Improved methods for decolorizing corn zein

Abstract

The yellow color of corn and corn processing co-products is due to xanthophylls and β-carotene. Colorless zein commands a premium price and the resulting extracted carotenoids possess nutraceutical value. Our objectives were to devise methods for decolorizing zein and develop methodology to quantify color removal. Decolorizing methods include: subcritical propane and supercritical fluid extraction with carbon dioxide of zein with ethanol entrainers; ultrafiltration/diafiltration on a tangential flow system; partitioning with toluene; column chromatography on Sephadex LH-60; batch treatment with activated carbon. Residual color was assessed by dissolving zein control or decolorized product in glacial acetic acid, filtration, and reading absorbances of dilutions at 448 nm. Analysis of covariance from comparative logarithmic regressions of control zein and decolorized product dilutions was evaluated to determine the extent of residual color. Because, a covariate by treatment interaction was detected in treatments for supercritical fluid extractions an Analysis of Variance model comparing treatment method means at each dilution factor level 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 residual color as did ethanolic zein solutions partitioned with toluene. Almost 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 with this procedure. Supercritical fluid extraction with carbon dioxide of zein with 15% ethanol entrainer for 15 min at 68,950 kPa and 70 °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 the 5000 Da molecular weight cut-off membrane. These three methods gave excellent recoveries of decolorized zein product. The supercritical fluid method has the advantages of no need to spray-dry the final product and does not require the copious volumes of ethanol needed for color removal by the other methods. This method would utilize the carbon dioxide and ethanol byproducts generated by the fermentation process used for producing ethanol.