Polycyclic Aromatic Hydrocarbons In Tea: Concentration, Source And Risk

The sanitary quality of tea leaves might pose a health threat on tea drinkers. Polycyclic aromatic hydrocarbons (PAHs), a well-known class of carcinogens in food nowadays, might impact the quality of tea leaves. PAHs contents in certain kinds of made teas had been determined. However, little information is available on the source of PAHs in tea leaves, and their impact on the quality of tea leaves, and their health risk. These are the bases to prevent tea leaves from PAHs pollution.In this dissertation, the PAHs contents in some main kinds of made teas were determined; the source of PAHs in tea leaves was studied based on the research of the fresh leaves accumulation and the impact of manufacturing process; the impact of PAHs on the tea quality were preliminary studied; the sanitary standards for the PAHs were promoted based on the evaluation of their health risk. The main conclusions are shown as follows.(1) The total contents of the 16 PAHs (∑PAHs) in the tea samples ranged from 323 μg/kg to 8800 μg/kg with the highest ∑PAHs found in the black tea. 3-4 rings PAHs were dominant in all tea samples, with a contribution of 77.7%-98.7% to the ∑PAHs.(2) The fact that the PAHs contents in the tea tree above the ground in the tea garden were larger than that below the ground, indicating that PAHs in the fresh tea leaves were mainly originated from the air. The root and fresh leaves of tea tree can absorb large quantity of PAHs from the around environment. The root concentration factors (RCFs) for PAHs were increased directly with the increase of lgK_ow. The leaves concentration factors (FCFs) for PAHs were increased exponentially with the increase of lgK_owl. The transport factors (TFs) of PAHs from tea root to tea leaves were decreased exponentially with the increase of lgAK_ow. The TF of NA reached 22.8%, while the TF of PHEN and PY were only 0.016% and 0.004%, respectively.(3) The combustion of pine firewood during the drying stage released large quantity of PAHs, which were then absorbed by tea leaves, and thus resulting in the high PAHscontents in the black tea.(4) PAHs can impact the contents of catechins and caffine in fresh tea leaves.(5) The release rates (RR) of PAHs from the made tea to the liquor were inverse proportional to the lgK_ow of the PAHs. Sanitary standards of the 16 PAHs for tea leaves were calculated to be 0.10-110 mg/kg.