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The Effect of Temperature and Water Activity on Microbial Growth Rate and Food Spoilage

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The Effect of Temperature and Water Activity on Microbial Growth Rate and Food Spoilage THE EFFECT OF TEMPERATURE AND WATER ACTIVITY ON MICROBIAL GROWTH RATE AND FOOD SPOILAGE. Robert Edward Chandler, B.Sc.(Hons.), Being a thesis in fulfilment of the requirements for the degree of Doctor of Philosophy (Microbiology), at the University of Tasmania. University of Tasmania, Hobart, Tasmania, Australia, January,H988... 7),24.0 Cksc), b coN6LER_ VCVA THE UNIVERSITY OF TASMANIA LiBRARY DECLARATION. This thesis contains no material which has been accepted for the award of any other degree or diploma in any University, and to the best of my knowledge contains no copy or paraphrase of material previously published or written by any other person, except where due reference is made in the text of this thesis. Robert Edward Chandler, University of Tasmania, Hobart, Tasmania, Australia, January, 1988. iii ABSTRACT. 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 T value of 263K was successfully used to monitor the o 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 T value similar to that of the psychrotrophic o 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, T o 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 T was constant, irrespective of water activity or the type of o humectant used. iv 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 T o was constant irrespective of water activity. In addition, little change in growth rate, with change in water activity was noted. TABLE OF CONTENTS. PAGE. TITLE DECLARATION. ii ABSTRACT. TABLE OF CONTENTS. LIST OF FIGURES. vi LIST OF TABLES. LIST OF COMMONLY USED ABBREVIATIONS. xiii PUBLICATIONS. xv ACKNOWLEDGEMENTS. xvi 1: LITERATURE REVIEW. 1 2: MATERIALS AND METHODS. 48 3: RESULTS AND DISCUSSION. 71 4: CONCLUSIONS AND PROJECTIONS. 214 5: BIBLIOGRAPHY. 218 6: APPENDICES. 234 vi LIST OF FIGURES. FIGURE PAGES 1.1: Arrhenius plots of five bacteria and a fungus. 7-8 1.2: Square root of growth rate versus temperature for Pseudomonas sp. strain 16L16. 10-11 1.3: Square root of growth rate versus temperature for nine bacterial cultures. 13-14 1.4: Relation between mean growth rate and water activity for 14 strains of Staphylococcus aureus. 23-24 1.5: Mathematical relationships between temperature and spoilage constants. 33-34 2.1a: Diagnostic key for the identification of certain Gram- negative isolates. 54 2.1b: Diagnostic key for the identification of certain Gram positive isolates. 55 3.1: Plot of carbon dioxide concentrations versus microbial numbers. 79-80 3.2: Square root plots of the effect of temperature on the spoilage of pasteurised, homogenised milk. 81-82 3.3: Square root plots of the effect of temperature on the spoilage of pasteurised, homogenised milk. 84-85 3.4: Square root plots of the effect of temperature on the spoilage of pasteurised, homogenised milk. 86-87 3.5: Square root plots of the effect of temperature on the spoilage of pasteurised, homogenised milk. 88-89 3.6: Square root plots of the effect of temperature on the spoilage of pasteurised, homogenised milk. 90-91 3.7: Plots of microbial and pseudomonad numbers versus time/ temperature function integrator readings. 104-105 3.8: Nephelometer calibration curves for Pseudomonas sp. strain E5.2. 116-117 3.9: Square root plots of the effect of temperature on the growth rates of Enterobacter agglomerans strain 11.33 and Pseudomonas sp. strain 12.48. 119-120 vii 3.10: Comparison of the square root plots of the effect of temperature on the growth rates of Enterobacter agglomerans strain 11.33 and Pseudomonas sp. strain 12.48. 122-123 3.11: Square root plots of the effect of temperature on the growth rate and lag phase of Pseudomonas sp. strain E5.2. 127-128 3.12: Square root plots of the effect of temperature on the growth rate and lag phase of Pseudomonas sp. strain E5.2. 129-130 3.13: Square root plots of the effect of temperature on the lag phase of Pseudomonas sp. strain E5.2. 