the handbook of food engineering practice crc press chapter 10 ...

analysis of the system of differential equations. These parameters can be used to predict
the concentration of each degradation product as a function of time at any temperature.
10.2.2.EFFECT OF ENVIRONMENTAL FACTORS
10.2.2.1 Temperature
The hitherto outlined approaches to kinetically define a food system include
the underlying assumption that the environmental conditions are constant. A shelf life loss
kinetic model is characteristic not only of the studied food but equally impotantly to the set
of environmental conditions of the experiment. These conditions can determine the reaction
rates and have to be defined and monitored during kinetic experiments.
Since most enviromental factors do not remain constant the next logical step
would be to expand the models to include them as variables, especially the ones that more
strongly affect the reaction rates and are more prone to variations during the life of the
food. The practical approach is to model the effect into the apparent reaction rate constant,
i.e. expressing k of eq. (9) as a function of E j : k =k(E j ).
Of the aforementioned environmental factors namely temperature, relative
humidity, total pressure and partial pressure of different gases, light and mechanical
stresses, the factor most often considered and studied is temperature. This is justifiable
because temperature not only strongly affects reaction rates but is also directly imposed to
the food externally (direct effect of the environment), the other factors being at least to
some extent controlled by the food packaging.
The history of the fundamental thermodynamic reasoning in developing models
of temperature effect on reactions, going back to the late nineteenth century with Van't Hoff
(1884), Hood (1885) and Arrhenius (1889), has been reviewed by Bunher (1974). The
most prevalent and widely used model is the Arrhenius relation, derived from
thermodynamic laws as well as statistical mechanics principles where:
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