Abstract
The purpose of this study was to investigate the concentration of fluoride in various kinds of tea and the conditions of infusing. The samples of tea-leaves used were each of the regular and highgrade green teas made in Uji and Shizuoka prefecture, regular and high-grade roasted tea made in Shizuoka prefecture, oolong tea made in China and black tea made in Sri Lanka. We used green tea produced in 1996 as an old tea and that produced in 1997 as a new one. The temperature of the tea infusion was at 50°C,60°C,70°C,80°C and 90°C, and tea was infused for 30 sec,1 min,2 min,5min and 10 min. The highest concentration of fluoride was found in black tea, followed by roasted tea, green tea and oolong tea at any temperature for any length of time infused. Whereas, roasted tea had the highest concentration of fluoride, followed by oolong tea, green tea and black tea when teas were exuded overnight with water at room temperature. The fluoride concentration of the low-grade green tea was higher than that of high-grade green tea. We suggest that low-grade green tea-leaves contain a high concentration of fluoride. In conclusion, we suggest that the fluoride concentration of tea infusion depends on the fluoride concentration of the local soil and on the production method. We confirmed that the fluoride concentration of the regular green tea is higher than that of the high-grade one.
