Drying of Mentha piperita leaves on a fixed bed at different temperatures and air velocities

ABSTRACT The species Mentha piperita, popularly known as peppermint, is not only a medicinal plant but is also used in the pharmaceutical, food and cosmetic industries. Consequently, the drying process is necessary to increase shelf and product life, facilitating transport, handling and storage. For mint derivatives of quality, work into pre- and post-harvest is necessary. The aim of this study was to evaluate drying. To obtain the curves, temperatures in the range of 30 ºC to 70 ºC were used, with drying air velocity varying between 0.3 and 0.5 m.s-1. For drying the leaves, a laboratory-scale, fixed bed dryer was used, having a fan to move the air and a heating system. The results showed that the Midili model best fit the experimental data. The relationship of the diffusion coefficient to the drying temperature can be described by the Arrhenius equation, giving an activation energy of 68.42 KJ mol-1for a velocity of 0.3 m.s-1, and 78.27 KJ mol-1 for a velocity of 0.5 m.s-1.

摘要 辣薄荷（Mentha piperita）俗称薄荷，既是药用植物，也广泛应用于制药、食品及化妆品工业。因此，干燥工艺是延长产品货架期与使用寿命、便于运输、装卸与存储的必要环节。为获得高品质的薄荷衍生产品，采收前后的相关研究工作必不可少。本研究旨在评估薄荷干燥过程。为获取干燥曲线，实验设置的干燥温度区间为30℃至70℃，干燥空气流速介于0.3~0.5 m·s⁻¹之间。本实验采用实验室规模的固定床干燥机对薄荷叶片进行干燥，该设备配有送风风机与加热系统。结果表明，Midili模型对实验数据的拟合效果最优。扩散系数与干燥温度的关系可通过阿伦尼乌斯（Arrhenius）方程描述：当空气流速为0.3 m·s⁻¹时，活化能为68.42 kJ·mol⁻¹；当流速为0.5 m·s⁻¹时，活化能为78.27 kJ·mol⁻¹。