Effect of different drying methods on the essential oils of mint (Mentha haplocalyx)

The essential oils of fresh, shade-dried, sun-dried, and oven-dried mint of Mentha haplocalyx Brig., and the shade-dried herbs after one hour of soaking were analyzed by GC-MS to provide a scientific basis to regulate the drying methods. Fifty-nine compounds were isolated and identified, including 35 from fresh herbs, 25 from shade-dried herbs, 23 from sun-dried herbs, 17 from oven-dried herbs and 48 from shade-dried mint after one hour of soaking. Eighteen compounds were common to all five samples, including menthol, menthone, and isomenthone, which were the main components. Several of these significantly decreased in shade-dried mint soaked in water. Thus in cleaning and drying processes soaking mint in water should be avoided as far as possible, in case major components are extracted thus producing an inferior product that will undermine its curative effect.