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

properly handled and would indicate remaining shelf life. Use of TTI as "consumer
indicators" is the ultimate goal of these systems.
A variety of TTI based on different physicochemical principles have been
described by Byrne (1976) and Taoukis et al.(1991). Statistical correlations of TTI
performance and product quality characteristics have been reported for a variety of
perishable and frozen foods (Tnker et al.,1985; Chen and Zall,1987; Wells and
Singh,1988). A general approach that allows the correlation of the response of a TTI to the
quality changes of a food product of known deterioration modes, without actual
simultaneous testing of the indicator and the food, was developed by Taoukis and Labuza
(1989a). Three types of TTI commercially available were mathematically modeled using
Arrhenius kinetics. One type is based on a time-temperature depended diffusion of a dye
along a wick , the second on a change of color due to a controlled enzymatic reaction and
the third on development of color based on a solid state polymerization . A scheme was
introduced that allows the correlation of the TTI response, X, to the quality index A of the
food. X can be expressed as a function of time:
F(X) t = k t = k I exp(-E A / RT) t (52)
where F(X) is the response function of the TTI, t is the time and k the response rate
constant; the constant k I and the activation energy E A are the Arrhenius parameters.
For a
TTI going through the same temperature distribution, T(t) as the monitored food, the value
of F(X)t is known from the response X ; Teff can then be calculated from equation (14)
for T=T eff . T eff and knowledge of the kinetic parameters of deterioration of the food
allows the evaluation of Q(A) and hence the quality loss of the product. The reliability of
the TTI under variable temperature conditions was also assessed(Taoukis and Labuza,
1989b), using the relations of Table 5, and in general was judged satisfactory.
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