CONVECTIVE SOLAR DRYING OF OLIVE LEAVES

This paper presents investigations on thin layer convective solar drying of four olive leaves varieties (Chemlali, Chemchali, Chetoui and Zarrazi). Olive leaves were dried at three drying air temperatures (40, 50 and 60C) and at two drying air velocities (0.566 and 1.133 m/s). The drying air temperature is the main factor in controlling the drying rate. The experimental drying curves show the presence of only a falling rate period. Mathematical models, namely, Newton, Page, Henderson and Pabis, Logarithmic, Wang and Singh, Two-term and Two-term exponential models were fitted to the experimental data. Among these models, the Logarithmic model showed the best agreement with the experimental data. The effective moisture diffusivity was estimated by applying the Fickian law to the drying kinetics. The effective moisture diffusivity values varied from 3.437 10−10(Chemlali variety) to 2.427 10−9 m2/s (Chemchali variety). The values of activation energy were calculated assuming an Arrhenius-type temperature reliance. The activation energy ranged from 24.704 (Chetoui variety) to 53.743 (Chemlali variety) kJ/mol. The quality attributes of the dehydrated olive leaves samples were investigated in term of color. The effect of solar drying on L*, a*and b*parameters was significant (P < 0.05) for all the studied olive leaves. PRACTICAL APPLICATIONS This work concerns the investigation of the drying characteristics of olive leaves. Like many other medicinal plants, olive leaves should be dehydrated before use to preserve their active compounds which have numerous applications in the pharmaceutical, cosmetic and food preservation industries. Therefore, the study of the drying characteristics is essential for the industrial and the academic purposes.