Effect of ultrasonic field on extracting oil from sunflower seed using sub-critical carbon dioxide was studied. Experimental results indicated that the extraction yields of sunflower seed oil using sub-critical carbon dioxide could be obviously enhanced by ultrasonic field. After extracting 240 minutes, extraction yields with ultrasound(100 W/L, 4 s/6 s) and without ultrasound were 94.81% and 74.82% under 25 MPa, 30 ℃ and 3 L/h, respectively. Density of ultrasonic power and ultrasonic frequency fairly greatly affected the extraction yield, with increasing of density of ultrasonic power, extraction yield enhanced. Compared with 38 kHz ultrasound, 20 kHz ultrasound had advantage of extraction. It was reasonable to adapt 4 s/6 s model of ultrasonic wave irradiation, at the same time, initiation time of ultrasonication had some effects on the extraction yield. Results of GC/MS analysis showed that ultrasonication had not changed ingredients of sunflower seed oil and structure of every component. The mechanism of ultrasound enhancement in sub critical carbon dioxide might be attributed to mechanical fluctuant and thermal effects.
