Milk samples: Twelve lots of bovine milk from each different step of the processing of milk (raw, pasteurized and sterilized) were collected at a dairy factory in the region of Vale do Taquari, in the Brazilian state of Rio Grande do Sul. The same lot of raw milk was submitted to pasteurization (75°C for 15 sec) and then to ultra-high temperature process (140°C for 3 sec). The pasteurization was realized on tetra pack equipment with 30,000 L h–1 and after this process the milk was maintained at 4°C. Each lot was sampled three times in order to perform analysis in triplicates. Raw, pasteurized and UHT milk samples were transferred to sterilized tubes. The tubes were immediately cooled at 4°C after sampling and transported in thermal containers.