Mechanisms of heat inactivation in Salmonella serotype Typhimurium as affected by low water activity at different temperatures.
OBJECTIVE
To determine the effect of reduced water activity (a(w)) on thermal inactivation of Salmonella serotype Typhimurium at different temperatures and its mechanism.


RESULTS
D-value determinations at a range of different temperatures showed that heating at reduced a(w) (0.94, produced by addition of glucose or sodium chloride to nutrient broth) was protective at temperatures above 53-55 degrees C but sensitizing below this temperature. Using selective enumeration media to determine injury, it was shown that at lower heating temperatures cells survived at high a(w) with cytoplasmic injury whereas at low a(w) these cells were killed. At higher temperatures ribosome degradation was a more important cause of death and was inhibited by low a(w) heating media thereby providing greater heat resistance.


CONCLUSIONS
The observed change in behaviour reflects the different reactions responsible for thermal death at different temperatures and their different response to reduced a(w).


CONCLUSIONS
This work qualifies the previous assumption that reduced a(w) is protective and suggests that the efficacy of low temperature pasteurization regimes may be increased by reduced a(w).
Aljarallah
K M
KM
School of Biomedical and Molecular Sciences, University of Surrey, Guildford, Surrey, UK.
Adams
M R
MR
D015169:Colony Count, Microbial; D003470:Culture Media; D005516:Food Microbiology / Q000592:standards; D005519:Food Preservation / Q000379:methods; D005947:Glucose / Q000378:metabolism; D006358:Hot Temperature; D008274:Magnesium / Q000378:metabolism; D012329:RNA, Bacterial / Q000032:analysis; D012335:RNA, Ribosomal / Q000032:analysis; D012486:Salmonella typhimurium / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D012965:Sodium Chloride / Q000378:metabolism; D014867:Water
D003470:Culture Media; D012329:RNA, Bacterial; D012335:RNA, Ribosomal; D014867:Water; D012965:Sodium Chloride; D008274:Magnesium; D005947:Glucose