GB2051104A

GB2051104A - Recovery of Xanthan Gum

Info

Publication number: GB2051104A
Application number: GB8016974A
Authority: GB
Original assignee: Merck and Co Inc
Current assignee: Merck and Co Inc
Priority date: 1979-05-24
Filing date: 1980-05-22
Publication date: 1981-01-14
Also published as: FR2457322A1; JPS55156594A; CA1141377A

Abstract

Xanthan gum is recovered by precipitation from fermentation beer. using alcoholic solvents at a temperature below 33 DEG C, generally 20-33 DEG C. The xanthan gum thereby produced has improved solubility especially in high salt solutions. As a result, the modified xanthan gum can be used in many instant dry-food mixes, which are improved by use of a more quickly soluble xanthan gum; or in certain explosive mixtures having high levels of ammonium nitrate.

Description

SPECIFICATION Recovery of Xanthan Gum This invention relates to the recovery of xanthan gum from xanthan gum beer. The latter, as is known, is prepared by fermenting the organism Xanthomonas campestris (NRRL B-1452) or a known proprietary mutant of it under a variety of fermentation conditions, or it can be obtained commercially.

Examples of representative patents teaching preparation of xanthan gum beer solutions and the precipitated gum itself are U.S. 3,232,929; U.S. 3,433,708; and U.S. 4,119,546. The gum has been isolated in lower (i.e. Cm~4) alkanols, or suitable alkanol-water azeotropes. Most conveniently, the precipitation has been carried out at relatively elevated temperatures, usually 38-430C.

The present invention is based on the unexpected discovery that lowering the temperature at which the precipitation process takes place so that it lies in the range 20 to 330C, preferably 24 to 290C, results in a novel modified rapidly soluble form of xanthan gum.

Normally, just before precipitation, the beer has been pasteurized (treated at about 990C). For the purpose of the invention, the beer is cooled to a temperature in the range 20 to 270C by circulating cooled water.

The alcohol precipitant can be any of those alcohols or alcohol-water mixtures normally used to precipitate xanthan gum from the beer. Preferably, C,~4 alkanols or aqueous azeotropes of such alkanols are used, and especially a isopropanol-water azeotrope having a constant boiling point in the range 37-440C is used. This azeotrope contains 83-85% isopropanol on a volume basis. In this invention, the alcohol is used during the precipitation step at a temperature in the range 20 to 270C.

Following the usual procedure, the volume of alcohol is 2 to 3 times. preferably 2.5 to 2.6 times, the volume of the beer.

The beer and the alcohol are pumped together in an impeller-driven coil, at the rate of about 57 litres per minute. The precipitated xanthan gum is recovered from the hardening coil.

As fermentation is generally done in batches, the precipitation step is also described as a batch operation, although it could easily be adapted to a continuous precipitation process if that were desirable.

As indicated above, production of the xanthan gum, the starting material in the practice of the present invention, by Xanthomonas campestris, NRRL B-1459, under a variety of fermentation conditions is well known. The present invention involves using an alcohol or its aqueous azeotrope at a lower temperature than hitherto to precipitate the xanthan gum in the fermentation broth (the mixture of unprecipitated xanthan gum and fermentation broth is called beer), which is independent of the biosynthetic pathway of the Xanthomonas or organism in its production production of xanthan gum.It is therefore apparent that the invention is operative using either NRRL B-i 459 or a commercially available mutant strain of Xanthomonas campestris known to produce xanthan gum in somewhat higher yields than NRRL B-1459. Since the function of the organism is merely to produce the starting material, the availability of this mutant strain is not significant to the practice of this invention. In addition, the beer can also be commercially obtained.

This invention is further illustrated by the following examples.

Example 1 4500 litres of fermentation beer containing about 41 60 litres of liquid xanthan gum was pasteurized at 990C by being pumped through a pasteurizing coil. It was then pumped through a cooling section until the cool beer temperature was 240C. (The pump rate for the entire system was 14.16 litres per minute). An isopropanol:water azeotrope, containing about 85% alcohol by volume, and a constant boiling point of about 430C is added at the mix pump. The temperature of the isopropanol solution was 230C: it was added at the rate of about 50 litres per minute. The mixture of beer and alcohol was then passed through a 114-litre hardening coil with discharge into a press throat.

Press discharge (crude precipitated xanthan gum) was dried through a single rotary drier set at 740C, milled and screened to pass 40 U.S. standard mesh. (The final product was made in batches and blended together in the dry powder state). The spent liquid was monitored; it contained about 62% isopropanol (volume) and its temperature was 25.50C.

For the purposes of comparison, an identically fermented batch was prepared. The beer was treated as usual, i.e., cooled to 430C, the alcohol solution was at 360C.

Example 2 A sample of the dry xanthan gum prepared as in Example 1 was evaluated in a standard NH4NO3 solution assay. The purpose of this assay was to determine the rate of viscosity development (and solubility) of the xanthan gum in concentrated NH4NO3 solutions, which are representative of commercial explosive mixtures.

Solutions were made as follows: an aqueous solution of NH4NO3 containing 76.8% NH4NO3 by weight was prepared. Dry xanthan gum was added so that final levels of xanthan gum was 0.36% by weight. Test temperature was 650C. Viscosity at one hour and at 3 hours was measured. In the system used, desirable viscosities are over 350 centipoises at one hour and in the range 700 to 800 centipoises or higher at 3 hours.

Results were obtained on samples as follows: Viscosity {centipoises) Example 2 1 hr. 3 hrs. % Solids A. control (no cooling, 360C alcohols, rotary dried) 312 684 89.3 B. one sample prepared according to Example 1, before blending 616 720 89.3 C. one sample prepared according to Example 1, after blending 440 728 88.7 Although samples can vary, the figures obtained illustrate that the low-temperature precipitation step affords, at the same solids level, a quantitatively different gum product having significantly increased viscosities at one hour and 3 hours when compared to a control sample.

Other uses for this improved xanthan gum are in instant-drink mixes, especially an orangeflavoured drink mix, or other flavoured beverages, soups, shakes, milk or soy milk products, cocoa mixes, salad dressings, instant desserts, instant imitation ketchup, calf-milk replacers, coated dry gravy-making pet food, and similar applications.

The improved xanthan gum produced by this invention is used at levels and in compositions generally known in the art; usually levels of xanthan gum in dry mixes is from 0.2 to 1.5% by weight (total weight basis).

When the xanthan gum is used in aqueous explosive mixtures, it is used at levels from 0.1 to 3% by weight. See U.S. Patent No. 3,326,733 for representative compositions.

Claims

1. A process for preparing xanthan gum, that comprises treating xanthan gum beer at a temperature in the range 20-330C with 2-3 times its volume of a C14 alkanol or an aqueous azeotrope of such an alcohol at a temperature in the range 20-270C and recovering the precipitated xanthan gum thereby produced.

2. A process as claimed in Claim 1, in which the alkanol is isopropanol.

3. A process as claimed in Claim 1, in which the aqueous azeotrope is isopropanol-water.

4. A process as claimed in Claim 3 in which the azeotrope temperature is about 230C.

5. The process of Claim 4, in which the volume of azeotrope used is about 2.5 times the volume of beer.

6. An aqueous explosive composition containing 0.13% by weight of a product obtained by a process as claimed in any one of Claims 1 to 5.

7. A dry food mix composition containing 0.21.5% by weight of a product obtained by a process as claimed in any one of Claims 1 to 5.

8. A process as claimed in Claim 1, substantially as hereinbefore described in Example 1 or 2.

9. Xanthan gum obtained by a process as claimed in any one of Claims 1 to 5 and 8.