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Effect of Processing on the Pb and Cu Pollution of Tea

HAN Wen-yan1, 2, LIANG Yue-rong1, YANG Ya-jun2, SHI Yuan-zhi2, MA Li-feng2, RUAN Jian-yun2 (1. Tea Research Institute of Zhejiang University, Hangzhou 310029, China; 2. Tea Research Institute, Chinese Academy of Agricultural Sciences, Key Laboratory of Tea Chemical Engineering,Ministry of Agriculture, Hangzhou 310008, China)  
The effect of processing on the Pb and Cu pollution of tea was studied in this paper. Results showed that tea processing was one of the main pollution sources of Pb and Cu. The extent of pollution was varied with the working procedure, machine and its metal composing. Almost every working procedure, including fresh leaves spreading out or withering, deenzyming, rolling or cutting, fermentation and drying could increase the Pb and Cu concentrations of tea. However, rolling and spreading out were the most important procedures resulting in Cu and Pb pollution, respectively. With the increase of rolling pressure and time, the Cu and Pb concentrations steadily increased. Due to different procedures, especially the rolling pressure and time, the Cu and Pb concentrations of made teas were different, oven dried and roast green tea were the highest, followed by CTC (Crushing, Tearing, Curling) and Orthodox black tea, almost no change in Longjing tea processing. The pollution sources were quite different between Cu and Pb. Cu pollution was mainly from rolling machine and the Cu content of the machine. Cu pollution from rolling procedure accounted for 90% of total one. Pb pollution was mainly due to dust, which came from unclean ground and air in the workshop. Therefore, keeping clean in workshop and regulating the metal constitution of rolling machine could reduce the Pb and Cu pollution during tea processing. In addition, clearing the mature leaves and tea dust away after tea primary processing also could decrease the Pb concentration of tea.
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