Use of Scanning Electron Microscopy to Investigate the Effect of Drying Method on the Essential Oil Content of Two Thyme Genuses

The effects of drying method and prediction of the essential oil contents of two thyme genuses (Thymus Vulgaris and Zataria multiflora) were investigated using Scanning Electron Microscopy (SEM). T. vulgaris was dried at 30°C under controlled conditions while Z. multiflora dried through traditional method and at 50-70°C. In the middle and edge of Z. multiflora leaves, 18.4 and 14.9% of glands were destroyed, respectively, while all the glands in T. vulgaris leaves being kept intact. SEM results confirmed that the controlled drying method was more than the traditional drying (uncontrolled and at high temperatures) method. Extraction results from both Clevenger and microwave-assisted hydrodistillation methods indicate that the extraction yield from Z. multiflora (3.44 and 3.66 percent, respectively) was at least 44% more than that from T. vulgaris (2.39 and 2.52 percent, respectively). Extraction yield results are in good agreement with the SEM images of two thyme genuses. The number of glands per surface area in Z. multiflora leaf was more than that in T. vulgaris leaf.