Gelling compositions having a base of galactomannans and xanthan
This is a continuation of application Ser. No. 935,944 filed Aug. 25, 1978,  now abandoned. 
    
    
     This invention relates to the compositions which yield aqueous gels having a base of galactomannan and xanthan as well as to the gels obtained from these compositions and to the application of said gels. 
     Among the thickening agents currently in use, one well-known type consists of the galactomannans which are constituents of gums extracted from plants, e.g. guar gum, carob gum, tara gum, Espina corona gum. 
     Gelling agents which are also known include those obtained from glucides such as the sugars as a result of the action of a micro-organism; this is the case of xanthan, which is a polysaccharide obtained as a result of the action of bacteria of the Xanthomonas type. 
     It has been found possible to obtain gels of improved quality by associating xanthan and galactomannans; gels of this type have been described together with carob gum in U.S. Pat. Nos. 3,557,016, No. 3,726,690, U.S. Pat. No. 3,519,434, U.S. Pat. No. 3,623,868 as well as tara gum in French Pat. No. 2,119,365. These synergic effects have been reported in particular in the article by J. K. Rocks entitled &#34;Xanthan gums&#34; and published in the May, 1971 issue of &#34;Food Technology&#34;, volume 25, pages 22-31, in which it is stated that it was not possible to obtain such effects with guar gum. However, the association of xanthan which has been subjected to a heat treatment and of a guar gum has been described in French Pat. No. 2,193,074. 
     It has been unexpectedly observed during tests that, by carrying out preliminary deacetylation of xanthan, much stronger gels than those obtained from xanthan could be obtained from the different gums of galactomannans, irrespective of the conditions of salinity and pH of the gels. 
     Xanthan is a polysaccharide which can be considered as an acetyl ester of a polymer containing mannose, glucose and glucuronic acid in the form of potassium salt. The acetyl groups represent approximately 4.7% of the polysaccharide; an alkaline treatment makes it possible to eliminate these acetylated groups and to obtain a xanthan which is either partly or wholly deacetylated. The method of deacetylation has been described in particular in U.S. Pat. No. 3,000,790 which states that deacetylated xanthan makes it possible to obtain viscous solutions which are less sensitive to inorganic salts than natural xanthan. 
     The object of the invention arises from the discovery that gels of higher strength than the association of natural xanthan and galactomannan can be obtained from the association of deacetylated xanthan with a galactomannan as a result of a synergic effect. It has been observed in particular that, whereas the association of natural xanthan and guar gum produces by means of a synergic effect solutions having high values of viscosity up to the point of formation of a very weak gel, strong gels can be obtained by means of deacetylated xanthan. 
     The interaction just mentioned represents an important advantage of the invention. 
     A more complete understanding of the invention will be gained from the following examples and from the accompanying FIGS. 1 to 12 which represent curves of cohesion and rigidity of the salts as a function of the mixture ratio and of the influence of certain agents. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 shows curves of cohesion and rigidity, comparing xanthan and deacetylated xanthan in respect of different xanthan/carob gum ratios, using carob gum having a viscosity of 1300 cP. 
     FIG. 2 shows curves of cohesion and rigidity, comparing xanthan and deacetylated xanthan in respect of different xanthan/carob gum ratios, using carob gum having a viscosity of 40 cP. 
     FIG. 3 shows curves of cohesion and rigidity, comparing xanthan and deacetylated xanthan in respect of different xanthan/guar gum ratios. 
     FIG. 4 shows curves of cohesion and rigidity, comparing xanthan and deacetylated xanthan in respect of different xanthan/tara gum ratios. 
     FIG. 5 shows curves of cohesion and rigidity, comparing xanthan and deacetylated xanthan in respect of different xanthan/Espina corona gum ratios. 
     FIG. 6 gives result of rigidity measurements comparing xanthan and deacetylated xanthan in 50/50 mixtures with carob gum in respect of different doses of NaCl in the gel. 
     FIG. 7 gives result of cohesion measurements comparing xanthan and deacetylated xanthan in 50/50 mixtures with carob gum in respect of different doses of NaCl in the gel. 
     FIG. 8 gives result of rigidity measurements comparing acetylated xanthan with deacetylated xanthan. 
     FIG. 9 gives result of cohesion measurements comparing acetylated xanthan with deacetylated xanthan. 
     FIG. 10 gives results of cohesion measurements comparing acetylated xanthan with deacetylated xanthan in 50/50 association with carob gum in NaCl. 
     FIG. 11 gives results of cohesion measurements comparing acetylated xanthan with deacetylated xanthan in 50/50 association with carob gum in KCl. 
     FIG. 12 gives results of cohesion measurements comparing acetylated xanthan with deacetylated xanthan in 50/50 association with carob gum in CaCl 2 . 
    
