Investigation of Different Drying Methods of Peppermint (Mentha piperita) Medical Plant

Agriculture products, especially medical plants after harvest should be processed by different processes such as removal of foreign bodies, washing and cleaning, drying, packaging and so forth. One of main postharvest stages of medical plant especially peppermint is drying process.
The aim of this study is design a solar dryer equipped with double pass collector to drying process of peppermint and comparison their results with traditional drying methods (sun and shade).
In this study drying process of peppermint with different methods of solar drying (by solar dryer designed in this study) and also traditional drying (shade and sun drying) were investigated and compared.
The drying time required for dehydration of peppermint in solar drying method was 150 min, which it was approximately 82% and 55% shorter than to traditional methods of shade and sun. Furthermore, dehydration rate in drying methods of solar drying, sun drying and shade drying were 26.77, 12.48 and 4.48 (kg H2O/kg D.M h), respectively. The results of mathematical modelling indicated that Midli and kucuk (in drying methods of solar and shade) and Aghbashlo et al (in drying method of sun) can be fitted drying curve of this medical plant with high accuracy. Also, solar drying by dryer could be protecting the essential oil of this plant in the best form. The results show that the main components of peppermint essential oil was included: 1,8-Cineole, cis-Sabinene hydrate, Menthone, Menthofuran, iso-Menthone, Menthol and iso-Menthol
Generally, solar drying method of peppermint was recommended as the best method for postharvest processing of this medical plant.