Survival of Escherichia coli O157:H7 in the processing and postprocessing stages of acidophilus yogurt

In this study the survival of Escherichia coli O157:H7 in the production process of acidophilus yogurt was examined and compared with traditional yogurt. Milk was inoculated with different doses of E. coli O157:H7 (10^2, 10^4 and 10^6 CFU mL^-1) and two kinds of yogurt were produced. Samples were taken for pH measurements and bacterial enumeration at 0, 3, 24, 48, and 72 h after inoculation. Escherichia coli O157:H7 was analysed by using a Most Probable Number technique and yogurt starter culture and Lactobacillus acidophilus were counted by using classical culture methods. Elimination times of E. coli O157:H7 were determined for 10^2 CFU mL^-1 as 3 h, and for 10^4 and 10^6 CFU mL^-1 as 48 h in acidophilus yogurt. Elimination times in traditional yogurt were 48 h for 10^2 and 10^4 CFU mL^-1 and 72 h for 10^6 CFU mL^-1E. coli O157:H7. In conclusion, the elimination time of E. coli O157:H7 in acidophilus yogurt was shorter than in traditional yogurt during the processing and post-processing stages.