Evaluation of the antimicrobial effect of sodium chloride on Escherichia coli O157:H7 and Staphylococcus aureus in a laboratory medium and on beef briskets with investigation of the koshering process

Salt (sodium chloride, NaCl) has been in use, historically, as an additive and preservative in foods, and it is currently an inexpensive product. As a surface application to fresh meat, salt mainly is used by the koshering industry as a ritual practice for removing blood from meat trimmings, but not for decontamination of meat surface. This dissertation evaluates the effectiveness of the overall koshering process and its sub-processes (water soaking, salting, and water rinsing) in reducing Escherichia coli O157:H7 and Staphylococcus aureus counts. To accomplish this major objective, this research was divided into three interrelated studies. First, the antimicrobial effect of five commercial NaCl grades on E. coli O157:H7 and S. aureus aerobically grown in Brain Heart Infusion (BHI) was investigated. Growth curves for variety of salt types, concentrations, exposure times, and recovery media were generated for characterizing the salt dynamics against the two pathogens. Second, the effect of NaCl grade and concentration on type and magnitude of morphological cellular damage was determined using transmission electron microscopy (TEM). Third, laboratory-scale simulations of koshering process were conducted to assess its effectiveness in removal of E. coli O157:H7and S. aureus inoculated on fresh beef briskets. The water soaking, salting, and water rinsing sub-processes were simulated under varying conditions, and their relative contribution to the overall koshering process performance was determined. In an attempt to improve the salting sub-process, highly concentrated NaCl solution (25%) was sprayed for prespecifed durations on meat surfaces inoculated with E. coli O157:H7and S. aureus. Acidified sodium chlorite (ASC); a commercially used antimicrobial solution, also was employed and performance compared to that of NaCl solution and plain water wash (WW).; Results of growth curves indicated increased bacterial inhibition with increasing salt concentration, and S. aureus had relatively higher tolerance to salt compared to E. coli O157:H7. TEM results qualitatively confirmed the findings from growth curves experiments, and unlike E. coli O157:H7, S. aureus cells nearly maintained their cellular structure. The koshering process reduced E. coli O157:H7 and S. aureus nearly equally by 0.91 and 0.94 logs₁₀ (i.e., ∼88 and 89% removal), respectively, with the salting sub-process primarily contributing to E. coli O157:H7 reduction and the water rinsing to S. aureus. Optimizing the koshering process can result in a validated 1 log₁₀ in E. coli O157:H7 WW, NaCl, and ASC reduced bacterial counts compared to the controls, and generally ASC outperformed both NaCl and WW.