Effect of ultrasound transducer design on the acoustically-assisted supercritical fluid extraction of antioxidants from oregano

Power ultrasound is applied in food technology to intensify extraction processes, due to the phenomena ultrasonic energy induces in the medium, enhancing mass transfer. The purpose of this work was the acoustic characterization of four transducers of different geometries and the evaluation of their performance in the ultrasonically assisted supercritical fluid extraction of antioxidants from oregano. The transducers differed in the amount of energy transmitted into the medium. Designs varied from the base model (T1), a larger cylindrical headmass (T2), a stepped circular section sonotrode (T3) and a multiplate configuration (T4). The highest nominal power density provided according to the calorimetric method was for T4 (151.6 ± 7.1 W/L). The T2 produced a more uniform acoustic field and a higher acoustic pressure (150.6 ± 20.5 kPa). Both parameters had an impact on total phenolics and antioxidants extraction with CO2 under supercritical conditions (35 MPa, 35 °C, 2.3% ethanol as co-solvent). T4 and T2 were equally efficient (4.0 ± 0.2 and 4.2 ± 0.2 mg GA/g) for phenolic extraction, and with respect to antioxidant capacity, the best performance was that of T4 (26.4 ± 1.1 μmol TE/g). Of the antioxidant compounds extracted, flavones and flavanones were identified. Therefore, transducer geometry influenced the amount and distribution of energy transmitted into the medium, thus determining the efficiency of the extraction process.