Modeling Degradation Kinetics in Dry Foods Storage under Varying Temperature and Moisture Content—Theoretical Evaluation

Abstract

The combined effect of temperature and moisture (or water activity) on the rate of nutrients loss and other deteriorative chemical reactions in foods has been primarily studied in relation to drying. In long foods storage, changes in their temperature and/or moisture content are much slower and never as dramatic, but their effect can be similar in kind. Reported degradation reactions in foods mostly followed first- or other fixed-order kinetics. Hence, their progress under dynamic conditions primarily depends on the varying rate constant. Perhaps the most economic way to describe the rate constant’s variations pattern and magnitude is a two-parameter temperature-dependence model whose two coefficients are moisture dependent, each described by another two-parameter model, which brings the total number of adjustable parameters to four. Such a flexible model is the two-parameter exponential temperature-dependence term, a simpler substitute to the Arrhenius equation, whose two parameters’ moisture dependencies are also described by two similar exponential terms. This model’s flexibility is demonstrated with computer simulations of chemical degradation under varying temperature and moisture conditions. Testing a large number of products stored for long times by the traditional methods to determine a reaction’s kinetic parameters and their temperature and moisture dependencies can create logistic problems. Theoretically, they can be avoided by estimating the kinetic parameters directly from several successive concentration determinations during a single dynamic storage experiment whereby the monitored temperature and moisture are allowed to vary arbitrarily. The principle is demonstrated with simulated data having no or very small errors. However, its practical implementation might not be effective if the experimental concentration measurements have a substantial scatter.