XANTHAN VISCOSIFIED COMPOSITIONS AND PREPARATION THEREOF

Abstract: A xanthan gum viscosifier having enhanced hydration and dispersibility properties and xanthan viscosified compositions demonstrating improved thermal stability with retained low shear rate viscosity, is disclosed. Also disclosed is a process for improving the thermal stability and low shear rate viscosity of viscosified compositions and a process for the preparation of divalent cation-containing xanthan viscosified compositions using low shear mixing.

Description: TITLE XANTHAN VISCOSIFIED COMPOSITIONS AND PREPARATION THEREOF BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a xanthan gum viscosifier having enhanced hydration and dispersibility properties and xanthan gum viscosified compositions having improved thermal stability with retained low shear rate viscosity. In addition, this invention relates to a process of preparing viscosified compositions using low shear mixing and improving the thermal stability and low shear rate viscosity of compositions by incorporating a divalent cation- containing xanthan product . Related Background Art Xanthan gum is a biosynthetic water-soluble polysaccharide produced during the aerobic fermentation of carbohydrates by Xanthomonas bacteria. The fermentation medium also contains trace elements and other nutrients. Xanthan' s unusual rheological properties make it useful in oil well drilling fluids, as a viscosity control additive, in secondary recovery of petroleum by water flooding, and as a stabilizer, emulsifier and thickener in foods, cosmetic preparations, pharmaceutical vehicles and as a suspension agent in numerous industrial applications (See. Encyclopedia of Polymer Science and Engineering 901-918, Ilnd Edition (1989) John Wiley & Sons) . Fermentation of a xanthan- roducing micro-organism on a continuous or batch basis gives a viscous broth or beer containing the desired gum. Various techniques are available for the recovery of the xanthan gum from the broth, with precipitation being, by far, the most common. The methods for precipitating xanthan gum from aqueous solution include precipitation using a water- miscible organic solvent which is a non-solvent for xanthan gum; for example, by addition of acetone, methanol or isopropanol ; using an aqueous alkaline solution to precipitate a calcium or other divalent metal salt of the polymer; precipitation using a water- iscible organic solvent and a sodium or potassium metal salt, for example, by addition of ethanol and potassium chloride; precipitation at acid pH of an aluminum salt of the polymer; or precipitation as a quaternary ammonium salt of the polymer. A widely used method for the recovery of xanthan gum is precipitation using about 60% to about 75% by weight of an azeotropic isopropanol-water solution added to the broth. This gives xanthan gum as a salt of the cations already present in the broth, which is predominantly a mixed potassium and sodium xanthan salt. Although xanthan is a widely used versatile viscosifying agent, limitations on its use exist. High shear mixing is often necessary to disperse and hydrate conventional xanthan gums. Such high shear mixing equipment is expensive and may not be available in remote locations (e.g., ocean oil drilling/recovery operations) . Exposure of conventional xanthan gums to high temperatures reduces the ability of the xanthan to maintain the viscosity of compositions. Additionally, the ability of xanthan to maintain the viscosity of a composition, especially at elevated temperatures, must often be enhanced by the addition of salts, such as sodium chloride or potassium chloride. Increasingly, environmental conditions or regulations preclude the use of these electrolytes. Accordingly, commercial exploitation of xanthan would be enhanced by the development of a xanthan product that is more readily dispersible and that demonstrates enhanced re-hydration and thermal stability, particularly under low-salt use conditions. SUMMARY OF THE INVENTION The present invention relates to viscosified compositions comprising a readily re-hydratable and thermally stable divalent salt-containing xanthan gum. In addition, this invention also provides a process for improving the thermal stability of viscosified compositions and an improved process of hydrating and dispersing a xanthan gum comprising using a divalent cation-containing xanthan gum. The divalent cation- containing xanthan used in this invention may be prepared by precipitating xanthan from an aqueous solution, comprising adding an effective amount of a divalent salt and an organic solvent to the solution to precipitate the xanthan. The divalent salt is preferably an alkaline earth metal salt, and most preferably is a water soluble calcium salt. The process for precipitating xanthan comprises the following steps: (a) producing xanthan in a fermentation broth by aerobic fermentation of a bacterium, and (b) precipitating the xanthan by adding a divalent salt and an organic solvent. BRIEF DESCRIPTION OF THE DRAWINGS In describing the overall invention, reference will be made to the accompanying drawing, FIG. 1, showing a plot for the salt-aided precipitation of xanthan. DETAILED DESCRIPTION OF THE INVENTION The term "xanthan" as used herein means the extracellularly produced biogum made by the heteropolysaccharide-producing bacterium of the genus Xantho onas by whole culture fermentation, under a variety of conditions, of a medium comprising a fermentable carbohydrate, a nitrogen source, and other appropriate