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United States Department of Agriculture

Agricultural Research Service

Research Project: AQUEOUS ENZYMATIC EXTRACTION OF CORN OIL AND VALUE-ADDED PRODUCTS FROM CORN GERM PRODUCED IN NEW GENERATION DRY-GRIND ETHANOL PROCESSES
2009 Annual Report


1a.Objectives (from AD-416)
Develop new environmentally safe aqueous/enzymatic processes to extract the edible oil from corn germ (obtained from new-generation dry-grind corn-to-ethanol plants) and develop processes to fractionate the de-oiled germ into value-added protein and carbohydrate coproducts, to improve the overall economics of making fuel ethanol in new-generation plants.


1b.Approach (from AD-416)
Corn germ from several new generation processes will be treated with mechanical (various forms of milling, homogenization and pressing), chemical (e.g. pH adjustment) and various enzymatic treatments, with the goal of causing the oil to coalesce and float upon centrifugation or other means of separation.


3.Progress Report
a. Intriguing recent beer research that may explain our foam separation process to separate corn oil from corn germ – We previously reported that foam from corn germ could be utilized to “float” corn oil. We suggested that proteins or peptides may coat the surfaces of the bubbles, stabilizing the foam. These corn germ proteins/peptides may be similar to proteins that were recently reported to occur in the foam (“head”) at the top of a glass of beer. In beer, these compounds were identified as fragments (peptides) of a protein whose function is to transfer lipids into and out of cells. These proteins are present in all cereals and they appear to adsorb on bubbles. Additional stability may result from other compounds which form bridges between adsorbed residues. Protein in a deoiled corn germ foam sample was analytically characterized showing it has a molecular weight consistent with a mixture of slightly reduced lipid transfer proteins and their aggregates (dimers). However, there are many other proteins in corn germ, including zein and oleosins, which have hydrophobic sequences that may also act as foam stabilizers.

b. Further characterization of two unique peptides from corn germ – Last year we identified and sequenced two peptides (one with eight amino acids and one with fourteen) from protease-treated corn germ fractions that inhibited Angiotensin Converting Enzyme (ASE). This year we synthesized both peptides and unfortunately, we found that neither inhibited ASE. This study indicates that protease treatment of corn germ produces ASE-inhibiting peptides with a size range of 700-1000 Daltons, however additional separation of this fraction has not yet identified the specific peptides that have ASE inhibitory properties.


4.Accomplishments
1. Developed an efficient process to produce oil bodies from corn germ. In the seeds of all higher plants, oil is stored in microscopic organelles called “oil bodies” which are each surrounded by a biological membrane comprised of phospholipids and proteins. Using dry milled corn germ, we modified a previously published method and achieved high yields of oil bodies from the corn germ. We then treated the oil bodies with several types of commercial enzymes and we identified several enzymes that resulted in good oil yields from the oil bodies. These results were then utilized to develop a bench-scale process that resulted in oil yields of up to 90% from isolated oil bodies. We are now evaluating the economics of this process to determine whether it is feasible to produce corn oil from corn germ via this two-step approach, with corn oil bodies as the intermediate step.

2. Developed a KG-scale aqueous enzymatic oil extraction (AEOE) process for dry-milled corn germ. Dry fractionated corn germ is less expensive to produce than wet milled corn germ. When we tried to use our oil extraction process with dry-milled germ, we were not able to extract any oil. The previous process was then modified by heating the germ prior to aqueous enzymatic oil extraction and we were then successful in extracting oil. A modified microwave oven and a pressure cooker allowed the germ to be heated sufficiently to obtain 1/2 the germ’s oil in the germ concentrated in a foam overflow containing only 1/6 the mass of the original dispersion. Centrifuging this concentrated fluid will require only 1/6 of the centrifugation that would be required to collect the oil from the entire germ dispersion. If 1.0 kg of oil is recovered from each bushel of corn converted by dry grind plants, producing 9 billion gallons of ethanol (nameplate capacity was nearly 12 billion gallons at the end of 2008) then 480 million gallons of oil could be recovered.


6.Technology Transfer

Number of Active CRADAs1

Review Publications
Moreau, R.A., Scott, K.M., Haas, M.J. 2008. The identification and quantification of steryl glucosides in precipitates from commercial biodiesel. Journal of the American Oil Chemists' Society. 85:761-770.

Dickey, L.C., Kurantz, M.J., Parris, N., Moreau, R.A. 2008. Separation of buoyant particles from an aqueous dispersion of corn germ particles using a bubble column. Chemical Engineering Science 63 (18), p.4555-4560.

Last Modified: 4/19/2014
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