Artificial contamination
15 pasteurized milk samples and 15 UHT milk samples randomly selected were artificially contaminated. These samples were divided into two groups, one group was contaminated with a culture of the Enterobacteriaceae family (Salmonella Typhimurium ATCC 14028) and another group with a negative control culture, a strain of Staphylococcus aureus (ATCC 02923). The cultures were reactivated in nutrient broth (Oxoid, Ltd, Basingstoke, UK) and incubated at 37 °C for 18 h (Owen et al., 2010).