nutrients well known to those skilled in the art. It has been discovered that divalent cation-containing xanthan products demonstrate unexpectedly improved properties. The divalent cation-containing xanthan demonstrates improved re-hydration rates and divalent cation-containing xanthan viscosified compositions demonstrate retention of viscosity, particularly low shear rate viscosity, after exposure to elevated temperatures. As used herein, "low shear rate viscosity" is the viscosity of a composition measured at a shear rate of less than about 100 sec" 1 , as measured using a Fann Model 35 or a Fann Model 50 viscometer (sold by Fann Instruments, Houston, Texas) or a shear rate of less than about 1 sec '1 , as measured using a Brookfield LV Series Viscometer (sold by Brookfield Engineering, Middleboro, Massachusetts) . The xanthan useful in this invention is a divalent cation-containing xanthan that contains a significantly greater concentration of divalent cations relative to potassium and sodium ions, present in the fermentation broth. The divalent cation-containing xanthan useful in the process of this invention contains at least 1% by weight divalent cation, wherein the divalent cation is the cation of a divalent salt. Preferably, the divalent cation-containing xanthan contains at least 2% by weight of the divalent cation of a divalent salt. More preferably, the divalent cation-containing xanthan contains at least 3% by weight of the divalent cation of a divalent salt. Typically, the xanthan contains about 3% by weight calcium and less than 1% by weight of each of potassium and sodium. One embodiment of this invention provides a process to improve the thermal stability of viscosified compositions. It has been determined that compositions viscosified with a divalent cation-containing xanthan retain a significant amount of initial viscosity, particularly low shear viscosity, after exposure to heat for prolonged periods of time or after exposure to a series of heating and cooling cycles. Moreover, the divalent cation-containing xanthan compositions retain significantly more of their initial viscosity than comparable conventional xanthan compositions. This improvement in the retention of viscosity provides for the preparation of compositions having improved thermal stability. The enhanced thermal stability of the divalent cation- containing xanthan compositions can provide benefits in a wide range of applications, and may be particularly useful for the preparation of products wherein the xanthan-containing product may be subjected to heat either during the processing or manufacturing of the product or during the use of the product. Advantageously, the divalent cation- containing xanthan composition may be incorporated into any of a variety of aqueous compositions to improve the thermal stability thereof. The divalent cation- containing xanthan may be used to improve the thermal stability of conventional salt-containing aqueous compositions, and may be especially useful for the preparation of thermally stable products having very low salt concentrations (e.g., products prepared using potable water) . In addition, because the thermal stability of these compositions is improved compared to conventional xanthan-viscosified compositions, reduced concentrations of the divalent cation-containing xanthan may be used to provide equi-viscous compositions. The viscosifying functionality of the divalent cation-containing xanthan is maintained for longer periods of time than conventional xanthan, particularly, under harsh temperature conditions. Another embodiment of the present invention provides for a process of improving the preparation of viscosified compositions by using a divalent cation- containing xanthan having enhanced hydration and dispersion properties to viscosify aqueous compositions. The divalent cation-containing xanthan hydrates more rapidly than conventional xanthan gums. Advantageously, because of the improved hydration and dispersion properties of the divalent cation-containing xanthan, low shear mixing may be used to disperse the xanthan in aqueous compositions to form desired viscosified compositions. As used herein, "low shear mixing" is a rate of stirring or mixing of a composition that is equivalent to less than about 1,000 rp using a Lightnin' type Mixer (sold by Cole Parmer Instrument Co., Vernon Hills, Illinois) equipped with a 3 -prong propeller-type blade. One having skill in the art will appreciate that other types and models of commercially available mixers may be used to provide stirring rates that are equivalent to the above- described "low shear mixing" rate. Typically, high shear mixing is used to promote hydration of xanthan that is slow to hydrate. It has been discovered that divalent cation-containing xanthan hydrates and disperses rapidly in water, especially in sea water, and that the hydration and dispersion of the xanthan may be accomplished without resort to high shear ' mixing. Use of low shear mixing may be required for the preparation of shear-sensitive compositions, containing materials that may be degraded by exposure to high shear mixing (e.g., biological materials or particulate materials) . Low shear mixing may also be required for the preparation of compositions that are prepared in remote locations, where access to high speed mixing equipment may be limited. Small-scale food and industrial manufacturers may be required to use low shear mixers/mixing to prepare their products because of the high cost of high shear mixing equipment. The