannic acid, 0.005−0.3 mg/mL; linear dynamic range for green tea tannin, 0.02−1.0 mg/mL; CV < 3%). The flow-injection method is immune from interference by coexisting ascorbate in green tea infusion. Analytical results were verified by the ferrous tartrate method, the Japanese official analytical method.

Keywords: Flow-injection; tannin; fluorescence; quenching; luminol; 3-aminophthalate; green tea

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