Survival of Escherichia coli O157:H7 and Staphylococcus aureus during the fermentation and storage of kefir

The survival of Escherichia coli O157:H7 and Staphylococcus aureus, which are foodborne pathogens was investigated during fermentation and storage of kefir. The kefir grains were inoculated with 5% of the whole fat UHT cow milk and the E. coli O157: H7 and S. aureus cultures were added separately to give 10(5) cfu mL(-1) and left to incubate at 22 degrees C for 24 hours at first stage. During the incubation, the bacteria and yeast counts, pH and titratable acidity amounts were determined. In the second stage, E. coli O157:H7 and S. aureus cultures were separately added to produce 10(5) cfu mL(-1) of kefir and was stocked at 5 degrees C for 3 days. Every day samples were taken and the same tests were done. During fermentation, in all samples the initial while TA was 0.14%, the fermentation was 1.0% and 1.01% at the end. The kefir samples were pH 4.5 at the end of the 3 day period of storage. S. aureus was significantly inhibited while E. coli was not inhibited during the fermentation process. During storage, E. coli O157:H7 and S. aureus were inhibited within 2 days. The kefir has the quality of being a healthy product during fermentation and storage.