Kinetic study on leaching of fluorine from green tea

Kinetic behaviors of fluorine leaching from tea were studied. The leaching process of fluorine could be divided into initial fast stage and later slow stage. The duration of fast stage 1 depended on leaf particle size and temperature. The higher the temperature and the smaller the leaf particle size, the shorter the duration of initial fast stage. Based on the test results, a two-step infusion method was developed to control fluorine level in tea liquor. When the tea was infused in 50°C water for 20 s (first infusion) and then the residue leaf was re-infused in boiling water for 5 min (second infusion), more than 26% of total fluorine was removed during first infusion, but more than 80% of catechins and caffeine of the teas remained in the second infusions which had a F level 0.70 mg L-1 or less. It reflected that the two-step infusion method is an alternative to control excessive fluorine exposure for tea drinkers.   Key words: Green tea, fluorine, kinetics, diffusion coefficients, two-step infusion.