Graduate Thesis Or Dissertation
 

Experimental and mathematical procedures for the estimation of shelf-life : application to temperature-abused chilled seafood

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/c534fs466

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  • The validation and potential use of mathematical models to estimate the shelf-life of refrigerated food exposed to temperature abuse and basing such estimations on microbial growth was analyzed. Combined heat transfer, microbial growth models, and non-parametric statistical procedures formed a computer-based predictive tool to assess shelf-life and estimate the accuracy of the prediction. Experiments were carried out to assess the precision of the combined model parameters. The different situations analyzed considered stepwise fluctuations in environmental temperature and a change in package characteristic (size and packaging material). Computer simulations showed that even when the temperature abuse period constitutes a small fraction of the total exposure time (2%-3%), shelf-life can be highly affected (20%-30%). To analyze the precision of the combined model response, two sources of variation were considered, microbial growth and heat transfer parameters. First order, pseudo-zero order kinetics and Arrhenius model formed the basis for the microbial model. The accuracy of lag and exponential phase of microbial growth for a mixture of three microorganisms (P. fluorescens, S. aureus, and A. Iwoffi) was assessed using a nonparametric statistical procedure based on the bootstrap method. The activation energy (E [subscript a]) and the logarithm of the frequency factor (InK₀) were found to be 109±3.4 J/mole and 48.3±1.5 for the exponential phase of this microbial mixture. The values for the exponential phase were 152±4 J/mole and 64.0±1.7, respectively. These parameters together with experimental values for the overall heat transfer coefficient were used to analyze the precision of the model response. This precision was not affected by a change in environmental temperature and packaging characteristics and remained constant at ±1 day. Two different temperature abuse situations yield estimated shelf-life of 4.8±1 and 8.9±1 day, respectively. This result can not be generalized as it depends on the particular examples analyzed.
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