Grinding and cooking dry-fractionated corn germ to optimize aqueous enzymatic oil extraction

Abstract

The many recent dry-grind plants that convert corn to ethanol are potential sources of substantial amounts of corn oil. This report describes an aqueous enzymatic extraction method to separate oil from dry-fractionated corn germ. The method is an extension of a method previously developed for wet-mill germ. Oil dispersed in lipid bodies throughout the germ was converted to oil droplets suspended in an aqueous solution and then to drops of oil large enough to be separated from the solution as a continuous, buoyant phase (free oil). A microwave oven was used to cook the germ to its highest temperature, just short of burning. Thereafter the germ was extracted using the method developed for wet-mill germ: mix the heated germ with water and cook it under pressure, followed by colloid milling and enzymatic digestion of the milled germ particles overnight. A foam fraction was removed from the digested dispersion by bubbling nitrogen through a short column connected to a mixing tank. The foam fraction was then centrifuged to separate free oil. An estimate of aqueous enzymatic extraction plant costs to extract 24 million kg of dry-fractionated germ per year [40 million gal/year ethanol], showed that income from the unrefined oil streams and a stream sending the rest of the germ to the fermentation process was roughly equal to the estimated operating cost, with an investment of $2.6 million. Recycle of the enzyme may reduce the estimated enzyme cost of $750,000/year.