Commercial samples of green tea, oolong teas and black teas were used. 3 green teas (Westlake Longjing tea, Sanbeixiang green tea, Lushan Yunwu tea), 2 oolong teas (Dense aroma Tieguanyin, Faint scent Tieguanyin) and 1 Yunnan black tea from China were collected by Tea Research Institute, Chinese Academy of Agricultural Sciences.