Granola is a dried granulated breakfast cereal product susceptible to moisture uptake. Therefore, being a moisture sensitive product it is dependent on the environmental conditions of storage, which can lead to undesirable product changes. The kinetics of moisture adsorption is an important tool to model product quality deterioration considering varying storage conditions. The aim of this study was to investigate the moisture adsorption kinetics and loss of firmness of granola under different environmental conditions (temperature and relative humidity), and develop a mathematical model describing the kinetics of quality decay of granola as a function of temperature and relative humidity. Samples of granola were stored in airtight containers at different relative humidities (32-33, 53-57 and 75-76%) and temperatures (10, 20, 30 and 40°C). Moisture uptake and firmness loss showed an exponential growth and decay, respectively, which could be described by a first order reaction model. The effect of temperature and relative humidity on the reaction rate constant of firmness was not significant. The first order reaction model was shown to be a suitable model to describe the firmness loss as a function of time. The reaction rate for the moisture gain showed a temperature dependency, which was described by the Arrhenius equation. Therefore, an overall kinetic model was developed to described the quality decay in granola during storage as a function of temperature, and a good fit (R2 0.968) was found.
Keywords: quality decay, kinetic modelling, lumped capacity model, moisture content, water activity