1. Department of Public Health Laboratory Sciences, West China College of Public Health, Sichuan University, Chengdu, Sichuan 610041, P. R. China
2. Department of Nutrition and Food Safety, West China College of Public Health, Sichuan University, Chengdu, Sichuan 610041, P. R. China
3. Shijiazhuang Junlebao Dairy Co., Ltd., Shijiazhuang, Hebei 050221, P. R. China