Thin-layer convective air drying of lemon verbena (lippia citriodora) leaves

Lemon verbena leave is a flavoring food additive as well as a good source of valuable compounds such as essential oils, flavonoids and phenolic acids. However, similar to many other aromatic plants, lemon verbena leave is perishable due to its high moisture content. The aim of this work was to study the effect of air temperature (45, 55, and 65°C) on the quality attributes of lemon verbena leaves during hot-air drying (HAD). The drying kinetics were also modeled. The results showed that higher drying temperature led to a significant decrease (p˂0.05) in the rehydration ratio due to a change in the structural features of the dried leaves. The essential oil content of dried samples was also significantly different (p˂0.05) from that of the fresh leaves due to high loss of volatile components and ranged from 0.42 to 0.85. Moreover, a significant increase in the value of effective moisture diffusivity (Deff) and color change was observed when the samples were dried at 65°C compared to 45°C. The value of Deff varied from 1.140×10-10 to 2.280×10-9 m2/s and the activation energy was found to be 31.04 kJ/mol. The greatest R2 (≥0.999) and the lowest RMSE and SSE were obtained for the Naghavi et al. model (proposed in this research)