As a novel technique, supercritical CO2 (SC-CO2) extraction enhanced by ultrasound was applied to the extraction of lutein esters from marigold and the extraction curves were described by Sovova model. The mass transfer coefficient in the solid phase (k(s)) increased from 3.1 x 10(-9) to 4.3 x 10(-9) m/s due to ultrasound. The effect of extraction parameters including particle size of matrix, temperature, pressure, flow rate of CO2, and ultrasonic conditions consisting of power, frequency and irradiation time/interval on the yield of lutein esters were investigated with single factor experiments. The results showed that the yield of lutein esters increased significantly with the presence of ultrasound (p < 0.05). The maximal yield of lutein esters (690 mg/100 g) was obtained for a particle size fraction of 0.245-0.350 mm, extraction pressure of 32.5 MPa, temperature of 55 degrees C and CO2 flow rate of 10 kg/h with ultrasonic power of 400 W, ultrasonic frequency of 25 kHz and ultrasonic irradiation time/interval of 6/9 s. (C) 2009 Elsevier B.V. All rights reserved.