Frozen mirabelle plum drying: Kinetics, modelling and impact on biochemical properties

The aim of this research was to study and model the kinetics of the hot air drying of frozen mirabelle plums. Effects of temperature (50-85 °C), air velocity (0.6-1.2 m/s) and a pre-treatment (ascorbic acid + sucrose-saturated solution) were investigated. The sorption isotherm and heat of sorption of mirabelle plum were mathematically described respectively by the Guggenheim, Anderson and de Boer (GAB) model and a new one. Depending on temperature and air velocities, the effective diffusivity and the energy of activation were respectively in the range of 8-16.8 × 10⁻¹⁰ m² s⁻¹ and 43.7-55.14 kJ mol⁻¹. To establish the model best adapted to describe this process the fit quality of five models (Newton, page, modified page, logarithmic and diffusion) were evaluated and compared. The diffusion model led to low values of reduced χ-square, mean square root and mean relative deviation modulus with the highest linear regression coefficient. This model was validated in a large range of operating conditions and represents an excellent tool to predict the duration of this process. The pre-treatment preserves biochemical properties of the dried mirabelle plums (reducing sugar content, total phenolic compounds and anti-oxidant activity).