Antibacterial Substances in Green Tea Extract

Abstract

Antibacterial substances in hot-water extract (110°C, 15min) of a green tea product was investigated. The experimental results obtained were as follows.
1. Antibacterial effects of the green tea extract appeared to be conspicuous on Vibrio metschnikovii and Alcaligenes faecalis. These bacteria were found to be about ten-times as sensitive as Staphylococcus aureus to the extract.
2. The green tea extract was adsorbed to casein and the tannin fraction, which showed antibacterial effects, was eluted from the adsorbent with 90% aq. acetone. Five catechins were separated from the tannin fraction by paper chromatography and their contents were quantitatively determined. The minimum inhibitory concentrations (mcg/ml) of these catechins on V. metschnikovii were: epigallocatechin 20, epigallocatechin gallate 45, epicatechin gallate 45, gallocatechin 50, and epicatechin 75.
3. Addition of caffeine at a concentration of approx. 1mg/ml showed a marked synergetic effect to increase the antibacterial titre of catechins (ca. 4mg/ml). However, caffeine itself (2mg/ml) had no antibacterial action.
4. An aqueous solution containing the above five catechins and caffeine at the same concentrations as in the green tea extract showed a similar antibacterial titre to that of the extract.