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. / Graduation date: 1993
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27097 |
| Date | 24 August 1992 |
| Creators | Almonacid-Merino, Sergio Felipe |
| Contributors | Torres, J. Antonio |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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