Optimizations and comparison of two supercritical extractions of adlay oil

Oil is an important component of adlay seed (Coix lachrymal-jobi L. var. Adlay) with many beneficial functions to human health. In this work, a supercritical fluid extraction (SFE) and a novel ultrasonic-assisted supercritical fluid extraction (USFE) were studied and compared. Their operating conditions on the oil extraction, including extraction temperature (T), pressure (P), time (t), and CO2 flow rate (F), were optimized. Based on the yield of extraction, the favorable conditions for SFE were: T at 45 °C, P at 25 MPa, t at 4.0 h and F at 3.5 L/h. While ultrasound was applied as in USFE, the following parameters were preferred: T at 40 °C, P at 20 MPa, t at 3.5 h and F at 3.0 L/h, respectively. The results show that supercritical fluid extraction with the assistance of ultrasound could reduce the temperature, pressure, CO2 flow rate, as well as time used in the process. Compared with SFE, USFE could give a 14.0% increase in the yield for extracting oil from adlay seed with less severe operating conditions. According to the quality of adlay oil and the analysis of its fatty acids by GC-MS, there was no significant difference between USFE and SFE.Industrial relevanceAdlay oil is an important component of adlay seed (Coix lachrymal-jobi L. var. Adlay) with many beneficial functions to human health. In China, there is already this kind of product produced by factories. However, its production method is conventional solvent extraction. Although supercritical fluid extraction has obvious advantages compared to conventional extraction method, it has also some disadvantages such as low extraction efficiency for some components, very high operation pressure and safety problem. In our work, a novel ultrasonic-assisted supercritical fluid extraction (USFE) was studied and compared. As an emerging technology, it has huge potential and remarkable significance in its application in adlay oil and other relevant products' production at factory-scale. The experimental results and conclusion will provide a useful background to application of the novel technology in industrials.

► We optimize and compare two supercritical extractions of adlay oil with and without ultrasound.
► The optimal operating conditions on the two extractions of adlay oil were gotten.
► Ultrasound gave a 14.0% increase in the yield of adlay oil with less severe operating conditions.
► There was no significant difference between the qualities and fatty acids of the oil extracted by two methods.