Minimum inhibitory concentration (MIC) of sodium lactate and sodium chloride for spoilage organisms and pathogens at different pH values and temperatures

A selection of food spoilage organisms and pathogens were screened for sensitivity towards sodium lactate. The effect of pH (5.7 to 7.0) and temperature (4 to 37 degrees C) on the minimum inhibitory concentration (MIG) was determined in a peptone-yeast extract medium. NaCl was used as a reference to distinguish between the effect of water activity (a(w)) and the specific inhibitory effect of sodium lactate. In general, if MIC values of sodium lactate decreased at low temperature, those of NaCl decreased as well. Compared to NaCl, much lower molar concentrations of sodium lactate were needed to prevent growth. For most of the bacteria, MIC values of sodium lactate strongly decreased at low pH values. Ar pH 5.7, the presence of sodium lactate (greater than or equal to 268 mM) often did not allow growth. However, for Staphylococcus aureus, Lactococcus cremoris, Lactococcus lactis and some lactic acid bacteria isolated from spoiled meat products, the MIC value of sodium lactate did not change with pH. These organisms were relatively strongly inhibited by sodium lactate at high pH (7.0). Yeasts were less sensitive to sodium lactate than the bacteria, In most cases, MIC values of sodium lactate for Debaryomyces hansenii, Candida zeylanoides, and Zygosaccharomyces bailii exceeded the highest concentration used for screening (1,339 mM), independent of the pH of the growth medium. Rhodotorula mucilaginosa was more sensitive, the MIC value of sodium lactate being about 893 mM. MIC values of NaCl appeared to be independent of the pH in the range 5.7 to 7.0 for all microorganisms that were screened.