Changes Of Poly Cyclic Aromatic Hydrocarbons In Dark Tea Processing, Storage, Brewing

Polycyclic Aromatic Hydrocarbons(PAHs) is an organic pollutant extensively existing in environment can cause cancer or induce organism to mutate.Not only can tea leaves’surface and root absorb PAHs, processing can also produce PAHs or adsorb PAHs that is existing around the environment, which can affect the quality of the tea. The selected dark tea leave are relatively coarse and have long processing time and need to brew many times for getting full infusion. Some scholars had detected the levels and sources of polycyclic aromatic hydrocarbons in tea, however still little information about how the change of characteristics of PAHs about tea leaves, processing, storage and brewing. So I establish a high performance liquid chromatography method that can rapidly detect sixteen PAHs in dark tea. By using this method, detecting the concentrations and levels of sixteen PAHs in different fresh tea leaves of three varieties of tea plants followed by three seasons, and dark tea processing, temperature in storage, and brewing. The main research results are shown as follows:(1) Establishing a high performance liquid chromatography method that can rapidly detect sixteen polycyclic aromatic hydrocarbons in dark tea. The results showed that the method was satisfactory when the C18column was used for HPLC, methyl alcohol and ultrapure water was used for mobile phase, the flow rate was set at0.6mL·min-1, the column temperature was set at30℃, the UV detection wavelength was set at274nm, sixteen polycyclic aromatic hydrocarbon can be well separated, the correlation coefficient of16PAHs was more than0.996, detection limit was0.1～1.0μ·gL-1, the detection linearity range was1.0～200.00μg·L-1, the recovery of sample with standard was81.9%～116.5%, the relative standard deviation was less than2%.This method can be used for the detection of sixteen polycyclic aromatic hydrocarbon in dark tea.(2) The concentration of16PAHs of the same part in fresh tea leave were different, variously expressed as summer> spring> autumn in one year, besides this, the concentration of16PAHs in the bud is the lowest, was86.01μg·kg-1. Specifically, Xiangfeicui has highest concentration of16PAHs between Zhenghedabai、Taoyuandaye and Xiangfeicui, which was201.49μg·kg-1,16PAHs are mainly composed of2,3rings, account for about80%. (3) The highest level of16PAHS is summer dark tea, the concentration was419.92μg·kg-1.During the processing, the concentration of16PAHs increased gradually as different process technologies are prepared.(4) During the storage of dark tea, the concentrations of16PAHs decreased gradually as time goes by. Beyond that, to compare common temperature and-20℃, the concentrations of16PAHs under4℃will be the lowest.(5) As dark tea just brewed within1～10min, the concentration of16PAHs increased gradually and reached maximum saturation infusion rate of35.98%,within10～60min, the concentration decreased gradually. At60℃、70℃、80℃、90℃and100℃, infusing tea with boiling water will get the lowest concentration of PAHs.Brewing repeatedly, the average concentration of PAHs in the first-three times was highest, average of concentration was1.21μg·kg-1, till brewing fourth to tenth times, the concentration of PAHS decreased rapidly.(6) According to the national health standards, the content of PAHs in dark tea were set to be0.02～1.77mg·kg-1. In this experiment, the concentration of PAHs in the dark tea we used for detecting was less than the standard.