Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/31/2011
Publication Date: 10/31/2011
Citation: Yadav, M.P., Nunez, A., Hicks, K.B. 2011. Isolation, purification and identification of protein associated with corn fiber gum. Journal of Agricultural and Food Chemistry. 59:13289-13294. Interpretive Summary: “Corn fiber gum” (CFG) is a potential high value food ingredient we have prepared from “corn fiber”, an abundant and inexpensive byproduct of the corn wet milling ethanol industry. This new product has potential uses and high value because it has been shown to be a better emulsifier (compound that helps suspend oil in water) than gum arabic, an expensive and imported “gold standard” emulsifier used in the food industries. Gum Arabic is a “glycoprotein” that contains water loving (hydrophilic) polysaccharide and water-hating (hydrophobic) protein components on the same molecule, allowing it to interact with both oils and water which is required for good emulsifier activity. CFG has previously been shown to be primarily a hydrophilic polysaccharide. The scientific community has therefore wondered how such a polysaccharide could function as an emulsifier. Our research was done to find the answer to this puzzling problem. Our analysis results showed that there is actually a small amount of zein-like protein associated with CFG. Zein is known to be a “hydrophobic” (water-hating and oil-loving) protein that can associate with oils. This new finding explains how a hydrophilic (water-loving) polysaccharide like corn fiber gum, can act as an emulsifier and associate with oils. It is because of the hydrophobic character imparted by the presence of zein protein. This information will be useful to scientists and manufacturers who are endeavoring to produce and market CFG as a gum arabic substitute. These results may benefit corn farmers because new uses for corn byproducts will ultimately improve market for corn. It will also benefit the U.S. consumer and the U. S. economy since home-grown corn fiber gum containing this important protein can substitute for imported gum arabic in food products.
Technical Abstract: Corn fiber gum (CFG), an alkaline hydrogen peroxide extract of corn kernel milling by-product “corn fiber” is a proteinaceous arabinoxylan with a protein content ranging from ca. 2 to 9% by weight for the CFG samples isolated from different corn milling fiber sources. Several studies have suggested that protein associated with CFG play a significant role for its excellent emulsifying properties in oil-in-water emulsion system. Nevertheless, its protein identity has remained unidentified. CFG was deglycosylated by treating with trifluoromethanesulfonic acid (TFMS) and the resulting proteins were purified by passing through C18 cartridge. The proteins were separated and characterized by SDS-PAGE. The protein band from gel was treated with a proteolytic enzyme, chymotrypsin, which has a specificity pocket that fits an aromatic side chain of protein substrate for its cleavage. The resulting peptides were cleaned using C18 Zip Tip pipette tips and analyzed using matrix-assisted laser desorption/ionization with automated tandem time-of-flight mass spectrometry. The partial sequences derived from the mass spectrometry analyses of the resulting chymotryptic peptides are found to be similar to corn z 1 A alpha zein protein (major storage protein in corn endosperm) as queried against the primary sequences from the National Center for Biotechnology Information (NCBI) data base, which is the major storage protein in corn endosperm.