Effects of microwave heating on the antioxidant and insecticidal activities of essential oil of Origanum glandulosum Desf. obtained by microwave steam distillation

Response surface methodology (RSM) was used for the first time to investigate the efficiency of a new process developed in our laboratory: Microwaves Steam Distillation (MSD) on the oregano essential oil extraction. The selected parameters are steam flow, microwave power and extraction time, the response is essential oil yield. According to the statistical method, a second-order polynomial function was assumed to approximate the yield. The coefficient of determination R2 (91.33%), revealed a quite agreement between experimental and predictive values. Optimal conditions were: 6 g. min(-1) for steam flow, 300 W for microwave power and 8 min for time. DPPH tests showed that MSD oil was the most efficient than eugenol, SD oil and the main compounds (carvacrol and thymol), and has comparable antioxidant activity to that of BHT. In the other hand, MSD and SD oils have an insecticidal effect against Rhizopertha dominica, but SD oil was most efficient.