Abstract 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. Or- ganic acid production during the fermentation and low- ering 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 microorgan- isms Escherichia coli O157:H7, Staphylococcus aureus and E. coli O157:H7+S. aureus, separately. Tarhana samples were fermented at 35±2 °C 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 effi- cient than the conventional method in reducing micro- bial population and moisture content of the samples. Keywords Tarhana · E. coli O157:H7 · S. aureus · Fermentation · Drying Introduction Fermentation is the oldest known form of food biotech- nology and fermented foods contribute to about one- third of the diet worldwide. They are particularly impor- tant as weaning foods for infants and as dietary staples for adults. The technology of producing many indige- nous fermented foods from cereals remains a household art in these countries [1, 2]. As a fermented product tarhana is the dry form of yoghurt-cereal mixture and forms an important part of the diets of many people in Turkey [3, 4, 5]. It is pre- pared by mixing wheat flour, yoghurt, yeast and a variety of cooked vegetables (tomatoes, onions, green pepper etc.), salt and spices (mint, paprika) followed by fermen- tation for one to seven days. In some places one or more of those ingredients such as milk, soybean, lentil, chick- pea, corn flour and egg are also added [5, 6, 7, 8]. The temperature of fermentation is in the range of 30–40 °C depending on the procedure applied. The product is sun dried in home made tarhana and oven dried in commer- cial production to a moisture content of 6–10%. Follow- ing the drying procedure, tarhana is ground to particle size of <800 μm [9, 10]. Throughout fermentation lactic acid bacteria (Strepto- coccus thermophilus, Lactococcus lactis, Lactococcus di- acetylactis, Lactobacillus bulgaricus, Lactobacillus aci- dophilus, Leuconostoc cremoris, Lactobacillus casei) and yeast (Saccharomyces cerevisiae) give the characteristic taste and flavour of tarhana by producing lactic acid, ethanol, carbon dioxide and some other organic com- pounds. Organic acids formed during fermentation period lower the pH and after fermentation excess moisture is removed by drying. Final product with low pH (3.8–4.2) and low moisture content (6–10%) is a poor medium for pathogens and spoilage organisms [9, 11, 12]. Bacterial pathogens play a major role in outbreaks of foodborne diseases and among these pathogens Escheri- chia coli O157:H7 and Staphylococcus aureus are recog- nized as important human pathogens. A very wide range of foods including raw materials, milk and dairy prod- ucts, cooked meats, poultry and vegetables have been shown to contain these pathogens. Outbreaks of food- borne illness by E. coli O157:H7 and Staphylococcus aureus are often associated with inadequate sanitary handling and holding the food at an inappropriate tem- perature for a prolonged period, thus allowing growth of the pathogens [13, 14, 15, 16]. O. Daglioglu ( ✉ ) · M. Arici · M. Konyali · T. Gumus Trakya University, Tekirdag Agricultural Faculty, Department of Food Engineering, 59030 Tekirdag, Turkey e-mail: odaglioglu@tu.tzf.edu.tr Eur Food Res Technol (2002) 215:515–519 DOI 10.1007/s00217-002-0584-0 ORIGINAL PAPER Orhan Daglioglu · Muhammet Arici · Murat Konyali Tuncay Gumus Effects of tarhana fermentation and drying methods on the fate of Escherichia coli O157:H7 and Staphylococcus aureus Received: 8 April 2002 / Revised: 24 June 2002 / Published online: 21 August 2002 © Springer-Verlag 2002