Polysaccharide composition and process for preparing same

#The present invention is directed to a method for the production of a novel heteropolysaccharide, having useful properties, from a pure culture of a certain Erwinia microorganism derived from a lactose-containing environment.

#Polysaccharides have extensive use in both food and non-food applications primarily as a result of their ability to modify the rheology, i.e., flow behavior, of aqueous systems. Examples of uses for polysaccharides include dispersants, thickeners, film forming agents, water retention agents, coagulants, colloids, lubricant/friction reducers as well as others.

#Commercially valuable polysaccharides are obtained by either recovery of gums from botanical sources, e.g., seaweeds, tree exudates, and plant seeds, or microbial fermentation broths, e.g., xanthan gum from fermentation of hydrolyzed corn syrup by Xanthomonas campestris. The process of production and recovery from fermentation broths generally involves the following steps:

#FIG. 1 is a graph illustrating the typical progress for a fermentation involving the preferred medium as described in Experiment 1 the specification.

#FIG. 2 is a chart illustrating the production of galactomannan polysaccharide from Erwinia sp. as a function of the carbohydrate source.

#FIG. 3 is a graph illustrating the steady shear viscosity of aqueous polysaccharide solutions across a variety of concentrations and shear rates at pH 7, 25.degree. C. and no salt present.

#The present invention is directed to the cultivation of a pure culture of the microorganism on a complex medium in an aerobic, submerged fermentation vessel. The particular strain of the microorganism involved in the present invention was discovered by the inventors and is identified by the following nomenclature: Erwinia sp. (E. sp.). A culture of the microorganism has been deposited with the American Type Culture Collection (ATCC) on May 15, 1990, having received ATCC No. 55046.

#The polysaccharide from E. sp. is characterized by a molecular weight of approximately 2.5.times.10.sup.6. Its main building blocks are mannose and galactose, which is a component of lactose in whey. E. sp. produces the novel galactomannan polysaccharide when cultured in presence of lactose, a component of whey, in addition to other carbohydrates.

#The microorganism was isolated from a soil sample of a Wisconsin farm field near Mineral Point, Wis., which had been regularly treated with whey.