THERMAL INACTIVATION OF LISTERIA-MONOCYTOGENES DURING RAPID AND SLOW HEATING IN SOUS VIDE COOKED BEEF

Heating at slowly rising temperatures is suspected to enhance thermoto lerance in Listeria monocytogenes and, since anaerobic environments ha ve been shown to facilitate resuscitation of heat-injured cells of thi s micro-organism, concern may arise about the possibility of L. monocy togenes surviving in minimally preserved products. The effect of rapid (> 10 degrees C min(-1)) and slow (0.3 and 0.6 degrees C min(-1)) hea ting on survival of L. monocytogenes in sous vide cooked beef was ther efore examined at mild processing temperatures of 56 degrees, 60 degre es and l64 degrees C. No statistically significant difference (P = 0.7 0) was observed between the tested heating regimes. Since the average pH of beef nias low (56), and little or no effect was observed, a pH-d ependency of heat shock-induced thermotolerance in L. monocytogenes is suggested to account for this result.