improved hydration and dispersion of the divalent cation-containing xanthan would be a benefit to these manufacturers. It is understood that the divalent cation-containing xanthan used in this invention may be also be used in combination with other functional ingredients to extend the functionality of those ingredients. The divalent cation-containing xanthan, when used in combination with other functional ingredients, may impart the above-described thermal stability and hydration/dispersion benefits to these compositions, thereby increasing the utilities for these compositions. The divalent cation-containing xanthan may be present in an amount of about 10% to about 90% of the total amount of divalent cation- containing xanthan/functional ingredient mixture used in the composition. Functional ingredients that may advantageously be used in combination with or blended with the divalent cation-containing xanthan may be other conventional ingredients that are used to influence texture, viscosity or other functional characteristics of compositions, such as sodium- or potassium-containing xanthan, welan gum, gellan gum, rhamsan gum, carrageenan, carboxymethyl cellulose, polyacrylamides, polyacrylates, microcrystalline cellulose, pectin, gum arabic, galactomannans, including locust bean gum, tara gum, and guar gum, and glucomannans, including konjak, and the like. For example, the divalent cation-containing xanthan may be combined or blended with conventional sodium- or potassium xanthanate to viscosify a composition. A preferred starting material for preparation of the divalent cation-containing xanthan is an aqueous Xanthomonas hydrophilic colloid solution, a xanthan- containing fermentation broth, prepared by the bacterium Xanthomonas campestris. While Xanthomonas campestris is the preferred bacterium, nevertheless related species of Xanthomonas that also produce a hydrophilic colloid may be utilized. Such other species are, for example, Xanthomonas begoniae, Xanthomonas malvaceraum, Xanthomonas carotae, Xanthomonas incanae, Xanthomonas phaseoli , Xanthomonas vesicatoria, Xanthomonas papavericola, Xanthomonas translucens , Xanthomonas vesicatoria, and Xanthomonas hedrae. Preferably, the aqueous xanthan-containing fermentation broths contain about 1 to 7% of xanthan gum. Divalent salts and an organic solvent may be used to insolubilize and precipitate xanthan from a xanthan- containing fermentation broth in a readily recoverable form. The process comprises addition of an aqueous solution of a divalent salt and an organic solvent to an aqueous xanthan solution to effect separation, by precipitation, of the xanthan hydrocolloid from the other materials present in the fermentation broth. The process for precipitating xanthan comprises the following steps: (a) producing xanthan in a fermentation broth by aerobic fermentation of a bacterium, and (b) precipitating the xanthan by adding a divalent salt solution and an organic solvent. According to this process, an effective amount of a water-soluble divalent salt is added to an aqueous xanthan solution (e.g., the xanthan- containing fermentation broth) to assist the precipitation of the xanthan. Advantageously, the use of divalent salts significantly reduces the amount of organic solvent required to precipitate xanthan compared to conventional xanthan precipitation, which relies on the organic solvent, alone, to effect xanthan precipitation. The preferred water-soluble divalent salts are alkaline earth metal salts, especially calcium salts, although other divalent salts may also be employed, such as magnesium or barium salts. Use of divalent calcium salts was determined to be the most effective in reducing the amount of organic solvent required to effect precipitation of xanthan. Exemplary preferred divalent salts include calcium chloride, calcium propionate, calcium acetate, calcium nitrate or mixtures thereof. Preferably, calcium propionate, calcium acetate or calcium nitrate are used to precipitate the xanthan. Typically, the divalent salt is added to the xanthan solution in the form of an aqueous salt solution and may be added at elevated temperatures (at or above the fermentation temperature) , at room temperature, or at reduced temperatures (above 32°F (0°C) ) . Useful aqueous salt solutions are aqueous saturated salt solutions or aqueous solutions containing about 10% to about 70% by weight of the divalent salt. The aqueous divalent salt solution is added to the aqueous xanthan solution in an amount of about 1 gram to about 25 grams of divalent salt per liter of xanthan solution. Typically, the divalent salt is added to the aqueous xanthan solution in an amount of about 1 gram to about 10 grams of divalent salt per liter of solution. The concentration of divalent salt required to precipitate the xanthan will depend not only on the volume of xanthan broth, but on the concentration of xanthan in the broth and, as described above, the specific divalent salt used. The divalent salt concentration required for xanthan precipitation is related to the number of moles of carboxyl substituents of the xanthan molecules in the solution. Typically, one calcium ion is required for every two xanthan carboxyl substituents. For example, a one liter sample of xanthan broth containing 3% xanthan will contain 30 g of xanthan. There is approximately 1 mole of carboxyl substituents for every 640 g of xanthan, therefore there are about 0.047 moles of carboxyl substituents in a 3% xanthan solution. Accordingly, 0.023 moles of Ca +2 ions would be required