Supercritical Carbon Dioxide Extraction of Vegetable Oils: Retrospective and Prospects

Supercritical carbon dioxide (SC-CO2) extraction is projected as one of the most viable alternatives to conventional hexane extraction due to its density-dependent solvent power, low viscosity, moderately high diffusion coefficient, and low-temperature operative conditions. Demands for retention of bioactive compounds in oils like wheat germ oil, rice bran oil, almond oil, etc., are increasing and that can be easily met up by this alternative solvent. Solvent extraction of oils rich in polyunsaturated fatty acid, like flaxseed oil, microbial oil, etc., is highly sensitive. Prolonged heating during removal of solvent often leads to degradation of essential fatty acids. As the phase change is done by changing the pressure, the use of SC-CO2 overcomes such issues. It is quite evident that degumming, one of the processing steps in refining of vegetable oils, will not be required if SC-CO2 is used for extraction. Moreover, in some other cases, bioactive compounds will be retained in the de-fatted meal and can be recovered with better purity. All these factors will add to the overall economy. A detailed review of the application of SC-CO2 for the extraction of vegetable oils-the initial reports, current status, and future prospectsis presented in this paper. Practical applications: In recent years, the oils and fats industry has gone through several technological advancements and the most important of them was shifting to physical refining process from highly polluting chemical process. The industry may see another major change in the extraction process in the near future. Hexane has been enlisted as a hazardous air pollutant as per the Clean Air Act, 1990. Recent reports show that hexane may have some role even in ozone layer depletion. Scientists are looking forward to alternatives. SC-CO2 has emerged as one of the most suitable alternatives. The large capital investment required for the installation of SC-CO2-based extraction plants was a major drawback. However, ready availability of critical machineries and advancements in terms of automation has brought down the capital expenditure significantly. The utilization of superior quality by-products generated by the process of SC-CO2 extraction may be an added advantage for the overall economy of the process.