Abstract

Survival of three Escherichia coli strains O 157: B 032, LMG 8223, IVK 805 from the collection of the Department of Veterinary Protection of Public Health, Faculty of Veterinary Medicine, University of Gent, Belgium, 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 106 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 was 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 corresponded to the hamburgers’ temperature ranging from 75.2 to 89.1°C. Increasing the power to 760 W, decreased 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.

Key words: E. coli O 157, inactivation, microwaves, beef hamburgers