to precipitate all of the xanthan. Since the molecular weight of calcium nitrate is 164.1 g/mol, 3.85 grams of calcium nitrate would preferably be used to precipitate the xanthan from a 3% xanthan solution. The xanthan is precipitated using an alcohol, a ketone or any other organic solvent that is miscible with water. The organic solvent may conveniently be used in any commercially available form, e.g., as an anhydrous solvent, as a mixture of alcohols or ketones (e.g., isomeric mixtures) or as a mixture of the organic solvent in water (e.g., azeotropic mixtures). Preferably, the alcohol is methanol, ethanol, propanol, isopropanol (isopropyl alcohol) , butanol or mixtures thereof. More preferably, the alcohol is ethanol or isopropanol and the ketone is acetone. To precipitate the xanthan, the organic solvent may be added to the aqueous xanthan solution in a ratio of at least 0.5:1, that is, 0.5 volumes of organic solvent for each volume of xanthan solution. Preferably, the organic solvent is added to the aqueous xanthan solution in a ratio of about 0.6:1 to about 3:1. Generally, to effect precipitation of the xanthan, the divalent salt solution is added prior to the addition of the organic solvent, however, this order of addition may be interchanged. Precipitation of xanthan may be accomplished by addition of the organic solvent in an amount of at least 0.5 volumes of organic solvent per volume of xanthan solution. Precipitation is preferably conducted using an aqueous xanthan solution containing 1 to 7% xanthan. To effect precipitation of the xanthan, a calcium salt solution is added to the xanthan solution (fermentation broth) , to provide a xanthan solution containing about 1 to about 10 grams of salt per liter of solution, followed by addition of isopropanol in an amount of about 0.6 to about 3.0 liters isopropanol per liter of xanthan solution. Preferably, part of the process to produce xanthan involves pasteurization of the xanthan-containing fermentation broth. The pasteurization serves a number of purposes including, increasing the viscosity of the xanthan, sterilization of the xanthan and destruction of unwanted enzymes. Pasteurization of the broth may be conducted using any conventional pasteurization technique. Preferably, the pasteurization is conducted at a temperature from about 155°F (70°C) to about 250°F (120°C) for about 0.1 to about 5 minutes and more preferably from about 175°F (80°C) to about 230°F (110°C) for about 0.1 to about 5 minutes. Preferably, the aqueous xanthan solution used for xanthan precipitation by addition of a divalent salt and an organic solvent is an aqueous pasteurized xanthan solution. Accordingly, the process for precipitating xanthan may also comprise the following steps: (a) producing xanthan in a fermentation broth by aerobic fermentation of a bacterium; (b) pasteurizing the xanthan-containing fermentation broth; and (c) precipitating the xanthan by adding a divalent salt and an organic solvent. Preferably, the process for precipitating xanthan further comprises the step of cooling the pasteurized xanthan solution prior to the addition of a divalent salt and an organic solvent. More preferably, the pasteurized xanthan solution is cooled to a temperature less than about 140°F (60°C) . The xanthan precipitate may be separated or isolated from the supernatant using conventional techniques, e.g., by decanta ion. The isolated xanthan may be further treated as desired, for example, to remove excess solvent and/or improve the granularity of the xanthan product. It is considered to be within the ordinary skill of one in the art to subject the isolated xanthan product, described herein, to any conventional post- fermentation/post- isolation treatment, as desired. Aging of aqueous viscosified compositions containing a calcium-containing xanthan ("calcium xanthanate") at temperatures of up to 225°F (107°C) provided viscous compositions that demonstrated retained levels of low shear rate viscosity. It has been discovered that compositions viscosified with calcium xanthanate demonstrate superior retention of low shear rate viscosity compared to compositions viscosified with conventional potassium- or sodium-containing xanthans. After exposure to temperatures of about 175°F (79°C) to about 190°F (88°C) , compositions viscosified with the calcium-containing xanthan possessed viscosities that were 2 to greater than 3 times higher than compositions viscosified with a sodium-containing xanthan. Moreover, viscosified compositions of this invention exposed to temperatures as high as 225°F (107°C) continued to demonstrate good retention of low shear rate viscosity. Additionally, the divalent cation-containing xanthan, prepared by the above-described process, contains reduced quantities of impurities. Specifically, the calcium xanthanate produced using the above-described process contains an ash content that is 1-2% lower than that found in the xanthan precipitated using conventional techniques. The improved thermal and hydration properties of the divalent cation-containing xanthan compositions may be used to prepare stable, viscosified compositions for a wide range of applications. These viscosified compositions may be conventional xanthan-viscosified compositions, and especially, may be heat-treated compositions or compositions prepared by low shear mixing. The process of preparing the compositions of this invention comprises incorporating an effective amount of a divalent cation-containing xanthan into a composition to impart a desired viscosity