Control of B. cereus spores in egg white

At the Department of Food Science at the University of Otago, we are finding ways to control the germination of B. cereus spores in heat sensitive foods such as egg white. A paper on this topic entitled “Impact of temperature, nutrients, pH and cold storage on the germination, growth and resistance of Bacillus cereus spores in egg white” by Ms Aswathi Soni, Mr Pat Silcock and Professors Indrawati Oey and Phil Bremer, was recently published in the journal Food Research International. This paper demonstrated that egg white is not a favorable media for germination but the presence of egg yolk, which can occur as a contaminant from the separation of egg white and yolk, enhances germination. Storing the spores at 4 °C or below prevented germination as did reducing the pH of egg white below 4. Interestingly, using a model food system, it was found that the thermal resistance of the spores decreased during storage at 4 °C. Validating this result, in a real food system, may help in the development of strategies to reduce the degree of heating required to inactivate spores. Currently we are investigating the genetic and physical changes occurring in the spores associated with the decrease in their thermal resistance during cold storage.

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