Thermal inactivation of Listeria monocytogenes during rapid and slow heating in sous vide cooked beef

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Heating at slowly rising temperatures is suspected to enhance thermotolerance in Listeria monocytogenes and, since anaerobic environments have been shown to facilitate resuscitation of heat-injured cells of this micro-organism, concern may arise about the possibility of L. monocytogenes surviving in minimally preserved products. The effect of rapid ( > 10°C min-1) and slow (0.3 and 0.6°C min-1) heating on survival of L. monocytogenes in sous vide cooked beef was therefore examined at mild processing temperatures of 56°, 60° and 64°C. No statistically significant difference (P=0.70) was observed between the tested heating regimes. Since the average pH of beef was low (5.6), and little or no effect was observed, a pH-dependency of heat shock-induced thermotolerance in L. monocytogenes is suggested to account for this result.

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