High intensity ultrasound assisted extraction of oil from soybeans

The application of 20 kHz high-intensity ultrasound during extraction of oil from two varieties of soybeans (TN 96-58 and N 98-4573) using hexane, isopropanol and a 3:2 hexane–isopropanol mixture was evaluated. In a simplified extraction procedure, ground soybeans were added to solvents and ultrasonicated between 0 and 3 h at ultrasonic intensity levels ranging from 16.4 to 47.6 W/cm2. Oil was recovered after distillation and yield and composition determined. Using hexane as a solvent, yield generally increased as both application time and intensity of ultrasound increased. Solvent type influenced the efficiency of the extraction, i.e., the highest yield was obtained using ultrasound in combination with the mixed solvent. Gas chromatography analysis of ultrasonicated soybean oil did not show significant changes in fatty acid composition. Results were attributed to mechanical effects due to ultrasonically induced cavitation increasing permeability of plant tissues. A comparison of scanning electron microscopy images of raw and ultrasonicated soybeans indicated development of microfractures and disruption of cell walls in ground soybean flakes. Our study suggests that high-intensity ultrasound may reduce time required to extract edible oils from plant sources and hence improve throughput in commercial oil production processes.