Evaluation of green solvents for a sustainable zein extraction from ethanol industry DDGS

Abstract

Corn-ethanol industry in US alone generates about 35 Tg of Dried Distillers Grains with Solubles (DDGS) per year as co-product. DDGS is enriched with zein, a well-known corn protein. Vast potential of zein application in industries ranging from pharmaceuticals to bio-plastics resulted in a serious quest to develop process technologies for its extraction. A broad spectrum of primary, binary, ternary and tertiary solvents is available which can extract zein from DDGS. But most organic solvents are hazardous which limits their sustainable industrial-scale use. Our study evaluated green solvents: isopropanol, n-butanol, isobutanol, 2,3-butanediol (2,3-BDO), 1,4-butanediol, isoamyl alcohol, 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, acetic acid, lactic acid and ionic liquids [emim]Ac and [emim]Br for zein extraction. Isopropanol, 1,4-dioxane and 2,3-BDO showed promising results, with 75, 41 and 38% extraction efficiency, respectively. Operational parameters for efficient extraction such as temperature, pH and solvent-to-water ratio were subsequently optimized using response surface methodology for selected solvents. A combination of solvent to water volume ratio of 66:34, temperature of 77 °C and pH of 4.4 was found to be optimal for isopropanol, whereas 2,3-BDO worked best at solvent to water volume ratio of 73: 27, temperature of 85 °C and pH of 3.8. These results are encouraging and could lead to the development of green technology for efficient zein extraction.