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

and variable temperature conditions, with the expressed (or implied) assumption that the
other factors are constant. Controlled temperature functions like square, sine, and linear
(spike) wave temperature fluctuations can be applied to verify the Arrhenius model,
developed from several constant-temperature shelf life experiments . Labuza (1984) gives
analytical expressions for Eq. (44) for the above temperature functions using the Q 10
approach. Similarly solutions can be given using the Arrhenius or square root models.
To systematically approach the effect of variable temperature conditions the
concept of effective temperature, T eff , can be introduced. T eff is a constant temperature that
results in the same quality change as the variable temperature distribution over the same
period of time. T eff is characteristic of the temperature distribution and the kinetic
temperature dependence of the system. The rate constant at T eff is analogously termed
effective rate constant, and Q i (A i ) of Eq.(44) is equall to k eff t. If T m and k m are the mean
of the temperature distribution and the corresponding rate constant respectively, the ratio Γ
is also characteristic of the temperature distribution and the specific system, where
Γ= k eff
k m
(48)
For some known characteristic temperature functions shown in Fig.8 analytical
expressions for the Q 10 and Arrhenius models are tabulated in Table 5.
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