Effect of short-time microwave heating on survival of Escherichia coli O 157 in beef hamburgers

Abstract

Survival of three E scherichia coli strains O 157: B 032, LMG 8223, IVK 805 from the collection of the , in breaded and unbreaded beef hamburgers (n = 144), subjected to short microwave heating was determined. 50 g hamburger samples were contaminated by bacterial suspension injections (the initial contamination level was 10 6 cfu/g of product). Microwave heating for 30, 60, 90, 120 and 150 s was done using a microwave cooker (Dialog cook, Moulinex, at 480 and 760 W). 30 s heating at 480 W caused test bacteria cells partial reduction that wa s more pronounced in breaded hamburgers. In the case of E. coli O 157: B 032, the reduction was lower than for the other two strains. At 480 W , none of the E. coli O 157 test strains survived 60 s of heating that corre sponded to the hamburgers' temperature ranging from 75.2 to 89. 1°C. Increasing the power to 760 W, decrea sed the bacteria inactivation time to 30 s while the hamburgers' temperature ranged from 71.9 to 78.8°C. Indifferent of the cooker power for each of the heating times, breaded hamburgers achieved higher temperatures than the unbreaded ones.