Submitted to: Journal of Agriculture and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 4, 2007
Publication Date: July 4, 2007
Citation: Yadav, M.P., Johnston, D., Hicks, K.B. 2007. Characterization of corn fiber gums from coarse and fine fiber and a study of their emulsifying properties. Journal of Agriculture and Food Chemistry, 55,p.6366-6371. Interpretive Summary: Natural flavors in soft drinks are usually derived from essential oils that are not soluble in the water-based drinks. To ensure that the flavor is dispersed throughout the beverage and not just floating on the top, a substance called an emulsifier is added. The "gold standard" emulsifier for soft drinks is a material called "gum arabic" that is expensive and imported from unstable regions of the world which causes problems in the soft drink manufacturing industry. We are trying to make a new emulsifier from "home grown" materials to replace imported gum arabic. Previously, we reported a method to produce "corn fiber gum" (CFG), and studied its emulsifying properties. Corn fiber gum is not a chewing gum but rather is a complex carbohydrate material isolated from a low-value by-product of the industrial wet milling of corn. Our previous studies indicated that CFG was a better emulsifier than gum Arabic but we don't understand exactly how it functions or how it should be prepared to ensure a consistent, high quality product. In the present study this complex material was chemically characterized to understand its chemical composition and structure and to try to understand how the structure leads to its unique functionality. Also, to find its use in the food industries in the most economical way, experiments were done to find out the minimum amount of CFG needed to stabilize flavor oil droplets in oil-in-water emulsion systems. With this study we have found that CFG has capacity to stabilize (emulsify) 20 times its weight in oils in the soft drink model system. We also found that minor proteins and fats associated with this corn fiber gum might be partially responsible for its emulsification properties. These findings will be useful to commercial manufacturers who are trying to develop a new commercial product based upon corn fiber gum. If successful, it will lead to new markets for low-valued corn byproducts, which will benefit U.S. corn processors and corn growers.
Technical Abstract: The stabilities of orange oil emulsions stabilized with various concentrations of two different types of corn fiber gum (CFG-1 and 2) isolated from coarse (pericarp) and fine (endosperm) fiber from corn wet milling have been studied. CFG-1 and 2 were isolated from coarse and fine corn fiber by (a) sequential alkaline treatment and hydrogen peroxide bleaching and (b) re-extraction of the alkali treated residue by alkaline hydrogen peroxide, respectively. CFGs isolated from fine fiber contain comparatively higher amount of protein and lipid than the CFGs from coarse fiber. The emulsion stabilizing capacity of these CFGs was studied by preparing emulsions of oil-in-water by using high pressure homogenization and determining the stability by turbidity measurements of the diluted emulsions. The emulsion stabilities in all these studies increased with increasing gum concentration up to gum to oil ratio of 0.05 and after that it either levels off or changes very slightly. These results indicate that only 0.25% of CFG is required to make stable emulsion containing 5% orange oil under the experimental conditions used in this study. At this CFG concentration, CFG-2 from each fiber source was found to be a superior emulsifier that the corresponding CFG-1 from each source in a 10 days emulsion stability study at room temperature. The emulsion stability was also investigated by confocal scanning laser microscopy measurement and it was found that CFG-1 and 2 from both coarse and fine fiber made stable emulsions with average particle size less than 1 'm for 10 days at room temperature. Sugar composition analysis of CFGs from both sources indicated that they were typical galactoglucuronoarabinoxylans containing mainly 55-59% xylose, 29-36% arabinose and 4-6% galactose as neutral sugars and 3-5% glucuronic acid. Methylation analysis revealed a highly branched structure of all CFGs, in which only 16-25% of 1'4-linked xylose residues were not substituted at O-2 and/or O-3. Arabinose is present both as a terminal residue and at branch points.