Tf. Brocklehurst et al., THE EFFECT OF STEP CHANGES IN SUCROSE CONCENTRATION ON THE GROWTH OF SALMONELLA-LYPHIMURIUM-LT2, Journal of Applied Bacteriology, 78(5), 1995, pp. 495-500
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.