    
     In these examples, natural xanthan is designated as acetylated xanthan in order to emphasize the difference with respect to deacetylated xanthan whereas the term xanthan can designate either of these two products. 
     The viscosity (η) of xanthans, of galactomannans or of the association of these latter is measured at 20° C. with a Brookfield viscosimeter at 20 rpm on a 1 percent solution and is expressed in centipoises (cP). 
     The gels of the xanthan-galactomannan association are obtained by dispersion in the cold state at the dose of 1 percent followed by heating between 75° and 95° C. and cooling. 
     These gels have been characterized by: 
     their rigidity: this term designates the force which is necessary to cause a piston to penetrate into the gel over a distance of 8 mm, as measured by means of the instrument known as a Bloom gelometer and expressed in grams; 
     their cohesion: this term designates the compressive strength as measured by means of a Kobe apparatus by adding weights of 200 g at intervals of 15 seconds and expressed in kilograms. 
     EXAMPLE 1--INCREASE IN SYNERGY BETWEEN XANTHAN AND CAROB GUM 
     There were employed an acetylated xanthan and a deacetylated xanthan having a viscosity of approximately 1000 cP and a carob gum having a viscosity of approximately 1300 cP. 
     A comparison between the acetylated xanthan and the deacetylated xanthan in respect of different xanthan/carob gum ratios is shown in Table I and in FIG. 1. 
     
                       TABLE I                                                     
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Ratio of                                                                  
xanthan                                                                   
       Rigidity (g)     Cohesion (kg)                                     
to carob                                                                  
       Acetylated                                                         
                 Deacetylated                                             
                            Acetylated                                    
                                    Deacetylated                          
gum    xanthan   xanthan    xanthan xanthan                               
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10/90  14        22         1.9     2.8                                   
20/80  23        41         3.3     4.4                                   
30/70  30        52         3.7     6.3                                   
40/60  34        53         2.9     7.5                                   
50/50  34        52         2.6     8.3                                   
50/40  27        50         1.8     8                                     
70/30  21        41         1.5     6                                     
80/20  13        25         1       2.8                                   
90/10   5        13         0.5     1.1                                   
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     EXAMPLE 2--INFLUENCE OF THE DEGREE OF POLYMERIZATION OF CAROB GUM 
     The increase in synergy is exhibited irrespective of the degree of polymerization of the carob gum. 
     The test is carried out with a carob gum having a viscosity of 40 cP and produces the results of Table II and of FIG. 2. 
     
                       TABLE II                                                    
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         Rigidity (g) Cohesion (kg)                                       
                     Deacety-         Deacety-                            
Ratio of xanthan                                                          
           Acetylated                                                     
                     lated    Acetylated                                  
                                      lated                               
to carob gum                                                              
           xanthan   xanthan  xanthan xanthan                             
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10/90       8        13       0.8     1.2                                 
20/80      18        28       1.4     2.4                                 
30/70      27        33       1.7     2.9                                 
40/60      28        35       1.6     3.6                                 
50/50      21        34       1.3     3.4                                 
60/40      19        30       0.9     2.8                                 
70/30      10        20       0.6     2.1                                 
80/20       9        11        0.35   1                                   
90/10       7         7       0.1     0.7                                 
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     EXAMPLE 3--IMPROVEMENT OF THE SYNERGY BETWEEN XANTHAN AND GUAR GUM 
     Use was made of an acetylated xanthan and a deacetylated xanthan having a viscosity of 1300 cP and a guar gum having a viscosity of 3500 cP. 
     A comparison between the acetylated xanthan and the deacetylated xanthan in respect of different ratios of xanthan to guar gum is shown in Table III and in FIG. 3. 
     
                       TABLE III                                                   
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                       Cohesion of                                        
        Viscosity of the solution                                         
                       the gel (kg)                                       
Ratio of xan-                                                             
          or of the ground gel                                            
                           Acety-   Deacety-                              
than to guar                                                              
          Acetylated                                                      
                    Deacetylated                                          
                               lated  lated                               
gum       xanthan   xanthan    xanthan                                    
                                      xanthan                             
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 5/95     5,400     6,500      liquid liquid                              
10/90     8,500     7,900      liquid liquid                              
15/85     7,800     7,400      gel not                                    
                                      liquid                              
                               measur-                                    
                               able                                       
20/80     7,500     9,000      liquid liquid                              
30/70     7,000     8,000      liquid 0.8                                 
40/60     6,000     8,200      liquid 1.3                                 
50/50     3,800     10,000     liquid 1.2                                 
60/40     3,300     15,000     liquid 1.4                                 
70/30     2,800     11,000     liquid 1.2                                 
80/20     2,300     9,000      liquid 0.8                                 
90/10     1,800     5,000      liquid 0.4                                 
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     EXAMPLE 4--IMPROVEMENT OF THE SYNERGY BETWEEN XANTHAN AND TARA GUM 
     Use was made of an acetylated xanthan and a deacetylated xanthan having a viscosity of 1000 cP and a tara gum having a viscosity of 600 cP. 
     A comparison between the acetylated xanthan and the deacetylated xanthan in respect of different ratios of xanthan to tara gum is shown in Table IV and in FIG. 4. 
     