to that composition. The xanthan may be added in very low amounts (e.g., about 0.025% by wt. to provide only enough viscosity to impart mouthfeel, for example, to a beverage) or may be added in significantly higher amounts (e.g., about 2% by wt. to provide very thick, viscous gels, such as milling fluids for oil field operations) . Accordingly, the divalent cation- containing xanthan compositions of this invention may contain about 0.025% to about 2% divalent cation- containing xanthan by weight of the total weight of the composition. The divalent cation-containing xanthan may be incorporated into a composition in any conventional manner. It is understood that the divalent cation-containing xanthan may be directly incorporated into a composition to viscosify that composition, may be incorporated into an ingredient that is used to viscosify a composition or may be admixed with a composition which forms a viscosified composition upon addition of water. It is considered to be within the ordinary skill of one in the art to prepare any of the herein-described viscosified compositions using the divalent cation- containing xanthan as a viscosifier. The divalent cation-containing xanthan may be particularly useful as a viscosifier and suspending agent for the preparation of aqueous oil field drilling fluids, milling fluids, workover fluids, completion fluids and stimulation fluids. The enhanced thermal stability of the divalent cation-containing xanthan, particularly the calcium xanthanate, provided these fluids with improved viscosity stability under the high temperature operating conditions typically encountered during oil well operations. Moreover, the ability of the divalent cation-containing xanthan to maintain the viscosity of compositions, without added salt, provides for the preparation of aqueous oil field drilling fluids, milling fluids, workover fluids, completion fluids and stimulation fluids that are particularly suitable for use in environmentally sensitive or environmentally protected areas. The improved hydration of the divalent cation-containing xanthan in high ionic conditions may provide for the preparation of enhanced performing aqueous oil field drilling fluids, workover fluids, completion fluids and stimulation fluids in remote locations, where access to high speed mixing equipment may be limited. Because the divalent xanthan is more readily dispersed using low shear mixing than conventional xanthans, the resulting fluids may have enhanced viscosity and viscosity stability compared to fluids prepared with conventional xanthan. The enhanced thermal stability provided by the divalent cation-containing xanthan may provide benefits in a wide range of food applications. Specifically, the enhanced thermal stability provided by calcium xanthanate in low ionic conditions can provide benefits in a wide range of food applications, particularly where the food may be subjected to high temperature treatments. Ultra high temperature (UHT) processing is used with ever- increasing frequency in the food industry. Products that have traditionally been processed for very short periods of time, but at high temperatures of about 75°C to about 100°C, such as dairy products, beverages, and processed eggs, are now often processed using UHT technology, where the processing temperatures are increased to about 100°C to about 150°C. UHT coupled with aseptic packaging has been successfully applied to continuous-flow processing of liquids and fluids containing small particles. More recently, interest has focused on aseptic processing of low-acid viscous foods containing large particulates. UHT processing may possibly degrade conventional xanthan gums resulting in the loss of some of its functional properties such as suspension or viscosity. The improved thermal stability of divalent cation- containing xanthan may provide for the preparation of viscosified foods that may be treated using UHT processing, and especially any products sold in ultrahigh temperature processed tetra-paks. The divalent cation- containing xanthan may be used conventionally to viscosify foods and may be used to prepare viscosified foods that are subjected to heat treatment or that are prepared using low shear mixing. The divalent cation-containing xanthan may be particularly useful in food products such as dairy products, such as ice cream, ice milk, frozen yogurt, milk-based drinks (milk shakes and th.e like) , yogurt- based drinks, salad dressings, bakery products, such as cakes, muffins and cookies, doughs, such as ready-to- bake refrigerated doughs and sweet doughs, batters, such as cake batters or coating batters, egg products, such as liquid egg products or processed eggs, beverages, such as fruit drink beverages, tortillas, pet foods, including high salt pet foods, canned products and moist or semi-moist pet foods that may be extruded and heat and/or pressure treated. The improved hydration of the divalent cation-containing xanthan in high ionic conditions can provide benefits in a wide range of food applications, particularly where the food product may be, or may preferably be prepared using low shear mixing conditions. The divalent cation-containing xanthan may be useful for the preparation of high salt foods, such as hot sauce, soy sauce, soy sauce based products, marinades, salad dressings and other high salinity sauces. The divalent cation- containing xanthan may be particularly useful in personal care products such as toothpaste, skin lotions, hair care products, and cosmetics. Heat treatment is often