134-135 3.14: Nephelometer calibration curves for Staphylococcus xylosus strain CM21/3. 137-138 3.15: Square root plots of the effect of temperature and sodium chloride concentration on the growth rate of Staphylococcus xylosus strain CM21/3. 141-142 3.16: Square root plots of the effect of temperature and sodium chloride concentration on the growth rate of Staphylococcus xylosus strain CM21/3. 143-144 3.17: Square root plots of the effect of temperature and sodium chloride concentration on the growth rate of Staphylococcus xylosus strain CM21/3. 145-146 3.18: Square root plots of the effect of temperature and sodium chloride concentration on the growth rate of Staphylococcus xylosus strain CM21/3. 147-148 3.19: Square root plots of the effect . of temperature and sodium chloride concentration on the growth rate of Staphylococcus xylosus strain CM21/3. 149-150 3.20: Square root plots of the effect of temperature and sodium chloride concentration/water activity on the growth rate of Staphylococcus xylosus strain CM21/3. 154-155 2 3.21: A plot of the value of b associated with different sodium chloride/water activity levels for Staphylococcus xylosus strain 0421/3. 159-160 3.22: Square root plots of the effect of temperature and glycerol concentration on the growth rate of Staphylococcus xylosus strain 0421/3. 163-164 viii 3.23: Square root plots of the effect of temperature and glycerol concentration on the growth rate of Staphylococcus xylosus strain CM21/3. 165-166 3.24: Square root plots of the effect of temperature and glycerol concentration/water activity on the growth rate of Staphylococcus xylosus strain CM21/3. 169-170 2 3.25: A plot of the value of b associated with different glycerol/water activity levels for Staphylococcus xylosus strain CM21/3. 171-172 3.26: Nephelometer Calibration Curves for Halobacterium sp. Strain HB9 and Halobacterium salinarium Strain M42/12. 178-179 3.27: Square Root Plots of the Effect of Temperature and Sodium Chloride Concentration on the Growth Rate of Halobacterium sp. Strain HB9. 182-183 3.28: Square Root Plots of the Effect of Temperature and Sodium Chloride Concentration on the Growth Rate of Halobacterium sp. Strain HB9. 184-185 3.29: Square Root Plots of the Effect of Temperature and Sodium Chloride Concentration on the Growth Rate of Halobacterium sp. Strain HB9. 186-187 3.30: Square Root Plots of the Effect of Temperature and Sodium Chloride Concentration on the Growth Rate of Halobacterium sp. Strain HB9. 188-189 3.31: Square Root Plot of the Effect of Temperature and Sodium Chloride Concentration on the Growth Rate of Halobacterium sp. Strain HB9. 190-191 3.32: Square Root Plots of the Effect of Temperature and Sodium Chloride Concentration/Water Activity on the Growth Rate of Halobacterium sp. Strain HB9. 196-197 3.33: Square Root Plots of the Effect of Temperature and Sodium Chloride Concentration on the Growth Rate of Halobacterium salinarium Strain CM42/12. 200-201 3.34: Square Root Plots of the Effect of Temperature and Sodium Chloride Concentration on the Growth Rate of Halobacterium salinarium Strain CM42/12. 202-203 3.35: Square Root Plots of the Effect of Temperature and Sodium Chloride Concentration on the Growth Rate of Halobacterium salinarium Strain C442/12. 204-205 ix 3.36: Square Root Plots of the Effect of Temperature and Sodium Chloride Concentration/Water Activity on the Growth Rate of Halobacterium salinarium Strain CM42/12. 2 10-2 11 LIST OF TABLES. TABLE PAGE 1.1: Water activity, water content and the microbial spoilage of some foods. 21 1.2: Categories of methods for the evaluation of spoilage. 29 1.3: T values for various bacteria. 38 1.4: Comparison of relative rates of spoilage as predicted by the 011ey/Ratkowsky curve, the Square Root Model and experimental data. 41 1.5: The effect of temperature and initial number of psychrotrophic bacteria on the shelf-life of poultry carcasses. 45 2.1: Tests used to characterise bacterial isolates. 53 2.2: Water activities of moderate halophile broths containing different sodium chloride concentrations.
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