THIN-LAYER DRYING BEHAVIORS OF OLIVE LEAVES (OLEA EUROPAEA L.)

Recently, interest in olive leaves has increased because of their high phenolic contents. Although the critical process in olive leaf treatment is drying, the drying behavior of olive leaves has not been known yet in the literature. In this study, olive leaves were dried in a tray drier at the temperature range of 50-70C and velocity range of 0.5-1.5 m/s. Eleven different semitheoretical thin-layer drying curve models were used to characterize the drying behavior of olive leaves. Effects of drying air temperature and velocity on model coefficients were determined by multiple regression analysis. The correlation coefficient (r), the reduced chi square (chi 2) and the root mean square error (RMSE) were taken as the statistical criteria parameters for model comparisons. It was found that the modified Henderson and Pabis model represented drying characteristics best with r = 0.9955. Effective diffusivity was computed by taking account of temperature and air velocity. The temperature- and velocity-temperature-dependent activation energies were 60.97 +/- 3.21 and 75.98 kJ/mol, respectively. It was concluded that olive leaves could be dried successfully by thin-layer drying procedure, and the drying rate was influenced mainly by drying air temperature. PRACTICAL APPLICATIONS Olive trees are important plants covering similar to 8 million hectares in the whole world. Recent studies have shown that olive leaves have higher amounts of phenolic contents such as oleuropein and hydroxytyrosol. Oleuropein is especially a very valuable component in food, medicines and in the drug industry. Although the importance of olive leaves has been discussed in several scientific studies, there have been few studies for using olive leaves industrially. Because the main process in olive leaf treatment is drying, modeling and determining the drying behavior is an important step for designing and optimizing the olive leaf treatment. Unfortunately, there has been no study ever carried out explaining the drying behavior of olive leaves in open literature to the best of the authors' knowledge.