Comparison of Essential Oil from Ocimum Basilicum Obtained via Sequential Ultrasound-Microwave Extraction with Microwave Method

Determining the best extraction method to obtain high yield of essential oils from medicinal plants has been identified as one of the challenges in scientific research. The sequential ultrasound-microwave method is a new extraction method that in this research has been applied to extraction of essential oil from basil. In order to investigate the effect of this approach on enhancing extraction yield, the microwave method was examined as a base method. To optimize the extraction conditions of the sequential method, ultrasonic power, microwave power, and extraction time were determined as independent variables and essential oil yield as response. Experiments were modeled by central composite design (CCD) of response surface methodology (RSM). The highest yield (2.3% w/w) was obtained at 300 W of ultrasonic power, 600 W of microwave power, and 40 min of extraction time. While the base method yield was 0.74% w/w. The chemical composition analysis of the active compounds showed that the number of compounds in the sequential approach is higher than those in the microwave method. Furthermore, by comparing the antioxidant properties obtained by DPPH and FRAP methods, the sequential method was better in preserving the antioxidant properties of basil essential oil. Scanning electron microscopy images also showed more damage to the glands containing the active ingredients by the sequential process than the base method. Generally, the sequential ultrasound-microwave method can be introduced as an efficient method for the extraction of essential oils from Ocimum basilicum.