The effect of heat treatment applied to the brine after packaging on the survival of Salmonella spp. and Listeria monocytogenes in traditional brined white cheese made from raw milk

In this study, post-production heat treatments were tried to ensure microbial food safety in brined white cheeses made from raw milk. The aim of the study is to investigate a heat treatment that will inactivate pathogens such as Salmonella spp. and Listeria monocytogenes while the brined white cheese is in brine, but will cause minimal damage to the natural flora and some quality parameters of the cheese. In each of the studies repeated three times, pathogens were inoculated were inoculated into the middle of cheese blocks prepared from raw milk and then dry salted. After adding 14% brine to the cheeses placed in one-liter glass jars, the jars were divided into four groups as control, S60, S70 and S80. Except for the control group S60, S70 and S80were placed individually in a 90-95°C hot water bath and heat treated until the brine temperatures reached the target (60°C, 70°C and 80°C) temperatures. During the heat treatment, both the brine temperatures and the core temperatures of the cheese blocks were monitored with a wire probe thermocouple. After the heat treatment, the cheese jars were stored at 7±1°C for 120 days, and microbiological (Salmonella spp., L. monocytogenes, Lactobacillus spp., lactic coccus, total aerobic mesophilic bacteria, Enterobacteriaceae spp. and yeast-mould) and chemical (pH, dry matter, salt and fat in dry matter) analyzes were performed on certain days. Additionally, pathogen-free cheese samples were prepared using the same method and subjected to sensory analysis at the end of the storage period. It was observed that the core temperature of the cheeses whose brine temperature was increased to 60°C increased to 49°C, and although this application reduced the Salmonella spp., L. monocytogenes, Enterobacteriaceae spp. and yeast-mold numbers compared to the control group (P<0.05), it wasn't sufficient in terms of food safety. It was determined that the cheese core temperatures in the S70 and S80 groups increased to 55.5 and 63.5°C, respectively, and that there was a significant decrease in Salmonella spp., L. monocytognes, Enterobacteriaceae spp. yeast-mold numbers compared to the control and S60 groups (P<0.05), and that microbial public health risks were eliminated within 15 days. Although the heat treatments in the S70 and S80 groups caused a significant decrease in the number of Lactobacillus spp. and lactic cocci compared to the control and S60 groups (P<0.05), it was observed that the numbers of these bacteria increased again during the storage period. When compared with the control group, it was determined that heat treatment in brine had no effect on the pH value of the cheese (P>0.05), and although there were differences compared to the control group in terms of dry matter, salt and fat values in dry matter on some days of storage (P<0.05), the differences disappeared at the end of the storage period. It was determined that S70 and S80 group cheeses received higher sensory scores than the control and S60 groups (P<0.05). As a result, it was concluded that in order to minimize or eliminate the microbial risks that may arise from both raw milk and the environment during the production process in brine cheese made from raw milk, it would be sufficient to apply heat treatment so that the core temperature of the cheese in 14% brine reaches at least 55.5°C.