Feasibility of extraction of oil from dehulled rapeseed cake using supercritical CO2

Abstract: The double-low rapeseed contains ≤2% erucic acid in its oil and ≤35μmol/g of dry meal. The oil of double-low rapeseed contains very low levels of saturated fatty acids (6%), high levels of oleic acid (≥60%), and intermediate levels of linoleic and linolenic acids (20 %and 10 %, respectively). Because of its higher oil content and numerous agricultural advantages, double-low rapeseed is getting worldwide attention. The rapeseed oil, which was extracted by a traditional process with pre-press and solvent extraction, is of bad quality. Commercial hexane, which has been used as a solvent for crude edible oil extraction, has toxicological and environmental safety issues. Carbon dioxide in its supercritical state has properties and extraction capacities very similar to liquids. Supercritical carbon dioxide extraction is a new technique for oil extraction and is similar to conventional solvent extraction in that the material to be extracted is withdrawn from the substrate by using a solvent. In its supercritical state, carbon dioxide is the most commonly used supercritical solvent due to its nontoxicity, non-flammability, low cost, availability in bulk quantities, ease of removal from the extracted materials, and low critical temperature and pressure (31.06 ℃ and 7.38 MPa, respectively). To improve the additional value of oils and meals obtained from the cold press cake of double-low dehulled rapeseed, supercritical CO2 is used to extract double-low rapeseed oil and then the quality of the oil and meal obtained is studied. The affection of factors, which includes extraction pressure, temperature, and time effecting on oil yield, is investigated by Box-Behnken's response surface methodology. The model equation for predicting the optimum response values is established by Design Expert software. The adequacy of the model equation for predicting the optimum response values was effectively verified by the validation. The experiment result indicates that affection of extraction pressure and time on oil yield are more significant than extraction temperature. The interaction between extraction pressure and time has a very significant affection on oil yield. The optimum operation parameters of supercritical CO2 extraction are: extraction temperature 40℃， pressure 28MPa, and time 120min．In this optimal condition, the oil yield is 95.08% and is similar to the 95.30% predicted as maximum oil yield by the mathematical model under the condition of temperature 39.66℃ and pressure 27.50MPa with extraction time 120 min. The supercritical CO2 extraction of double-low rapeseed oil from dehulled cold press cake has a lighter color and better acid and peroxide value compared to n-hexane extraction. The phospholipid content of oil extracted with supercritical CO2 is 0.051mg/g, which is 1/32 of the n-hexane process, and the vitamin E and total phenolic content are 17.68ug/g and 5.17ug/mL respectively, which are both larger than the n-hexane extraction process. The meal of double-low rapeseed obtained from dehulled cold press cake with supercritical CO2 extraction, which has a superior quality compared to the meal obtained by n-hexane extraction, has lower glucosinolate content, high protein solubility, and better color. These study results can help utilize cold press cake of dehulled double-low rapeseed for high-value purposes.