Abstract
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.
Highlights
Fluorine (F) is an important element to human health and a moderate F intake is confirmed to be beneficial to alleviation of dental caries (Levi et al, 1983; Ermis et al, 2003)
The duration of fast stage 1 depended on leaf particle size and temperature
When the tea was infused in 50°C water for 20 s and the residue leaf was re-infused in boiling water for 5 min, 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
Summary
Fluorine (F) is an important element to human health and a moderate F intake is confirmed to be beneficial to alleviation of dental caries (Levi et al, 1983; Ermis et al, 2003). Tea is a fluorine accumulator (Lu et al, 2004) and F content in mature tea leaves was 1000 times higher than water-soluble F level in the soil on which it is grown (Fung et al, 1999). Different types of tea usually have different concentrations of F owing to the difference in maturity of tea material, processing method and brewing style (Gulati et al, 1993; Sha and Zheng, 1994; Fung et al, 1999; Ruan and Wong, 2001; Shu et al, 2003; Lu et al, 2004). Particle size of tea leaf is an important factor influencing diffusion kinetics of solutes (Ye et al, 2007) and few studies on this topic in relation to F extraction of tea are available. The present study aims at investigating the F release characteristics from tea samples with various particle sizes under different extraction conditions including temperature and extraction time
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