The total aerobic bacteria counts were determined by pouring 0.1 ml of diluted sample onto Plate Count Agar (Aoboxing Bioscience Inc, Beijing, China). The plates were incubated at 35 °C for 48 h, and the colonies were counted. Mould and yeast counts were determined by pouring 0.1 ml of the diluted sample onto potato dextrose agar plates (Aoboxing Bioscience Inc, Beijing, China), then incubated at 25 °C for 5 days, and the colonies were counted. Coli-forming bacteria counts were determined by pouring 0.1 mL of the diluted sample onto chromocult coliform agar (Merck Co, Germany), then incubated at 35 °C for 48 h and the colonies were counted.