|Craig Jr, James
Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2001
Publication Date: 5/21/2001
Interpretive Summary: Production of ethanol from corn has created a surplus of zein-rich by- products, distillers' dried grains and corn gluten, which are increasingly difficult to sell but which must be sold to make the ethanol plants viable. Zein commercially extracted from corn gluten costs 10 $/lb and only a few tons are produced each year; sales and use of greater amounts are inhibited dby its cost. Commercialization of less expensive, larger scale extraction of zein from corn will make production of zein coproducts an option for corn based ethanol plant owners. We have shown that zein extraction and sales can significantly reduce the overall cost of producing ethanol. Sale of extracted zein will enable U.S. corn producers to obtain and maintain higher return from the non-starch component of corn by separating non-feed products. To encourage investment in the corn extraction process, its market must be defined. An initial market for the corn-extracted zein, is replacing corn gluten-zein and other higher cost materials, as an edible coating or sheet-forming material. This article reports results of a batch re-extraction pilot plant method that simulates commercial continuous extraction. The results show the maximum concentration of native zein that can be directly dissolved in ethanol solutions. Potential zein extraction improvements are indicated.
Technical Abstract: Prolamine-rich, water insoluble proteins (zein) can be extracted from milled maize by vigorous mixing in heated ethanol solutions. In principle, high zein concentration solutions can be produced using a counter-current solids/liquid contactor, batch extraction is, however, less capable. The solid mass fraction of a milled grain slurry that can be pumped is 0.25 or less. Since the mass fraction of zein in maize is only about 0.05, the zei mass fraction of a batch extract will be less than 0.01. To increase the zein concentration the extract (liquid and fines) can be separated from the solid and used to extract fresh milled grain. This procedure can be repeated, but is constrained by losses of liquid with the extracted grain and by reductions of the extracting capacity of the extract due to the increasing solute or fines content. By examining the extract composition and yield it is possible to estimate the zein concentration that could be achieved in a continuous, countercurrent process. The centrifugate concentrations for a series of maize extractions in which the extracted maize and extract solution were cooled prior to centrifugation were analyzed. The analysis indicates that the protein content of the liquid centrifugate will not exceed 2% for any series of similar batch extractions, using ambient centrifugation to separate the maize from the extraction slurry. This contrasts with concentrations of zein of 10% or more achieved by extracting corn gluten.