Effects of Microwave Drying on the Yield and Chemical Composition of Essential Oils of Artemisia afra Jacq. Ex willd from the Eastern Free State South Africa

The effects of various drying methods on yield and content of the essential oil of Artemisia afra were studied. The results showed that the yield was higher in fresh than in dried leaves. The recorded yields were 1.04 %, 0.92 %, 0.94 %, 0.13 % and 0.74 % for fresh, air, sun, microwave and oven dried leaves respectively. A total of 65 compounds were identified, 20, 16, 14, 36, and 15 compounds were from fresh, air dried, sun dried, microwave dried and oven dried plant materials respectively. Monoterpernoids, beta-thujone (60.45, 60.63, 54.57 and 49.43 %) alpha-thujone (18.11, 16.90, 15.10 and 12.54 %), 1,8-cineole (8.91, 7.68, 7.20 and 7.36 %) and chrysanthenyl acetate (6.85, 10.30, 10.04 and 9.37 %) were prominent components in the fresh, air, sun and oven dried material. While sesquiterpenes trans-caryophellene (36.91 %), ledene (10.28 %), germacrene D (5.43 %) were the prominent compounds in the microwave dried material and alpha-thujone (15.27 %) as the only prominent monoterpernoid. The microwave drying was the only method that brought about significant change in the major components of the oil by the complete removal of 1,8-Cineole and the popularly known toxic beta-thujone. The expulsion beta-thujone through microwave drying could bring about the recommendation of A. afra oil for human consumption in order to achieve the expected medicinal purposes. To the best of the author's knowledge, this is the first report on the effect of microwave drying on the chemical composition of A. afra essential oils.