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The effect of temperature and water activity on microbial growth rate and food spoilage

Chandler, Robert Edward 1988 , 'The effect of temperature and water activity on microbial growth rate and food spoilage', PhD thesis, University of Tasmania.

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The Square Root Model [✓r = b(T - T o )] was used to describe the
temperature dependence of bacterial growth rate under conditions
where temperature was the only limiting factor. It was validated for
predicting the growth of the bacteria responsible for the spoilage of
pasteurised, homogenised milk and for the in situ spoilage of the
milk, over the storage range 0 to I5 ° C.
A temperature function integrator, incorporating the Square Root
Model and a To value of 263K was successfully used to monitor the
temperature history of pasteurised, homogenised milk over a range of
storage temperatures and to display the cumulated storage history at
an arbitrary reference temperature (4 ° C).
The spoilage rate of pasteurised homogenised milk, with respect
to temperature, was described accurately by a Square Root Equation,
possessing a To value similar to that of the psychrotrophic
pseudomonads responsible for the spoilage of the milk.
The Square Root Model described the temperature dependent
variation in an induced bacterial lag phase, with the parameter, To
being similar to that of the exponentially growing cell.
The Square Root Model was shown to accurately predict bacterial
growth under conditions where both temperature and water activity
were limiting. Growth of the moderate halophile, Staphylococcus
xylosus strain CM21/3, in media of different water activities,
continued to be described by the Square Root Model, when either
sodium chloride or glycerol was used as the humectant. The parameter
To was constant, irrespective of water activity or the type of
humectant used. A decreasing linear relationship was demonstrated between growth
rate and decreasing water activity, with the minimum water activity
for growth being dependant upon humectant used. This enabled the
derivation of a modified Square Root Model, which was capable of
describing the effect of both temperature and water activity on
bacterial growth rate.
The Square Root Model was validated for predicting the growth of
the extreme halophiles, Halobacterium sp. strain HB9 and
Halobacterium salinarium strain CM42/12, under conditions of varying
water activity/salt concentration and temperature. The parameter To
was constant irrespective of water activity. In addition, little
change in growth rate, with change in water activity was noted.

Item Type: Thesis - PhD
Authors/Creators:Chandler, Robert Edward
Keywords: Food, Food spoilage, Food poisoning
Copyright Holders: The Author
Copyright Information:

Copyright 1998 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1989. Bibliography: p. 218-233

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