2.2. DNA extraction
Total DNA in the food samples was extracted and purified using the DNeasy_ blood and tissue kit according to the manufacturer’s instruction. Briefly, 50 mg of crushed sample were digested in the lysing buffer, and the lysate was transferred into a mini silica gel column. After centrifuging at 10,000 g for 1 min, the column was washed twice by the washing buffer, and the purified DNA was eluted by TE buffer. The DNAs from raw pork, beef, chicken and mutton (including meat from goat and sheep) were extracted as the positive controls and those from donkey, horse, fish and soybean as negative controls. The concentration and purity of the DNA were examined spectrophotometrically at 260 nm and 280 nm.