Drying of olive (Olea europaea L.) leaves on a conveyor belt for supercritical extraction of bioactive compounds: Mathematical modeling of drying/extraction operations and analysis of extracts

The influence of drying conditions on the composition of supercritical extracts recovered from olive leaves was investigated. Leaves were dried on a conveyor belt and the effects of air temperature and residence time on the extraction kinetics, global yield, antioxidant activity, total polyphenols content and chemical profiles of the extracts were evaluated. Inlet air temperatures of 50, 60 and 70 degrees C with residence times of 180, 120 and 60 min, respectively were tested. A model based on mass and energy balances with effective heat and mass transfer coefficients fitted from experimental data was used to describe the drying process. The temperature and output moisture of the leaves were well predicted by the model. The extraction kinetics was not significantly affected by the drying conditions (air temperature and residence time), but the extraction yield was enhanced for samples dried at 50 degrees C/180 min whereas the higher values of antioxidant activity and phenolic contents were found at 60 degrees C/120 min. Sovova's model was effective in describing the supercritical extraction of olive leaves and can be used to estimate the extraction kinetics and mass transfer coefficients.