Woldeyes, Belay (PhD)Belay, Zelalem2018-07-172023-11-102018-07-172023-11-102017-06http://etd.aau.edu.et/handle/12345678/8957Essential oils are very interesting natural plant products, and among other qualities they possess various biological properties. This study has been carried out to extract the essential oil from the leaves of Ocimum Lamiifolium using steam distillation. Ocimum Lamiifolium is an indigenous plant in Ethiopia and is locally called “Dama-Kesse’’ (in Amharic). It is among the commonly occurring Ocimum species that distributed in different regions of Ethiopia. The average optimum yield of the essential oil in percentage from 100 g of plant materials is 0.4133 ± 0.0208% (v/w) and extracted at a temperature of 85ºC, 4 h extraction time and <1mm particle size of plant materials. The essential oil was analysed by combined Gas Chromatography and Mass Spectroscopy unit, and it was found to been riched in Sesquiterpenes (93.69%) and oxygen containing components. Among the major components from the GC-MS analysis which accounted 69.83% were β-Bisabolene (29.52%), caryophyllene (14.57%), Elemicin (14.29%) and Germacrene D (11.45%). The main and interaction effects of the process parameters (temperature, extraction time and particle size) and the optimum conditions were examined using design expert 7.0.0 software. In the investigation all the main factors had a significant effect, but no significant interaction effects of the parameters had shown on the yield of the essential oil. The model adequacy also investigated by normal probability plot of residuals and plot of residual verses predicted value. Both plots have shown that the model was acceptable. Finally, the optimum conditions of the process parameters for the extraction were optimized and the optimal treatments of each factor to maximize the yield were 87.24°C of temperature, 4.85 hours (4 hours and 51 minutes) of extraction time and <1 mm of particle size. The maximum yield that was obtained at these optimum conditions using 100 g of dried leaves of the plant materials was 0.418748 ± 0.0208% (v/w). Key words: Composition, essential oil, extraction, GC-MS, Ocimum Lamiifolium, steam distillation,yield.enComposition;essential oil; extraction; GC-MS; Ocimum Lamiifolium; steam distillation;yieldThesis