used in the manufacture of these products, particularly to solubilize waxy components in the formulations. The divalent cation-containing xanthan provides enhanced resistance to degradation during heat processing and therefore, retains more of its functional properties (viscosifying ability) in the final product. Curing compounds, polishes and air freshener gels are also often subjected to heat processing and may benefit from the improved thermal stability provided by the divalent cation-containing xanthan. Jet printing of textiles requires the use of dyes and inks having good viscosity control during steam setting. Calcium xanthanate retains viscosity control during high temperature treatment and would be especially useful for preventing migration of the dyes and inks, providing sharper definition of the dye images and enabling the preparation of highly detailed pattern designs. Divalent cation-containing xanthan may also be a useful component in coatings, paints, ceramic glazes and binding formulations (additives to paints and coatings) that are subjected to high temperatures (e.g., baking). Oven cleaners contain viscosifiers to prevent run-off of the cleaner to maintain contact of the cleaner with the oven surface. Oven cleaners, especially cleaners requiring heating, containing a divalent cation- containing xanthan may retain their viscosity longer than typical xanthan, providing longer contact time of the cleaner with the oven surface and enhanced cleaning effectiveness. Divalent cation-containing xanthan may also be a useful component in tire sealants, that are often subjected to temperatures of 150°F (65.5°C) or more and must remain fluid in the tire until a puncture occurs. The enhanced thermal stability of the divalent cation-containing xanthan may be able to maintain homogeneity of the suspension of the active ingredients for extended periods of time. Accordingly, this invention provides viscosified compositions, and a process for preparing the same, comprising using low shear mixing to disperse a thermally stable divalent cation-containing xanthan, wherein the divalent cation-containing xanthan is present in an amount effective to impart a desired viscosity to the composition. This invention provides for the preparation of conventional xanthan-containing compositions and particularly, the preparation of compositions wherein the use of conventional xanthan has been unsatisfactory, either due to insufficient thermal stability or due to hydration difficulties. The improved viscosified compositions of this invention possessing enhanced thermal stability and/or prepared using low shear mixing include, but are not limited to food products, such as dairy products, including ice cream, ice milk, frozen yogurt, milk-based drinks (milk shakes and the like) , yogurt-based drinks, salad dressings, bakery products, such as cakes, muffins and cookies, doughs, such as ready-to-bake refrigerated doughs and sweet doughs, batters, such as cake batters or coating batters, egg products, such as liquid egg products or processed eggs, beverages, such as fruit drink beverages, tortillas, high salt foods, such as hot sauce, soy sauce, soy sauce based products, marinades, and other high salinity sauces, pet foods, including high salt pet foods, canned products and moist or semi-moist pet foods that may be extruded and heat and/or pressure treated, dyes, inks, toothpastes, skin lotions, hair care products, cosmetics, curing compounds, polishes, coatings, paints, ceramic glazes binding formulations, oven cleaners, tire sealants, oil field drilling fluids, workover fluids, completion fluids, stimulation fluids, and especially any of the above products that may be sold in tetra-packs or products otherwise pasteurized using ultrahigh temperature treatment. The Examples which follow are intended as an illustration of certain preferred embodiments of ' the invention, and no limitation of the invention is implied. Xanthomonas Fermentation Broth Preparation of xanthan fermentation broths (solutions) are well known in the art. For example, the preparation of such broths is described in U.S. Patent No. 4,758,356, U.S. Patent No. 5,194,396, U.S. Patent No. 3,232,929, U.S. Patent No. 3,338,792 and U.S. Patent No. 4,868,293, the disclosures of which are hereby incorporated by reference herein. EXAMPLE 1 The amount of a constant boiling mixture (CBM) /azeotropic mixture of isopropanol-water (85 wt% isopropanol, 15 wt% water) required to effect precipitation of xanthan from a fermentation broth was determined in the presence and absence of salt using viscosity titration. A Xanthomonas campestris fermentation broth containing about 4% xanthan was prepared. Approximately 2.7 volumes of CBM was required per volume of broth to effect precipitation of the xanthan in the absence of salt. With efficient mixing of the CBM and broth, the amount of CBM required to effect precipitation was reduced to 1.75 volumes per volume of broth. In the presence of 20 g/1 of Na 2 S0 4 , KC1 or CaCl 2 , the ratio of added CBM volume to broth volume was reduced to 1.05:1, 1.0:1 and 0.6:1, respectively. The salt being evaluated was added to the fermentation broth as a homogeneous, concentrated aqueous solution in deionized water. EXAMPLE 2 Using broth from a single Xanthomonas campestris fermentation broth containing about 4% xanthan, precipitation titrations with CBM (85 wt% isopropanol, 15 wt% water) were carried out at different calcium and sodium salt concentrations. The titration curves for these broths containing calcium