Impact of low-dose gamma irradiation treatment on microbial and chemical properties of raw milk white cheese

Abstract

Using raw milk in cheese-making has microbiological risks, however a considerable number of artisan cheese makers around the world prefer raw milk, as heat treatment damages natural microbiota and alters the characteristic taste and flavor of the cheese. The potential of the gamma irradiation process to make the raw milk cheese microbiologically safe was investigated in this study. A total of 5 groups of cheese were produced, including control groups (control pasteurized milk cheese and control non-irradiated raw milk cheese). After the white cheese samples were kept in brine for 1 night, they were vacuum-packaged and each group was subjected to gamma irradiation at doses of 1, 2, and 3 kGy, respectively. Chemical composition, pH, acidity, Urea-PAGE images, total aerobic mesophilic bacteria (TAMB), coliform group bacteria, E. coli, yeasts and molds, Lactobacillus and Lactococcus counts of cheese samples were determined during 60 days of storage at 4°C. All analyzes were performed on days 1, 30, and 60 of production. We found that irradiation reduced the microbiological load of the cheeses and slowed down the degradation of αs1-CN and β-CN especially at 3 kGy. Irradiation at 3 kGy successfully inhibited the coliforms and E. coli, however yeast and mold counts were still high due to initial high levels. Our study showed that irradiation of the raw milk cheese is a promising method to reduce the microbial counts to acceptable limits which could reduce the required ripening periods for the microbial safety of raw milk cheeses.