Abstract: In this study, absorption, transportation and bioavailability of fluorine in different extracts of a dark tea were evaluated in the Caco-2 cell line model. The results show that the fluorine contents in different extracts of dark tea were significantly different. The fluorine content of the crude polysaccharide fraction (RTP) was the highest, which was 2.17 times that of the water extract (TE). Fluorine content in dialyzed polysaccharide (DTP) was significantly reduced, which was only 1/22 of the fluorine content in RTP and 1/10 of the fluorine content in TE. The forward and reverse transport of fluorine in cell model had time and dose effects, and increased with the increase of time and concentration. After the first 1 h treatment, the forward and reverse transport of fluorine in NaF was the highest, while that in DTP was the lowest, which were significantly different from other treatments. There was no significant difference between the TE and RTP treatments. The apparent permeability coefficient (P_app) decreased with the prolonging of treatment time. The P_app of fluorine in NaF was more than 1×10^-5 cm·s^-1 within 4 h, indicating its bioavailability was good. The P_app of fluorine in TE and RTP decreased to less than 1×10^-5 cm·s^-1 after 2 h of treatment, indicating its bioavailability was moderate. the P_app of fluorine in DTP was the smallest at all stages, and was less than 1×10^-5 cm·s^-1 after 1 h of treatment, indicating its bioavailability was low. Fluorine in NaF, TE or DTP was mainly transported by passive diffusion within the tested concentration range, while fluorine in RTP had an active transport at a higher concentration. In conclusion, in the intestinal epitheliums model, the fluorine in the dark tea has lower bioavailability than that in NaF, and the binding form of the fluorine in the dark tea might affect its bioavailability.

Key words: dark tea, fluoride, Caco-2, transport, bioavailability