                       TABLE IV                                                    
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         Rigidity (g) Cohesion (kg)                                       
                     Deacety-         Deacety-                            
Ratio of xanthan                                                          
           Acetylated                                                     
                     lated    Acetylated                                  
                                      lated                               
to tara gum                                                               
           xanthan   xanthan  xanthan xanthan                             
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10/90      11        17       1.3     2                                   
20/80      21        34       2.3     3.6                                 
30/70      27        41       2.6     4.6                                 
40/60      30        44       2.4     5.5                                 
50/50      26        43       1.9     5.8                                 
60/40      23        40       1.3     5.4                                 
70/30      18        30       1       4                                   
80/20      11        18       0.7     2.1                                 
90/10       6        10       0.3     1.2                                 
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     EXAMPLE 5--IMPROVEMENT OF THE SYNERGY BETWEEN XANTHAN AND ESPINA CORONA GUM 
     Use was made of an acetylated xanthan and a deacetylated xanthan having a viscosity of 1000 cP and an Espina corona gum having a viscosity of 800 cP. 
     A comparison between the acetylated xanthan and the deacetylated xanthan in respect of different ratios of xanthan to Espina corona gum is shown in Table V and in FIG. 5. 
     
                       TABLE V                                                     
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         Rigidity (g) Cohesion (kg)                                       
Ratio of xanthan     Deacety-         Deacety-                            
to Espina  Acetylated                                                     
                     lated    Acetylated                                  
                                      lated                               
corona gum xanthan   xanthan  xanthan xanthan                             
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10/90       8        15       0.7     1.1                                 
20/80      16        28       1.1     3                                   
30/70      22        35       1.7     4.3                                 
40/60      25        40       2.1     5.3                                 
50/50      27        42       2       5.4                                 
60/40      24        41       1.8     5                                   
70/30      18        30       1.4     3.9                                 
80/20      10        15       0.8     2.1                                 
90/10       5         8       0.3     0.7                                 
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     EXAMPLE 6 
     The use of gels in industry or in food usually calls for a medium containing salts and especially sodium chloride. 
     A study of the influence of electrolytes such as sodium chloride has been carried out with a 50/50 mixture of xanthan and carob gum. Three samples of acetylated xanthan have been compared with deacetylated xanthan in respect of different doses of sodium chloride in the gel. FIG. 6 gives the result of measurements of rigidity and FIG. 7 shows the result of measurements of cohesion. 
     These two figures show the superiority of gels having a base of deacetylated xanthan. However, by reason of the fact that the starting products do not necessarily have the same characteristics (Brookfield viscosity), a more rigorous example consists in starting from natural xanthan which is progressively deacetylated with 0.015 N sodium hydroxide (the deacetylation is followed over a period of time). 
     A comparison has been made between the characteristics of an acetylated xanthan and of three samples of more or less deacetylated xanthan obtained from this acetylated xanthan. FIG. 8 gives the result of measurements of rigidity and FIG. 9 gives the result of measurements of cohesion. 
     The advantage of deacetylation is readily apparent from the different proportions of sodium chloride and as a function of the degree of deacetylation. 
     EXAMPLE 7 
     A study of the influence of the electrolytes was carried out by comparing a sample of acetylated xanthan and a sample of deacetylated xanthan employed in a 50/50 association with carob gum in respect of different proportions of sodium chloride, potassium chloride and calcium chloride. FIGS. 10, 11 and 12 give the results obtained in the case of each of these three salts and show that the cohesion is higher with deacetylated xanthan in respect of each of these three salts. The same applies to the rigidity as shown in Table VI. 
     
                       TABLE VI                                                    
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Salt    g/l    Acetylated xanthan                                         
                              Deacetylated xanthan                        
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Standard                                                                  
        0      20             41                                          
reference                                                                 
NaCl    0.5    30             46                                          
        5      29             39                                          
        15     28             38                                          
KCl     0.5    31             50                                          
        5      35             48                                          
        15     37             45                                          
CaCl.sub.2                                                                
        0.5    21             26                                          
        2      21             27                                          
        5      22             27                                          
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     EXAMPLE 8--INFLUENCE OF THE USUAL ANIONS ON A GEL OF DEACETYLATED XANTHAN AND OF CAROB GUM 
     Ordinary anions do not produce any change in reactivity of deacetylated xanthan with respect to the carob gum. 
     Table VII gives the results obtained with a 50/50 mixture of deacetylated xanthan and carob gum to which are added various sodium salts in a quantity such that the proportion of Na +  with respect to the gum is constant and corresponds to 5 g/l of NaCl. 
     
                       TABLE VII                                                   
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Salt added      Rigidity (g)                                              
                          Cohesion (kg)                                   
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Standard reference                                                        
                20        5.5                                             
Chloride        30        3                                               
Carbonate       25        2.9                                             
Nitrate         32        3.2                                             
Acetate         28        3.3                                             
Sulphate        33        3.3                                             
Monosulphate    29        2.6                                             
Sodium citrate  30        2.6                                             
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     This table shows that the reactivity of deacetylated xanthan with the galactomannans is not affected by the various anions employed. 
     The gels of deacetylated xanthan plus galactomannans can have a practically infinite variety of consistency according to the galactomannan employed, the proportion of xanthan to galactomannan and the total dose of gum employed. These gels can consequently find an application in the food industry, for example in pork-meat gels (aspics) or jelly-type desserts, or in the technical field, for example in explosive gels or gels for air-treatment products.