THE EFFECT of INTERNAL THERMAL GRADIENTS ON the RELIABILITY of SURFACE MOUNTED FULL-HISTORY TIME-TEMPERATURE INDICATORS

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Abstract
A simple analytical expression aimed at assessing the theoretical reliability of a full-history time-temperature indicator placed on the surface of a food item as a predictor of the remaining shelf-life in the presence of heat transfer limitations within the food is obtained. Such expression, which depends on three dimensionless parameters only, can be written as a univariate function of a single parameter containing the thermal properties of the food via a suitable algebraic scaling. the derivation of the relevant formulae is based on the integration of a generic quality function across the slab-shaped food item under the assumption that the temperature on the surface of the food undergoes a sinusoidal variation with time. the analysis reported is useful because it provides a quick estimate of the effect of the thermal diffusivity of the food on the relative error associated with the use of a TT1 when the activation energies of the food and the indicator are matched (as should happen in the idealistic case) under realistic environmental conditions of storage.