Effect of storage time and temperature on the viability of E. coli O157:H7, Salmonella spp., Listeria innocua, Staphylococcus aureus, and Clostridium sporogenes vegetative cells and spores in vacuum-packed canned pasteurized milk cheese

The effect of storage temperature and time on the viability of several foodborne bacterial pathogens inoculated into vacuum-packed canned pasteurized cow's milk cheese was investigated. Three popular cheese styles namely, a semi-soft white Monterey Jack style cheese, and two Cheddar cheeses vacuum packaged in mason jars were inoculated with a 3-strain cocktail of each of the following microbes at the mean concentrations listed: Escherichia coli O157:H7 (6.6 log CFU/g), Salmonella spp. (6.3 log CFU/g), Listeria innocua (6.4 log CFU/g), Staphylococcus aureus (3.6 log CFU/g), and Clostridium sporogenes vegetative cells (6.3 log CFU/g), and spores (6.0 log CFU/g). The effect of storage temperature (at 4.4, 10, and 21.1 °C) and the time (from 0 to 365 days) on the survival of the inoculated organisms was evaluated at different sampling times (0, 30, 60, 120,180, and 365 days). Both storage temperature and the time had a significant effect on the viability of the test organisms. Increasing the storage temperature from 4.4 to 21.1 °C and the storage time for up to 365 days increased pathogen reduction. The type of cheese also had a significant effect on the viability of the test organisms. At the same sampling times, the viability of E. coli O157:H7 and Salmonella spp., were highest in Monterey Jack-style cheese followed by the Cheddar cheeses one to which annatto had been added (Cheddar 1) and the second, a white Cheddar that has an added adjunct flavor culture (Cheddar 2). Similarly, the type of cheese and the time-temperature conditions to which the cheese was exposed had a significant effect on the viability of L. innocua. Among the tested organisms, S. aureus was most susceptible while C. sporogenes (both vegetative cells and spores) were most resistant. The findings of this challenge study indicate that vacuum packed canned cheese is not a favorable environment for the growth of bacterial pathogens. Depending upon the type of canned cheese, appropriate storage times and temperatures are critical to ensure microbiological safety.