whole_ChandlerRobertEdward1988_thesis.pdf (15.44 MB)
The effect of temperature and water activity on microbial growth rate and food spoilage
thesisposted on 2023-05-27, 06:33 authored by Chandler, Robert Edward
The Square Root Model [‚Äöv¿v¨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 ¬¨‚àû 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 ¬¨‚àû 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.
Rights statementCopyright 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). Thesis (Ph.D.)--University of Tasmania, 1989. Bibliography: p. 218-233