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United States Department of Agriculture

Agricultural Research Service

Title: Methods for Decolorizing Corn Zein

item Sessa, David
item Eller, Fred
item Palmquist, Debra
item Lawton Jr, John

Submitted to: Industrial Crops and Products International Conference Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 24, 2003
Publication Date: August 1, 2003

Interpretive Summary: With the advent of increased production of ethanol from corn, it is now imperative that the co-products of ethanol production find new industrial outlets to alleviate the reliance on government subsidies. Zein is a protein derived from corn gluten meal, a co-product of ethanol produced by wet milling. Color of zein limits its use for some industrial products. Carotenoids are the color factors in zein. These have nutraceutical value. Hence, decolorizing zein will not only increase its usage in those industrial outlets where color is a deterrant but also the resulting carotenoid extracts have new value. We investigated a variety of processes for decolorizing zein and developed a new colorimetric assay to quantitate color removal. Our findings demonstrate that supercritical fluid extraction of zein wetted with ethanol will partially extract the carotenoids which are free of protein contaminant observed in all other processes investigated. The carbon dioxide and ethanol used in this process have the added feature of using by-products of ethanol production. A more complete decolorization can then be attained by further treatment of the decolorized product with activated carbon where activated carbon can be derived from biomass. These findings are of great importance to the ethanol industry that uses wet-milled corn co-products.

Technical Abstract: The yellow color corn and corn processing co-products is due to xanthophylls and carotenes. Colorless zein commands a premium price and the resulting extracted carotenoids possesses nutraceutical value. Our objectives were to devise methods for decolorizing zein and develop methodology to quantitate color removal. Decolorizing methods include: subcritical propane carbon dioxide and supercritical extractions of zein with ethanol entrainers. With ethanolic zein solutions: ultrafiltration/diafiltration on a tangential flow system; partitioning with toluene; column chromatography on Sephadex LH-60; batch treatment with activated carbon. Residual color removal was assessed by dissolving zein control or decolorized product in glacial acetic acid, filtering, and reading absorbances of dilutions at 448nm. Analysis of covariance from comparative logarithmic regressions of control zein and decolorized product dilutions was evaluated for use to determine degree of residual color. Because a covariate by treatment interaction was detected in treatments for supercritical fluid extractions, a mixed effects Analysis of Variance model comparing treatment method means at the mean level of the dilution factor was used. Results showed that subcritical propane extraction of zein with ethanol entrainer gave the least color removal. A commercial white zein possessed a similar degree of color removal as did ethanolic zein solutions partitioned with toluene. The most complete removal was achieved by extractions of zein from corn gluten meal followed by batch treatment of those extracts with activated carbon. However, recovered yield was lowest of all methods evaluated. Supercritical fluid extraction with carbon dioxide of zein with 15% ethanol entrainer for 15 minutes at 689.5 bar and 70 degrees C decolorized zein slightly less than did either the column chromatographic method with Sephadex LH-60 or a diafiltration of zein ethanolic solutions ultrafiltered through 500 D molecular weight cut-off membranes. These three methods gave excellent recoveries of decolorized zein product. The supercritical fluid method had the advantages of not needing to spray-dry the final product, did not require the copious volumes of ethanol needed for color removal by the other methods, and used the carbon dioxide and ethanol generated by the fermentation process.

Last Modified: 4/19/2015
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