Radiation sensitivity of selected pathogens in ice cream

Microbial contamination was investigated using ice creams with a vanilla, chocolate, and strawberry flavor commercially available in Korea. Radiation sensitivity of the food-borne pathogens was also determined by an inoculation test. Food-borne pathogens used were Listeria ivanovii, Escherichia coli, and Salmonella typhimurium. Total aerobic bacteria, moulds and yeasts, and coliforms in the ice creams ranged from 2 to 3 log CFU/g. Irradiation of 3 kGy was enough to inactivate the total aerobic bacteria for the vanilla ice cream but that of 5 kGy was needed for the chocolate or strawberry ice creams at a frozen condition (−20 °C). To inactivate (>log 6.5) the inoculated L. ivanovii, E. coli, and S. typhimurium into ice cream irradiation of 3, 1, and 0.1 kGy was needed, respectively. The D10 value of L. ivanovii and E. coli was calculated as 0.71-0.77 and 0.28-0.38 kGy range for the ice cream with different flavors at −72 °C, respectively. The D10 value of S. typhimurium could not be calculated in this study because even 0.1 kGy of irradiation reduced the number of S. typhimurium to undetected level. Results suggest that a low dose irradiation can improve the microbial quality and reduce the risk by the food-borne pathogens of ice cream, which has limited alternative sterilization methods due to the temperature characteristics of the products.