Fourteen batches of cold-pack cheese food were contaminated with Salmonella typhimurium during manufacture. Cheese food stored at 4.4 and 12.8 C was tested at weekly intervals and salmonellae were enumerated by means of a Most Probable Number technique. A rapid decline in number of salmonellae occurred during the first week of storage regardless of temperature or composition of the product. Survival beyond this time was more closely related to both conditions. Viable salmonellae could not be recovered, after 3 weeks at 12.8 C or 5 weeks at 4.4 C, from cheese food adjusted to pH 5.0 with lactic acid and fortified with 0.24% potassium sorbate. Substituting sodium propionate for sorbate resulted in 14 and 16 weeks of survival by salmonellae when cheese food was held at 12.8 and 4.4 C, respectively. Partial or complete replacement of lactic acid by acetic acid was accompanied by somewhat longer survival of salmonellae than when only lactic acid was used. Elimination of added acid from the cheese food resulted in survival of salmonellae for 6 and 7 weeks when potassium sorbate was present, for 16 and 19 weeks when sodium propionate was used, and in excess of 27 weeks when no preservative was added.
1Published with the approval of the Director of the Research Division, College of Agricultural and Life Sciences, University of Wisconsin.