acetate ("CaAc"), calcium propionate ("CaProp") and sodium acetate ("NaAc") are shown in FIG. 1. Calcium (divalent) salts were found to be more effective than sodium (monovalent) salts for precipitation. EXAMPLE 3 A xanthan-viscosified composition containing calcium xanthanate, obtained by precipitation using calcium nitrate and isopropanol/water, was prepared by mixing 2.0 g of the calcium xanthanate (CaX) in 350 ml of tap water at 11,500 rpm for 20 minutes using a Fann Multi- mixer. Two comparative xanthan-viscosified compositions containing FLOWZAN ® , and FLODRILL ® (sodium xanthanate products of the Archer Daniels Midland Corporation, Decatur, Illinois) were prepared using the same procedure. The initial viscosity of each xanthan composition was measured at 60 rpm, 6 rpm and 3 rpm (102.2 sec "1 , 10.22 sec "1 and 5.11 sec "1 , respectively) using a Fann 35A viscometer (sold by Fann Instruments, Houston, Texas), and at 0.6 rpm and 0.3 rpm (0.12 sec "1 and 0.06 sec '1 respectively) using a Brookfield LV Series Viscometer (sold by Brookfield Engineering, Middleboro, Massachusetts) . Each xanthan composition was placed in a glass container and placed in an oven heated to a temperature of 175°F (79°C) for 16 hours. The oven was equipped with an apparatus that permitted turning or rolling of the containers during the heating period. The xanthan compositions were cooled to 75 °F (24°C) and the viscosity of each composition was measured. The results presented below reflect the viscosity of the compositions after heating compared to the initial viscosity, expressed as a percentage thereof . % Retention of Low Shear Rate Viscosity Shear Rate CaX Flowzan Flodrill 10.22 sec "1 98.6% 84.6% 76.25 5.11 sec '1 98.4% 77.8% 72.6% 0.12 sec "1 89.2% 45.5% 37.6% 0.06 sec "1 85.4% 37.8% 29.1% EXAMPLE 4 Xanthan-viscosified compositions were prepared as described in Example 3, above. In this Example, the compositions were heated to a temperature of 190°F (88°C) for 16 hours, cooled to 75°F (24°C) and subjected to viscosity measurement, as described in Example 3. The retained viscosity of these samples is presented below. % Retention of Low Shear Rate Viscosity Shear Rate CaX Flowzan Flodrill 10.22 sec "1 85.9% 69.2% 75.0% 5.11 sec "1 83.5% 63.9% 69.9% 0.12 sec "1 62.9% 21.4% 32.9% 0.06 sec "1 57.3% 16.5% 25.2% EXAMPLE 5 A calcium-xanthanate composition was prepared and analyzed as described in Example 3, above. In this Example, the composition was heated to a temperature of 190°F (88°C) for 1 hour (Cycle I) , cooled to 90°F (32°C) , re-heated to 190°F (88°C) for 1 hour (Cycle II) , then cooled to 90°F (32°C) . The retained viscosity of these samples over the course of this heat treatment is presented below. % Retention of Low Shear Rate Viscosity Shear Rate Cycle I Cvcle II 90°F 102.2 sec "1 99.0% 98.1% 132.7% 10.22 sec "1 92.4% 85.4% 146.5% 5.11 sec "1 93.0% 95.8% 163.7% EXAMPLE 6 A calcium-xanthanate composition was prepared and analyzed as described in Example 3, above. In this Example, the compositions were heated to a temperature of 225°F (107°C) for 1 hour (Cycle I) , cooled to 90°F (32°C) , re-heated to 225°F (107°C) for 1 hour (Cycle II) , then re-cooled to 90°F (32°C) . The retained viscosity of these samples over the course of this heat treatment is presented below. % Retention of Low Shear Rate Viscosity Shear Rate Cycle I Cycle II 90°F 102.2 sec "1 43.5% 34.0% 76.2'- 10.22 sec" 1 43.8% 36.7% 61.8 ! 5.11 sec "1 37.9% 48.2% 62.9 s EXAMPLE 7 Pasteurization of a fermentation xanthan broth was conducted by heating the broth to a temperature of 90°C for about 4 minutes. A control xanthan sample was prepared by precipitation of the xanthan from a room temperature (about 70°F (21°C) ) pasteurized xanthan solution by addition of 2.5 volumes of 90% isopropanol/10% de- ionized water per volume of xanthan solution. A calcium xanthanate was prepared by adding an aqueous solution of calcium chloride dihydrate (4.17 g CaCl 2 in about 10 ml deionized water) to 600 ml of xanthan solution at 90°C. This calcium- containing xanthan was then precipitated by addition of 90% isopropanol/10% de- ionized water. The precipitated fibers of both the calcium xanthanate and the control were dried and milled under the same conditions. The dried products were tested for hydration rate in sea water. Each xanthan product sample (0.86 g) was added to 300 ml of sea water and stirred at 800 rpm for 1 hour using a Lightnin' Mixer (sold by Cole Parmer Instrument Co., Vernon Hills, Illinois) equipped with a 3 -prong propeller-type blade. The viscosity of the sea water solution was measured using a Fann 35 viscometer at a rotational speed of 3 rpm (5.11 sec "1 ). The dial reading was recorded. The solution was then mixed for an additional 45 minutes using a Hamilton Beach Blender at 11,000 rpm. The viscosity at 3 rpm (5.11 sec '1 ) was remeasured. The ratio of the initial to final reading indicates the relative hydration rate of the products. Sample Initial Final Hydration Control 3.5 17 21 Ca Xanthan 11 16.5 67 EXAMPLE 8 A second experiment was conducted under conditions similar to those described in Example 7 except that the calcium chloride dihydrate was added to the pasteurized broth after the broth was cooled to room temperature, prior to precipitation. The following hydration results were obtained: Sample Initial Final % Hydration Control 10 20 50 Ca Xanthan 15 18 83 Other variations and modifications will be obvious to those skilled in the art. This invention is not limited except as set forth in the claims.

