Purpose: The purpose of the this study was to determine the relative effects of temperature, acetic acid and benzoic acid concentration on 5-log reduction times for EHEC under conditions typical of acidified vegetables.
Methods: A cocktail of 5 E. coli O157:H7 strains was subjected to 1% and 2% acetic acid solutions, with and without 0.1% benzoic acid at 10, 20, and 30°C under anaerobic conditions at pH 3.5 using brined cucumbers as a representative pickled vegetable. Surviving cells were recovered on non-selective tryptic soy agar at 37°C for 48 h. Survivor curves from 3 or more independent replications were analyzed with SAS (PROC MIXED) and Matlab software to determine and compare 5-log reduction times.
Results: For 2% acetic acid data, increasing temperature (10°, 20°, and 30°C) resulted in a 10-fold decrease in 5-log reduction times with and without benzoate. The 5-log reduction time with 0.1% benzoate at 10°C was 73 ± 5 hours vs 8 ± 0.22 h at 30°C, and similarly, 328 ± 12.5 hours vs 28.6 ± 0.9 hours without benzoate. For 20 and 30°C data, the interactions of the effect of benzoate temperature or acetic acid on the 5-log reduction times were found to be significant (P < 0.05).
Significance: The data show the importance of benzoate and increasing temperature for decreasing 5-log reduction times for pathogenic E. coli strains in acidified vegetable products. Results may be useful for estimating 5-log reduction times based on product formulation and storage conditions.