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Oil/Oilseed Chemistry
A two-step process for wheat germ oil extraction
T
he main objective of this study was to optimize the mechanical extraction process parameters to increase wheat germ oil yield without compromising oil quality. A two-step process, including pre-pressing wheat germ using a screw press followed by extracting residual oil from the pressed cake by aqueous and aqueous enzymatic extraction techniques also was examined.
Approach
A heavy-duty screw press was used to extract wheat germ oil from food grade, full-fat wheat germ. The screw press shaft speed, cage temperature, back pressure at the meal discharge end, shaft arrangement and germ pretreatment conditions were optimized for maximum oil yield. The highest oil yield, 47.7 percent, was obtained under the following conditions: severe shaft arrangement, cage temperature of 225 degrees Fahrenheit, germ pretreatment/heating at 180 degrees Fahrenheit, high back pressure and shaft speed at 400 rpm. The quality of oil obtained by mechanical pressing was better (low free-fatty acid, peroxide value and p-anisidine value and higher vitamin E content) than that for commercially hexane extracted crude oil. Considering that more than 50 percent of the wheat germ oil remained in the press cake after mechanical pressing, the efficacy of the aqueous oil extraction for residual oil recovery was examined. The extraction of press cake with a boric acid-NaOH (pH 8) buffer using fine ground material at liquid-to-solid ratio of 20:1 and extraction time of a half-hour resulted in about 80 percent oil recovery. Aqueous extraction of wheat germ allows simultaneous recovery of proteins and oil. Hence, the recommended process would be mechanical pressing of full-fat wheat germ followed by aqueous extraction of the cake obtained from a mechanical press. This two-step process would recover 90 percent of the oil present in full-fat wheat germ.
Benefits
Wheat germ, a byproduct of the milling industry, is a source of highly concentrated nutrients such as vitamin E. The two-step process optimized in this study can be a viable environmentally benign alternative to conventional hexane extraction and easily incorporated into a wheat biorefinery system that would produce flour and wheat germ oil, which can be utilized in food and nutraceuticals and add value to the byproduct, wheat germ.
Economic Impacts
The capital cost of the new process would be significantly lower than the conventional wheat germ oil extraction processes currently used in industry. Simultaneous recovery of high nutritional value proteins and oil is expected to further improve the process economics. Additionally, the new process does not require hazardous chemicals and is simple to operate. Hence, this technique can easily be adapted by small processors targeting niche markets and operated by farmers’ cooperatives.
Continuing Work
No further work is needed to complete this project.
Publications
This project has resulted in a doctoral dissertation, two master’s theses and a paper in the Journal of American Oil Chemists’ Society and Biological Engineering Transaction. In addition, project information was presented during the 2012 FAPC Research Symposium and the 2012 Institute of Food Technologists’ Annual Meeting and Food Expo.
Funding
Funding for this project was provided by Hatch Act funds.
Collaborators
Nurhan Dunford, FAPC oil/oilseed specialist, was the primary investigator of this project. Other collaborators included Laith Fareed Al-Obaidi and Meizhen Xie, biosystems and agricultural engineering/food science doctoral students, and Michael Eisenmenger, food science master’s student.