Factors influencing the drying of prunes 1. Effects of temperature upon the kinetics of moisture loss during drying

The kinetics of the drying of prunes (Prunus domestica) have been investigated as a function of temperature (70–100 °C). The variety of plum used was DʹAgen. The prunes were dried in an oven under exhaust conditions resulting in a constant relative humidity during drying (70–80%). It was found that simple first-order kinetics fitted the experimental data well. This is consistent with a diffusion-controlled process through the fruit matrix. The activation energy plot was found to be non-linear with a much higher activation (80 kj mol−1) at the lower temperature end. This indicates a more hindered path for diffusion of the water through the matrix. This is consistent with what is known about the temperature dependence of cell rupture and disturbance of structure in such a material. In addition, estimates of diffusion of water through the food matrix are much slower than the self-diffusion coefficient of water across the entire temperature range. This also emphasises the hindered nature of the process.