The influence of moisture content and cooking on the screw pressing and prepressing of corn oil from corn germ

Samples of corn germ were obtained from a commercial corn wet mill (factory dried to about 3% moisture) and a commercial corn dry mill (undried, produced in the mill with about 13% moisture). The germ samples (200 g each) were cooked for various times in either a conventional oven at 180 degrees C or a microwave oven at 1500 W. Bench-scale single screw pressing was then performed. With the dry milled corn germ, no oil was obtained from the uncooked germ. A maximal yield of about 5% oil [26% of total oil recovery (TOR), relative to hexane extraction] was obtained by cooking the dry-milled germ for 6.5 min in a conventional oven at 180 degrees C before pressing. A maximal yield of about 7% oil (37% TOR) was obtained by cooking the dry-milled germ for 4.5 min in a microwave oven at 1500 W before pressing. 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 in a conventional oven at 180 degrees C for 5 min or a maximum of about 17% oil (44% TOR) by cooking for 4 min in a microwave oven at 1500 W. These results indicate that microwave and conventional oven cooking are both effective pretreatments before pressing. Microwave preheating resulted in higher oil yields with dry-milled germ, and conventional oven pretreatment resulted in higher oil yields with factory-dried wet-milled corn germ.