Modeling Kinetics of Rosemary Drying (Rosmarinus officinalis L.) Using Infrared

Rosemary is an evergreen and aromatic plant of the mint family, which has many antioxidant and medicinal properties. Nowadays, to increase the quantity of extraction and improve the quality of essence, the plant is dried and then the extraction process is performed. Thus, new and combined methods for drying of plants containing essence have been studied. Different drying methods such as hot air, microwave, microwave- vacuum, sun and freeze drying have been studied by many researcher to dry rosemary and the quality of the extracted essence and the kinetics of mass transfer have been investigated. Drying by means of infrared is considered for many agricultural products but this method has not been applied to rosemary until now. Therefore, the purpose of this study was to investigate the kinetics of drying and the effect of infrared drying on the volume, color and quality of essence of rosemary leaves. Our specific target was modeling of the infrared drying process and compare it with other drying methods.

In this study, the geometric properties of rosemary leaves were measured by Mitutoyo Micrometer. Then, by using electromagnetic radiation in the range of infrared spectrum (100, 200 and 300watts) freshly prepared leaves of rosemary were dried. After essence extraction by clevenger method, the volume of extraction and components were determined by GC/MS and according to the power of infrared wavelength were evaluated by completely randomized design. The quality of dried rosemary and essences were also studied by ImageJ software, and color parameters a*, b*, L*, chroma (C*), browning index, total color difference and Hue angle, were calculated by completely randomized design. In addition, drying curves, effective diffusivities and activation energy determined by using moisture measurement data.

According to the results of analysis of variance and Duncan's Multiple Range test at 5% level, it was observed that with increasing the power of the infrared lamp in the drying process, color parameters like L, b, Chroma and BI in dried rosemary decreased and ΔE, A and Hue angel increased. Analysis of variance and comparison of Duncan's mean at 5% level showed that increasing the infrared power has a significant effect on reducing the volume of essence. In the case of essence color, it was perceived that with increasing the power of the infrared lamp, the color parameters like A, L and Hue angel decreased and b, BI and Chroma increased. Furthermore, increasing the infrared power in the drying process of rosemary has a significant effect on reducing the volatile compounds of rosemary essence. Effective diffusivities varied from 33.3×9.10-9 to 1.0907×10-8. The activation energy was also determined as 30.243 kW/kg. To predict the rosemary drying trend by using eight models, regression modeling was performed through MATLAB software (version 2016). Results showed that, Midilli model for the power of 200 and 300 watts and Verma model for the power of 100 watts, due to high correlation coefficient index and low standard error, were two suitable models for evaluation of Drying kinetic and prediction of drying process.

Increasing infrared power during drying process of rosemary leaves decreases the efficiency of essence extraction. Moreover, increasing the infrared power has a significant effect on reducing the active ingredients like cineol and Beta-Pinene in essence. The color of dried rosemary and extracted essence are affected by infrared radiation power and varies with increasing the power. Rising the infrared radiation power results in an increase in the effective diffusivity coefficients. Also, it can be concluded that, midilli and verma are two best models for prediction of drying trend of rosemary.