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Relationship between the apparent heat resistance of Bacillus cereus spores and the pH and NaCl concentration of the recovery medium

Abstract : Conventional heat resistance data , D values, were previously established by other workers at optimal condition for spores outgrowth. However, in canned food conditions of outgrowth are generally suboptimal in term of pH, salt concentration, water activity. Counts of survival spores after heat treatment are greatly influenced by the characteristics of the recovery medium. The selectivity of incubation conditions is enhanced by the injury of cells at sub-optimum recovery conditions. Both a decrease of number of viable cells being able to producing colonies and a decrease of the decimal reduction time is observed. The combined effects of pH and NaCl level of the recovery medium for the D value and ZpH value were studied. Spores of Bacillus cereus were heated at 95°C in phospho-citric buffer media at pH7. Cells were recovered at 25°C in nutritive agar with pH ranging from 5 to 7 and 1% to 4% NaCl concentration. For each condition D' values ( decimal reduction time associated with the recovery media characteristics) were determined. The results show a main influence of the recovery pH on the D' values. This effect is characterised by the z'pH values, distance of recovery medium pH from optimum recovery pH* medium (6.7) which leads to ten fold reduction time of D-value. The increase of the salt concentration leads to a slight decrease of D' value. However z'pH values are not significantly affected by the salt concentration. A simple three parameter model describing the effects of pH and NaCl concentration of the recovery medium upon the heat resistance of spores is proposed The interaction between pH and salt concentration is sufficiently low to be neglected by the model.
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https://hal.univ-brest.fr/hal-00654218
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Submitted on : Wednesday, December 21, 2011 - 11:44:12 AM
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Ivan Leguérinel, Olivier Couvert, Pierre Mafart. Relationship between the apparent heat resistance of Bacillus cereus spores and the pH and NaCl concentration of the recovery medium. International Journal of Food Microbiology, Elsevier, 2000, pp.223-227. ⟨hal-00654218⟩

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