Claims: WE CLAIM: 1. A process for preparing a viscosified composition having improved thermal stability, said process comprising the step of adding a divalent cation- containing xanthan to a composition in an amount effective to viscosify the composition. 2. The process according to claim 1, wherein the divalent cation-containing xanthan contains at least 1% by weight divalent cations . 3. The process according to claim 1, wherein the divalent salt- containing xanthan is prepared by a process comprising the step of precipitating the xanthan from an aqueous solution by adding an effective amount of a divalent salt and an organic solvent to the solution to precipitate the xanthan. 4. The process according to claim 3 , wherein the xanthan is produced in a fermentation broth by aerobic fermentation of a bacterium of the genus Xan thomonas. 5. The process according to claim 3, wherein the divalent salt is selected from the group consisting of calcium propionate, calcium acetate, calcium nitrate or mixtures thereof. 6. The process according to claim 3, wherein the organic solvent is ethanol or isopropanol. 7. The process according to claim 3 , wherein the organic solvent is acetone. 8. The process according to claim 3, wherein the aqueous xanthan solution contains about 1 to 7% xanthan gum, the organic solvent comprises isopropanol and the divalent salt is present in the amount of about 1 to about 25 grams per liter of solution. 9. The process according to claim 1, wherein the divalent cation-containing xanthan gum has enhanced hydration and dispersion properties. 10. The process according to claim 1, wherein said viscosified compositions is selected from the group consisting of food products, dairy products, ice cream, ice milk, frozen yogurt, milk-based drinks, milk shakes, yogurt-based drinks, salad dressings, bakery products, cakes, muffins, cookies, ready-to-bake refrigerated doughs, sweet doughs, cake batters or coating batters, egg products, processed eggs, beverages, fruit drink beverages, tortillas, hot sauce, soy sauce, soy sauce based products, marinades, high salinity sauces, pet foods, canned pet foods, moist or semi-moist pet foods, dyes, inks, toothpastes, skin lotions, hair care products, cosmetics, curing compounds, polishes, coatings, paints, ceramic glazes binding formulations, oven cleaners, tire sealants, oil field drilling fluids, workover fluids, completion fluids, stimulation fluids, and viscosified products pasteurized using ultrahigh temperature treatment. 11. An improved process of hydrating and dispersing a xanthan gum, said improvement comprising the step of hydrating and dispersing a divalent cation- containing xanthan gum. 12. The process according to claim 11, wherein said divalent cation-containing xanthan gum is dispersed using low shear mixing. 13. The process according to claim 11, wherein the divalent cation-containing xanthan contains at least 1% by weight divalent cations. 14. The process according to claim 11, wherein the divalent cation-containing xanthan is prepared by a process comprising the step of precipitating the xanthan from an aqueous solution by adding an effective amount of a divalent salt and an organic solvent to the solution to precipitate the. xanthan. 15. The process according to claim 14, wherein the xanthan is produced in a fermentation broth by aerobic fermentation of a bacterium of the genus Xanthomonas. 16. The process according to claim 14, wherein the divalent salt is selected from the group consisting of calcium propionate, calcium acetate, calcium nitrate or mixtures thereof. 17. The process according to claim 14, wherein the organic solvent is ethanol and isopropanol. 18. The process according to claim 14, wherein the organic solvent is acetone. 19. The process according to claim 14, wherein the aqueous xanthan solution contains about 1 to 7% xanthan gum, the organic solvent comprises isopropanol and the divalent salt is present in the amount of about 1 to about 25 grams per liter of solution. 20. A viscosified composition comprising a thermally stable divalent cation-containing xanthan gum in an amount effective to viscosify the composition, wherein the composition retains low shear rate viscosity after heating. 21. The composition according to claim 20, wherein the composition is a food product. 22. The composition according to claim 20, wherein the composition is a dye or ink. 23. The composition according to claim 20, wherein the composition is selected from the group consisting of toothpaste, skin lotions, hair care products, and cosmetics. 24. The composition according to claim 20, wherein the composition is selected from the group consisting of curing compounds, polishes, coatings, paints, ceramic glazes and binding formulations. 25. The composition according to claim 20, wherein the composition is an oven cleaner. 26. The composition according to claim 20, wherein the composition is a tire sealant. 27. The composition according to claim 20, wherein the composition is an oil field drilling fluid. 28. The composition according to claim 20, wherein the composition is a workover fluid. 29. The composition according to claim 20, wherein the composition is a completion fluid. 30. The composition according to claim 20, wherein the composition is a stimulation fluid. 31. The composition according to claim 20, wherein the composition is a dairy product. 32. The composition according to claim 20, wherein the composition is a salad dressing. 33. The composition according to claim 20, wherein the composition is soy sauce. 34. The composition according to claim 20, wherein the composition is a bakery product. 35. The composition according to claim 20, wherein the composition is an egg product. 36. The composition according to claim 20, wherein the composition is a beverage. 37. The composition according to claim 20, wherein the composition is a pet food.

Inventors: BOUSMAN WILLIAM S DI, CARTER PATRICIA G, COFFEY MITCHAEL D, SEHEULT JAMES M, TALASHEK TODD A, WINSTON PHILLIP, BOUSMAN, WILLIAM, S. DI, CARTER, PATRICIA, G., COFFEY, MITCHAEL, D., SEHEULT, JAMES, M., TALASHEK, TODD, A., WINSTON, PHILLIP
Applicants: MONSANTO CO, MONSANTO COMPANY
Application year: 2000
Main classification: C08L5
IPC codes: C08B37, C08L5, C12P19