Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/4/2009
Publication Date: 8/24/2009
Citation: Wang, Y., Tilley, M., Bean, S., Sun, X., Wang, D. 2009. Comparison of Methods for Extracting Kafirin Proteins from Sorghum Distillers Dried Grains with Solubles. Journal of Agricultural and Food Chemistry. 57(18):8366-8372. Interpretive Summary: Sorghum is an important crop in the Central Plains and ranks behind only wheat and maize in production. Sorghum is used worldwide as both animal feed and human food, but its major use in the US is animal feed. Increasing amounts are being used for fuel production; ~15% of the U.S. sorghum crop is fermented and used for ethanol production. The main coproduct from grain-based ethanol production is distillers dried grains with solubles (DDGS), of which more than 450 kilotons are generated annually from the fermentation of grain. DDGS is the high protein (~30-40% on average) residue left after starch is converted to ethanol. It serves as an inexpensive source of protein to supplement livestock feed. From 450 kilotons of sorghum DDGS, more than 136 kilotons of sorghum protein (on average) is available for use. As more ethanol plants are built in response to demand for fuel ethanol, there will be an increasing supply of DDGS with potential oversupply in regions with a high density of ethanol plants. Very little research has been conducted on extraction of sorghum proteins from DDGS. Objectives of this study were to compare various methods for extracting sorghum proteins from DDGS and characterize the chemical composition as well as physical and thermal properties, of the isolated proteins. We found that extraction conditions affected purity and thermal properties of the extracted protein. One method produced protein with 98.9% purity. This information will benefit future studies on functional properties of sorghum protein and use of sorghum protein from DDGS for industrial applications.
Technical Abstract: Use of coproducts generated during fermentation is important to the overall economics of biofuel production. The main coproduct from grain-based ethanol production is distillers dried grains with solubles (DDGS), the residue left after the majority of starch has been converted to ethanol. High in protein, DDGS is a potential source of protein for many bio-industrial applications such as adhesives and resins. The objective of this research was to characterize the composition as well as chemical and physical properties of protein from sorghum-based DDGS with various extraction methods including use of acetic acid, HCl-ethanol and NaOH-ethanol under reducing conditions. Several techniques - Fourier transform infrared spectroscopy, lab-on-a-chip electrophoresis, differential scanning calorimetry, size exclusion chromatography, reversed phase high-performance liquid chromatography and thermal gravimetric analysis - were used to evaluate structural, molecular and thermal properties. Extraction conditions affected purity and thermal properties of the extracted protein. Acetic acid and NaOH-ethanol produced protein with higher purity than protein extracted with the HCl-ethanol protocol. The acetic acid extraction protocol produced protein with the highest purity, 98.9%.