An approach for isolation of oregano essential oil using ultrasounds

Given the demand for oregano oil in the food, pharmaceutical, and cosmetic industries, in this work for the first time an attempt was made to investigate innovative methods for extracting essential oil from oregano in order to reduce energy consumption and ensure high-quality product. Three different methods of distillation, conventional hydrodistillation (CH) and hydrodistillation with ultrasound application (UH) and with ultrasound pretreatment (UPH) were examined using a frequency of 20 kHz and an intensity ranging from 65 to 120 W. For each method, various parameters (amplitude level, pulse duration/pulse interval ratio, and treatment time) were examined for their effect on oil yield. The optimum distillation method and operating conditions were determined. The obtained oils were analyzed by gas chromatography–mass spectrometry (GC–MS) and characterized for their total phenolic content and antioxidant activity. In all treatments, the oil was collected at various time intervals and two mathematical approaches were selected for the kinetic modelling, namely, the first order kinetic model and the Peleg’s model. Ultrasounds led to an increase in oil yield of 8% for UPH and 17% for UH, as compared to the conventional method, shorter distillation time, and slightly higher energy consumption that can be ignored taking into account the high price of the oil. The composition of oils distilled by ultrasounds was not differed from that of oil produced with the classic method. The use of ultrasounds increased the total phenolic content of the oils, whereas their antioxidant activity did not differ from that of the conventional product.