Residue Pattern Of Polycyclic Aromatic Hydrocarbons In Tea Leaves,Green Tea Manufacturing Procedures,and Tea Infusion

Residues of certain chemical contaminants in tea leaves pose threat to the health of tea drinkers,since it not only significantly affect on tea consumers,but also causes considerable economic losses of tea exports in China.However,because of long plantation time and complex processing,tea buds or leaves inevitably adsorb and accumulate certain environmental contaminants.Polycyclic aromatic hydrocarbons?PAHs?are ubiquitous environmental pollutants and consist of two or more condensed aromatic carbon rings.PAHs received the foremost attention because of their mutagenic and carcinogenic effects.Tea plant leaves could strongly accumulate PAHs from around the air environment.Orthodox tea,which is dried by combustion gases produced from burning of wood,or coal,is seriously contaminated with PAHs.However,mechanization and automation are widely used in green tea manufacturing,and tea leaves are air-dried generally through electric heating.The residues of PAHs in tea fresh leaves might be the main source of PAHs in the tea product.PAHs contents and distribution characteristics in fresh tea leaves were discussed in this study.The obtained results are useful for ascending the PAHs resource of tea.Orthodox black tea,which is dried by combustion gases produced from burning of wood,oil,or coal,is seriously contaminated with PAHs.However,PAHs contents in green tea in different manufacturing stages have not yet been investigated.Studies on dissipation behaviour of PAHs during green tea manufacturing processes would therefore provide useful information for ascending the PAHs resource of green tea and in formulating the maximum residue level for PAHs in tea.In this study,a method for PAHs in tea matrices was developed and validated.Then residues levels of PAHs in tea fresh leaves from different area.Residue pattern of PAHs in tea leaves during green tea manufacturing and transfer rates of PAHs from made tea into infusion were investigated.There results are as follows:?1?A QuEChERS method for PAHs in tea matrices was modified by comparing the extraction efficiency with the treatment of different volumes of n-hexane during LLE,the adsorption ratio of adsorbents(PSA,florisil,C₁₈,MgSO₄)on PAHs,and the purification effects of these adsorbents on tea matrices.PAHs in tea matrices were determined by gas chromatography–tandem mass spectrometry?GC–MS/MS?.The loss of PAHs that occurred during sample preparation were calibrated by isotopic surrogate standards.The recoveries for PAHs were 77%¹07%,with RSDs less then 13%.The LODs and LOQs of PAHs in tea matrices were 0.1⁰.7?g/kg and 0.4².6?g/kg,respectively.Satisfactory recoveries and deviations were obtained from the spiked tea samples.The developed method is stable and reliable,which fulfils the requirement for a routine analysis of PAHs in tea matrices.?2?Residues of PAHs in tea fresh leaves were determined using GC-MS/MS to study their concentration in tea fresh leaves.Contaminated levels of 15PAHs in tea fresh leaves were found to be relative with the environmental quality in the production areas of tea.Total concentrations of 15PAHs in the tea buds and tender leaves decreased with increasing distance from the road.However,PAHs contamination for tea garden within 50 m from traffic exhausts was more seriously.Total concentrations of 15PAHs in the tea buds,tender leaves,and old leaves were 40.5⁵2.8?g/kg,50.0⁶7.4?g/kg and91.5⁹7.6?g/kg,respectively,and expressed as:tea buds<tender leaves<old leaves.?3?During the manufacture of green tea by using the electric heating model,evaporation of moisture and PAHs during tea processing were the key factors affecting PAHs residue content in product intermediates and green tea.PAHs residues in tea leaves increased from 44.8⁸2.1?g/kg to135.7²24.9?g/kg after the manufacture of green tea by using the electric heating model.The increasing PAHs contents in tea leaves during manufacture resulted mainly from the reduction in moisture percentage.Whereas PAHs residues in tea leaves decreased from 215.0³89.2?g/kg to140.3²32.5?g/kg during green tea processing because of large amount of PAHs evaporation in the step of spreading and drying.?4?The transfer rates of 15PAHs residues from green tea to infusion increased from 4.6%to 7.2%,and PAHs leaching was higher in 1st tea infusion than in 2nd tea infusion.PAHs with low water solubility and high octanol–water partition coefficient?Kow?were extracted considerably more easily in the 1st tea infusion than in the 2nd tea infusion.