Modeling the quality decay kinetic of encapsulated ground coffee

A fully predictive model for quality decay kinetic of ground coffee packaged in bioplastics is not available today. Therefore, a new model is proposed to predict the kinetics of quality decay of encapsulated ground coffee (indicated as EGC), stored under constant temperature and relative humidity conditions. The proposed model assumed that a first-order type equation, with a kinetic constant dependent on water activity, can be used to describe the quality decay of EGC. To predict the variation of water activity inside the capsule over time, the mass balance of the water inside the capsule was carried out. Specific tests were conducted at 23 °C to estimate the model's parameters. Tests on ground coffee were run to estimate the parameters used to relate the kinetic constant to the water activity; the capsule filled with silica gel was used to determine the dependence of water permeability coefficient on the water activity inside and outside the capsule. The ground coffee water sorption isotherm at 23 °C was also determined. The quality decay kinetic of EGC was measured by monitoring the pH as reliable quality descriptor and it was used to assess the goodness of the model prediction. Results indicated that notwithstanding the numerous assumptions made to derive the new model, its ability to predict the quality decay kinetic of EGC is quite acceptable.