Refrigerated cucumber pickle products cannot be heat processed due to the loss of characteristic sensory attributes. Typically brined refrigerated pickles contain less than 100 mM acetic acid with pH values of 3.7 to 4.0. Refrigeration (4 to 10 °C) helps to inhibit the growth of spoilage bacteria and maintain flavor, texture, and appearance of the pickles. Previous research has shown that pathogenic Escherichia coli strains are unusually acid resistant and survive better in refrigerated acid solutions than at higher temperatures. We found that E. coli O157:H7 can survive for 1 mo or longer at 4 °C in brines typical of commercial refrigerated pickles. Our objective was to develop methods to assure a 5-log reduction of pathogenic E. coli in these types of products, while maintaining the sensory characteristics. A novel brine formulation was developed, based on current commercial refrigerated pickle brines, which contained 25 mM fumaric acid, 5 mM benzoic acid, 70 mM acetic acid, and 342 mM (2%) sodium chloride, with a pH of 3.8. Sensory data indicate that this formulation did not affect flavor or other sensory attributes of the product, compared to traditional formulations. We achieved a 5-log reduction of E. coli O157:H7 at 30 °C for 1.52 ± 0.15 d, at 20 °C for 3.12 ± 0.34 d, or at 10 °C for 8.83 ± 0.56 d. Growth of lactic acid bacteria was also inhibited. These results can be used by manufacturers to assure a 5-log reduction in cell numbers of E. coli O157:H7 and Salmonella without a heat process during the manufacture of refrigerated pickle products.
Practical Application: While refrigerated acidified vegetable products are exempt from the acidified foods regulations, we have shown that the vegetative microbial pathogens E. coli O157:H7 can survive for up to 1 mo in these products, given current commercial production practices. To improve the safety of refrigerated pickle products, a brine formulation with reduced acetic acid, but containing fumaric acid, was developed to assure a 5-log reduction in cell numbers of E. coli O157:H7 without a heat process. The formulation can be used to assure the safety of refrigerated pickled vegetables without altering sensory characteristics.