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Title: Independent effects of acetic acid and pH on survival of Escherichia coli in simulated acidified pickle products

item Breidt, Frederick
item Hayes, Janet
item McFeeters, Roger

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2003
Publication Date: 1/1/2004
Citation: Breidt, F., Hayes, J.S., McFeeters, R.F. 2004. Independent effects of acetic acid and pH on survival of Escherichia coli in simulated acidified pickle products. Journal of Food Protection. 67:12-18.

Interpretive Summary: We report on how efficiently components of pickle vegetable brines can kill selected strains of a pathogenic bacterium, Escherichia coli O157:H7. While other researchers have studied the effects of acids on the death rates of food pathogens, our research was unique in determining the relative effects of acidity (pH) and acid concentration. This is important because FDA regulations governing acidified foods (such as some types of pickled vegetables) are based only on the pH and not the acid concentration. We have demonstrated that the acetic acid concentration in many acidified foods can significantly enhance the killing of E. coli O157:H7. These results may help explain the historic safety of acidified pickle products, while other foods with a similar pH, but which lack acetic acid, have had outbreaks of food pathogens.

Technical Abstract: To determine the independent effects of organic acids and pH on the death kinetics of Escherichia coli we used gluconic acid as a non-inhibitory buffer. This was possible because we found that the inhibitory effects of this acid on selected E. coli strains at pH 3.1 were independent of acid concentration over a range of 2 mM to 200 mM. We, therefore, used gluconic acid at 20 mM concentration as a buffer to determine the effects of acetic acid, independent of pH, on the survival of E. coli, in conditions representative of acidified pickle products. Acetic acid (0.4 to 0.1 M) decreased D values 2- to 4-fold compared to the effect of pH for simulated brines ranging from pH 3.1 to 4.1. Glutamic acid, which is known to enhance acid resistance in E. coli and is a component of pickle brines, protected the E. coli strains from the specific effects of acetic acid.