THE EFFECT OF STEP CHANGES IN SUCROSE CONCENTRATION ON THE GROWTH OF SALMONELLA-LYPHIMURIUM-LT2

Water activity is a method of preservation that can affect microbial g rowth in foods and that may fluctuate during their processing, distrib ution and storage. Sucrose has been used to change the water activity of microbiological culture media. Suspensions of Salmonella typhimuriu m LT2 in the exponential phase of growth have been subjected to step c hanges in sucrose concentration at 20 degrees C. The changes in the nu mbers of viable bacteria were measured with time and the experimental growth curves compared with predictions based on growth data obtained at constant sucrose concentrations. Steps down in sucrose concentratio n showed some apparent loss of viability after the step followed by gr owth at a rate close to the expected value. Steps up in sucrose concen tration resulted in a greater apparent loss of viability after the ste p and either growth or the inducement of lag, depending on the final c oncentration of sucrose. A series of small steps up in sucrose concent ration to 45% (w/v) was able to sustain growth where it was not possib le by inoculation directly into this concentration. Improved recovery of bacteria subject to osmotic stress was possible with a medium conta ining sodium chloride.