THE INFLUENCE OF MOISTURE CONTENT AND COOKING ON THE SCREW PRESSING AND PRE-PRESSING OF CORN OIL FROM CORN GERM

Authors: Moreau, Robert; Johnston, David; Hicks, Kevin

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/28/2005
Publication Date: 8/30/2005
Citation: Moreau, R.A., Johnston, D., Hicks, K.B. 2005. The influence of moisture content and cooking on the screw pressing and pre-pressing of corn oil from corn germ. Journal of the American Oil Chemists' Society. Vol. 82, No. 11,p.851-854.

Interpretive Summary: Essentially all of the corn oil produced in the US is obtained by hexane extraction of the germ portion of the corn kernel. Corn germ is a co-product produced during both the wet milling of corn (a process that produces starch, sweeteners and ethanol) and the dry milling of corn (a process developed to remove the germ and bran to extend the shelf life of corn meal used in foods). Screw pressing has also been used to obtain oil from corn germ and from oilseeds, but because it is less efficient than hexane extraction, its use has been declining. A goal of our research is to develop alterative processes to obtain corn oil from corn germ, using water and enzymes and no hexane or other organic solvents. This project was undertaken to evaluate the possibility of using screw-pressing as a first step to remove some of the oil and to make the germ more accessible during the second step, enzymatic extraction. In this study we identified the optimal pretreatment and pressing conditions which resulted in screw-pressing yields of about 37% of the total oil from dry milled corn germ and 56% of the total oil from wet milled corn germ. Future studies will be undertaken to evaluate whether pre-pressing of corn germ can be followed up with a process that uses enzymes to increase the oil yields compared to the use of enzymes alone. The development of alternative processes such as these to obtain corn oil from corn germ could benefit some of the new dry grind ethanol plants, since many of them are developing methods to remove the germ before fermentation and obtain maximum value for their germ. Adding the on-site capability to enzymatically obtain corn oil from corn germ may be a way to increase profits for these new dry grind ethanol plants.

Technical Abstract: Samples of corn germ were obtained from a commercial corn wet mill (factory dried to about 4% moisture) and a commercial corn dry mill (undried, produced in the mill with about 13% moisture). The germ samples (200 grams each) were cooked for various times in either a conventional oven at 180ºC, or a microwave oven at 1500 W. Bench-scale single screw pressing was then performed. With the dry milled corn germ, no oil was extracted from the uncooked germ and a maximum yield of about 5% oil (26% of total oil recovery, TOR, relative to hexane extraction) was obtained by cooking the germ for 6.5 minutes in a conventional oven at 180ºC. A maximum yield of about 7% oil (37% TOR) was obtained by cooking it for 4.5 minutes in a microwave oven at 1500 W. With the wet milled germ, yields of about 7% oil (18% TOR) were obtained with the uncooked germ and yields increased to a maximum of about 22% oil (56% TOR) by cooking at 180ºC for 5 min or a maximum of about 17% oil (44% TOR) by cooking for 4 minutes in a microwave oven at 1500 W. These results indicate that microwave and conventional oven cooking are both effective pre-treatments before pressing. Microwave pre-treatment resulted in higher oil yields with dry milled germ and conventional oven pre-treatment resulted in higher oil yields with factory-dried wet milled corn germ.