Distinguishing the Disinfection Patterns of Listeria monocytogenes Contaminated Mozzarella Cheese by Using Gamma Irradiation Treatment

Abstract

In today’s world, food safety is a major concern, as many people throughout the world are becoming infected with foodborne pathogens; such as Listeriosis caused by Listeria monocytogenes, which is responsible for death of many children, pregnant women and aged people every year. In this study, the disinfection pattern of L. monocytogenes was examined on mozzarella cheese by using gamma irradiation. After bacterial inoculation (108 cfu/gm) into sterile (25 kGy) cheese our individual tasted strains as 6, 8, 13, 14, 15 were treated with irradiation doses as 1 kGy, 3 kGy, 5 kGy, 7 kGy, 9 kGy and 10 kGy with a highly pathogenic reference strain L. monocytogenes ATCC 7466. The initial bacterial range was 9.5 log10 cfu/gm to 7.9 log10 cfu/gm. Results of irradiation treatments showed that, when the radiation doses were increased as 1 kGy to 10 kGy, the number of colonies were significantly decreased at 3 to 7 logs respectively. But in the middle level, radiation doses such as 5kGy and 7 kGy showed near about similar ranges of deductions for every strain, which were 3.3 log10 cfu/gm to 3.0 log10 cfu/gm. The most effective radiation dose was 10 kGy, where most of the bacteria were killed in all strains. The threshold level of this L. monocytogenes is 2 log10 cfu/gm which is much higher than our results. According to “The International Atomic Energy Agency (IAEA)”, 10 kGy radiation dose is standard to disinfect foods. This study indicates that, L. monocytogenes can grow in prepared dairy foods like cheese, yogurt etc. but this can be potentially disinfected by using gamma irradiation processes for improving food safety of ready-to-eat foods.