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Prajapat, Vandanna Devi (2004) Predictive modelling of food spoilage using volatile metabolite accumulation as a measure of growth. Doctoral thesis, London Metropolitan University.
The previous and present-day technologies employed in predictive microbiology and qualitative and quantitative chemical analysis of microbial metabolites were investigated, with a view to application in the development of spoilage models using volatile microbial metabolite accumulation as a measure of growth.
A novel method was developed, which enabled the detection and identification of volatile metabolites, and was applied to two groups of food spoilage organisms: Br. thermosphacta and Pseudomonas and related genera. Solid phase microextraction combined with both a gas-liquid chromatograph/flame ionisation detector and a gas-liquid chromatograph/mass spectrometer were applied to the analysis of volatile metabolites produced by these spoilage organisms.
Specifically, a model was developed for Br. thermosphacta in microbial media using the accumulation of 3-methyl butanol (3-M-B) under differing conditions of pH (4.5-7.5), aw [0.5-7.5% (ʷ/ᵥ)] and incubation temperature (2-10°C). This model was verified and validated in minced beef. The transferability of the method to the development of models for other spoilage organisms was investigated by studying volatile metabolites accumulated in microbial media inoculated with Pseudomonas and related genera under the same range of environmental conditions.
Several differences were observed between the total viable cell count technique normally used for data collection for predictive microbiology and the quantification of metabolites. The major difference was that, unlike total viable cell count data, which could be monitored from the beginning of the experiment, volatile metabolites did not accumulate until late exponential phase or early stationary phase of growth. Further studies into the lag phase, effect of physical structure of the environment, effect of extreme and optimum conditions on volatile metabolite accumulation and analytical conditions may in future, resolve some of the issues impeding the development of more robust models based on volatile metabolite accumulation.
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