Evaluation of six drying treatments with respect to essential oil yield, composition and color characteristics of Thymys daenensis subsp. daenensis. Celak leaves.

摘要

Thymus daenensis subsp. daenensis. Celak is known as an endemic and valuable spice plant. The effect of six different drying treatments (sun, shade, oven 50 degrees C, oven 70 degrees C, microwave and freeze-drying) on the essential oil yield, composition and color characteristics of leaves was assessed. The essential oils from fresh and dried samples were isolated by hydrodistillation in a Clevenger apparatus and analyzed using gas chromatography-mass spectrometry (GC-MS). The highest essential oil yields were obtained by freeze-drying (1.7%) followed by oven 50 degrees C (1.46%), sun drying (1.42%), oven 70 degrees C (1.01%), shade drying (0.91%) and microwave (0.89%). Results showed that air drying at ambient temperature increased significantly the essential oil yield. Higher temperatures (microwave and oven 70 degrees C) lead to increase in thymol/carvacrol and beta -caryophyllene content. In this study, Lightness (L*), greenness (a*), and yellowness (b*) of dried leaves were also compared with fresh one. Oven drying at higher temperature resulted in a considerable decrease in the color quality of the leaves. Air drying and oven 50 degrees C and 70 degrees C had the highest yellowness in comparison to other treatments. In spite of relatively low essential oil yield in Microwave drying, this method had many advantages such as shortening of drying time, high color quality and increased major compounds of thyme leaves.CAS Registry Numbers 89-83-8