Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Preparing compound containing saccharide radical
Reexamination Certificate
2001-04-13
2003-07-01
Prats, Francisco (Department: 1651)
Chemistry: molecular biology and microbiology
Micro-organism, tissue cell culture or enzyme using process...
Preparing compound containing saccharide radical
C435S101000, C435S274000, C536S114000, C536S123000, C536S123100, C536S127000
Reexamination Certificate
active
06586213
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved process for the clarification of aqueous xanthan solutions and the high purity xanthan gum produced thereby.
2. Related Background Art
Xanthan gums are hydrophilic polysaccharides which are obtained by the fermentation of appropriate nutrient media with microorganisms of the genus Xanthomonas. When dissolved in water in low concentration, xanthan gums impart a viscosity to the aqueous solution. The resulting viscosified solutions are used in a wide variety of industrial applications, such as in the manufacture of ingestible products, such as food products (sauces, ice creams, etc.), and in oil field drilling fluids. Xanthan viscosified solutions are particularly useful in applications where it is desirable to suspend solid materials in the aqueous medium.
During commercial preparation of most xanthan gums, the solid xanthan is recovered by precipitation from the fermentation broth in which it is made. Generally, it is not feasible to separate all extraneous fermentation solids before this precipitation step, so that the dried solid xanthan gum recovered in this manner normally contains some water insoluble solids, such as nonviable bacterial cells and other cellular debris. These solids, of course, do not dissolve when the xanthan is re-dissolved in water. While the presence of these solids is not objectionable in many cases, it is problematic in compositions or applications where a completely clear viscosified solution is desired.
Methods evaluated for overcoming this problem have included enzyme treatments. For example, U.S. Pat. No. 4,010,071 discloses a method of clarifying xanthan solutions by treating with an alkaline protease. EP 0078621 and GB 2111520 disclose a process for clarifying xanthan gum solutions by treatment of the solution with an acid or neutral protease, followed by increasing the pH of the solution to 8 to 13. U.S. Pat. No. 5,595,892 discloses a method for recovering and purifying xanthan gum from a fermentation broth by heating the broth to a temperature of 45° C. to 80° C. at a pH of 7.0 to 12.5, and then treating the solution stepwise with an alkaline protease and a lysozyme. EP 0549230, JP 8154695 and U.S. Pat. Nos. 5,679,556, 5,702,927, 5,705,368 and 5,994,107 disclose related methods wherein a fermentation broth is heated at a temperature of 45° C. to 70° C. at a pH of at least 9.0, followed by enzyme treatment, wherein the order of alkaline protease and a lysozyme enzyme treatments is interchangeable.
Japan Patent Appln. No.8 [1996]-154695 discloses another related method wherein a fermentation broth is heated at a temperature of 45° C. to 70° C. at a pH of at least 9.0, treated with a polyphosphate and subjected to treatment with an alkaline protease and a lysozyme. Polyphosphate was the only chelating agent useful in this process.
Although these methods may provide xanthan gum solutions with some improvement in clarity, these methods require several processing steps, sometimes under different processing conditions, which may result in increased manufacturing costs or due to the high pH treatments, cause degradation (de-acetylation and/or de-polymerization) of the xanthan gum. Accordingly, it would be advantageous to provide a simplified, mild and effective process for the preparation of clarified xanthan gum solutions and high purity xanthan gum.
SUMMARY OF THE INVENTION
This invention relates to a process for the preparation of a clarified aqueous xanthan gum solution. The process comprises the steps of treating a xanthan solution with at least one treating agent selected from a chelating agent, surfactant, organic acid or a mixture thereof, and treating with a protease enzyme or a lysozyme and a protease enzyme. The treating agent may be comprised of one or more chelating agents, one or more surfactants, one or more organic acids, or any mixture thereof. The enzyme treatment process may be conducted at a temperature of about 400° C. to about 800° C. at a pH of about 6 to about 8. This invention also relates to the purified solid xanthan gum, prepared by the process of this invention, which provides substantially clear xanthan gum solutions on dissolution in water. In addition, this invention relates to compositions containing the purified xanthan gum described herein.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with this invention, aqueous solutions of xanthan gum, containing suspended solids and fermentation cellular debris resulting from fermentation of Xanthomonas, may be clarified by a process comprising treating the xanthan solution with one or more chelating agents, one or more surfactants, one or more organic acids, or a mixture thereof, optionally with heating, and treating with a lysozyme and a protease enzyme. In another embodiment of this invention, aqueous solutions of xanthan gum may be clarified by a process comprising treating the xanthan solution with one or more chelating agents and treating with a protease enzyme. Advantageously, and in contrast to many prior art processes, the process of this invention does not require heating the xanthan gum solution at a pH of 9 or greater. Such high pH treatment typically results in partial or complete de-acetylation and may result in de-polymerization of the xanthan polysaccharide. Use of the near neutral pH processing conditions in the present invention provides a high purity xanthan gum product that retains substantially all of the characteristics and chemical integrity of the xanthan polysaccharide as produced by fermentation of the Xanthomonas bacteria. Advantageously, the high purity xanthan gum produced by the process of this invention possesses about 90% to 100% of the acetate concentration of the fermentation-derived xanthan gum (i.e., 10% or less of the acetate is lost during processing).
In one embodiment, the process of this invention may be conducted in a stepwise manner, wherein the xanthan solution is first treated with the chelating agent(s), surfactant(s), organic acid(s), or mixture thereof, then treated with the lysozyme and protease enzyme. In another embodiment, the process of this invention may be conducted in the stepwise manner wherein the xanthan solution is treated with chelating agent(s) then treated with a protease enzyme. Alternatively, the process may be conducted as a single operation wherein the xanthan solution is simultaneously treated with at least one chelating agent(s), surfactant(s), organic acid(s), or mixture thereof, and a protease enzyme or a lysozyme and a protease enzyme.
Advantageously, the process for producing clarified xanthan solutions described herein provides xanthan solutions that may be used, if desired after appropriate dilution, without any further chemical or mechanical treatment. The process of this invention provides for the substantially complete elimination of suspended cells from xanthan solutions. High purity xanthan gum may be isolated from these clarified solutions using conventional isolation procedures (e.g., precipitation with a non-solvent (e.g., isopropanol) followed by isolation of the precipitated product). Dissolution of this high purity xanthan gum in water provides a substantially crystal clear xanthan solution. A substantially crystal clear solution, according to this invention, has a light transmittance greater than about 90%. Light transmittance may be measured at any wavelength in the visible spectrum using conventional techniques and equipment (e.g., commercially available spectrophotometers). The light transmittance is typically measured at wavelengths of about 600 nm to 650 nm. Light transmittance may be determined for several types of xanthan gum solutions: untreated broth, partially treated broth (e.g., broth treated with only a chelating agent, an organic acid, surfactant, or a mixture thereof or broth treated only with a protease and/or lysozyme), treated broth, or reconstituted xanthan gum solutions (using xanthan gum isolated from treated broth). The substantially crystal clear solutions
DiMasi Don
Kobzeff Joseph M.
Mead Daniel E.
Talashek Todd A.
Banner & Witcoff , Ltd.
CP Kelco U.S. Inc.
Prats Francisco
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