The influence of the formulation. cooking time and final internal temperature of beef hamburgers on the destruction of Listeria monocytogenes was evaluated. Four hamburger formulations: 10% fat (F1), 20% fat (F2), 10% fat and 1.5% sodium chloride (F3) and 10% fat and 10.5% hydrated texturized soy protein (F4) were inoculated with a mixture of five strains of L. monocytogenes, Frozen hamburgers were cooked on a preheated electric griddle for 2, 4, 6, 8 and 10 min. Following removal from the griddle, hamburgers were held at room temperature for 1 min to Simulate the time elapsed between cooking and consumption in commercial establishments, or they were immediately cooled. The results showed that the addition of 10.5% hydrated texturized protein had no effect on the lethality of the cooking process. However, the addition of 1.5% NaCl protected the bacterial cell against heat destruction. No conclusion could be made with respect to the effect of the increase in fat content (10-20%) in the meat. It was also shown that the increase in heating time and the additional '1-min period' at room temperature increased the lethality of the cooking process. Moreover, the results revealed a wide variability in the internal temperature of beef hamburgers at the end of cooking. These results revealed that control of the cooking process by the final internal temperature of hamburgers can be insufficient to ensure a safe product. (C) 2001 Elsevier Science Ltd. All rights reserved.1313340