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Food Safety Works Colorado State University Extension
SafeFood Rapid Response Network

SAFEFOOD NEWS - Summer 1998 - Vol 2 / No. 4

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Slow Cooking May Induce Heat Resistance in E. coli

Escherichia coli 0157:H7 bacteria can become more heat resistant when exposed to a sublethal dose of heat. Scientists from the Agricultural Research Service (ARS) in Wyndmoor, Pennsylvania, say this finding reiterates the continuing need to adequately cook food to kill E. coli 0157:H7. Cooking remains the primary means to kill E. coli.

Vijay K. Juneja and colleagues, from the ARS Eastern Regional Research Center (ERRC), subjected beef gravy samples containing E. coli 0157:H7 to 114.8 F. for 15 to 30 minutes. This heat-shocked the bacteria at a temperature not quite sufficient to kill them. Then the researchers cooked the gravy to a final internal temperature of 140 F.

The pre-heated E. coli survived longer than other E. coli not subjected to the sublethal heat. The increased thermotolerance lasted for at least 48 hours. Juneja states that food processors should realize that some E.coli bacteria will not be killed in foods that are heated slowly to the final cooking temperatures normally used. Heat-shocking conditions may occur in minimally processed, refrigerated, cook-in-bag foods such as filled pasta products (ravioli, tortellini, canneloni, etc.), mousaka, lasagna, and chili con carne. The slow heating rate and low heating temperatures used in preparing these foods expose potential pathogens to conditions similar to heat shock, which could make them more heat-resistant.

Induced heat-resistance could also be a concern in meat products kept on warming trays before final heating or re-heating, or when equipment failure interrupts the cooking cycle during processing.

Source: Agricultural Research, July 1998.

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Updated Monday, August 29, 2011