Tf. Brocklehurst et al., THE EFFECT OF TRANSIENT TEMPERATURES ON THE GROWTH OF SALMONELLA-TYPHIMURIUM LT2 IN GELATIN GEL, International journal of food microbiology, 27(1), 1995, pp. 45-60
The growth of colonies of Salmonella typhimurium derived from single i
mmobilised cells was studied while subjected to constant and sinusoida
lly-varying temperatures. The bacteria grew in microbiological culture
media adjusted to different pH and sodium chloride (NaCl) concentrati
on and solidified with gelatin that was contained within a cassette fo
rmed between sheets of PVC film that allowed gaseous exchange. At pH 7
.0 and 0.5% (w/v) NaCl and either 12 degrees C or 20 degrees C, S. typ
himurium grew at a rate similar to that in liquid medium. The decrease
in growth rate at 20 degrees C at a lower pH or higher NaCl concentra
tion was greater in the case of immobilised cells than for cells in li
quid medium. The change in the numbers of viable bacteria was measured
with time under sinusoidally-varying temperatures between 4 and 22 de
grees C and between 12 and 22 degrees C of period in the range 12 to 4
80 min. The experimental growth curves were compared with predictions
based on isothermal growth in liquid medium. The discrepancies between
experiment and prediction were greater for gels stressed by NaCl or p
H than for gels at pH 7.0 and containing 0.5% (w/v) NaCl, consistent w
ith the isothermal observations.