Effects of tarhana fermentation and drying methods on the fate of Escherichia coli O157: H7 and Staphylococcus aureus

As a traditional fermented product tarhana is the dry form of yoghurt-cereal mixture and form an important part of diets of many people in Turkey. Organic acid production during the fermentation and lowering the moisture content below 10% by drying have bacteriostatic effect on pathogenic microorganisms and increase product shelf life. In this research tarhana doughs were inoculated with pathogenic microorganisms Escherichia coli O157:H7, Staphylococcus aureus and E. coli O157:H7+S. aureus, separately. Tarhana samples were fermented at 35 +/- 2 degreesC for seven days, and dried using either a conventional hot air oven or a microwave oven. Counts of E. coli O157:H7, S. aureus, total mesophile aerobic bacteria, yeast-mould and lactic acid bacteria, as well as moisture and pH values were determined during fermentation and after drying. E. coli O157:H7 survived until the third day of fermentation in the inoculated samples; however it was not present after the fifth day. Counts of S. aureus decreased markedly after the first day of fermentation and were 10(2) cfu/g at the end of fermentation. Microwave drying completely destroyed the pathogen S. aureus, and was more efficient than the conventional method in reducing microbial population and moisture content of the samples.