VIÑA DEL MAR - CHILE   Año 1   Numero 1   Agosto de 2007

The Xantan and the Alginate

The Xantan gum

   The Xantan, is a Polysaccharide, that is to say a complex Carbohydrate made up of several sugars, it is produced by a called bacteria Xanthomonas Campestris that infects to some tropical plants, there are dedicated industries to the production and handling of these bacterias to obtain the Xantan, but they are very scarce, the Xantan is a powder similar cream colour to the obtained of the algae, it is water soluble hot and cold, it forms very viscous solutions with little quantity, also its non different viscosity a lot with the temperature, the pH or concentration of salts (potassium chloride for example). The salts spread to solidify the gels.

   The xantano molecule consists of a main chain of D-glucopiranosilo with connection 1-4, like in the cellulose. To the chain lateral chains of trisacharid are annexed composed by residuals of D-manopiranosile and of D-glucopiranosiluronic acid. The manosile residuals with connection 1-2 have substitutes 6-or-acetyl. An average of approximately half of the terminal groups of the D-manosile they have substitutes 4,6-or-(1-carboxietilideno), for example the pyroacemic acid with connection 4,6 acetal. It is assigned as formula I average C32.34H49.94O28.34Na1.38. AND they summarize, this molecule has: D-glucose, D-mannose and D-glucoronic acid, similar compounds to those of the molecule of Alginate, that is to say that is a compound polymerized because several of these molecules (monomers) they unite to form the rubber, what gives him partly their viscosity. This is their molecular structure the n that is to the side it means that they are many molecules that unite among if to give the compound:



   This Rubber Uses it as preservative together with other rubbers in the perforation fluids, these fluids also pass through perforations that there are among the kitchen knives of the mouthpieces of the diamond drills to cool the drill and to lubricate the surfaces in contact with her, to clean the bottom of the well maintaining the particles in suspension, some of those rubbers are that of Guar and that of locust because they increase the viscosity from the fluid when mixing and they don't form gels, single viscous solutions.

   The Xantan also has very high molecular weights among 1200 to 1800 Kd, the same as the alginates that have up to 1500 Kd or more, alone that these last ones if they change its viscosity with the temperature depending on the molecular weight.

The Alginate

   The algae synthesize the alginate initially as a polymer of manuronic acid that later on modify transforming manuronic units in guluronic units. The end product contains areas formed by guluronic, areas formed by manuronic and areas with guluronic and alternate manuronic. The areas of manuronic acid are almost plane, with a structure similar to a tape, while those of guluronic acid present a structure with incoming and salient.

   It should be kept in mind with these zones is that the relative content of each one of these blocks depends to a lesser extent on the type of seaweed and on the conditions of its growth. Whereas the block formed by alternating guluronic and manuronic always represents around 1/3, the one of poliguluronic and polimanuronic changes to much table 1: it indicates that the alginates of the seaweed indicated with yellow like pyrifera Macrocystis, ascophyllum and lessonia, have many zones of manuronic acid MMMM, for that reason they form elastic gels, with low tendency to the syneresis (this is the tendency to lose I eliminate and to diminish the volume of the gel, is contracted) and capacity to undergo deformation; however the others as Laminaria Hyperborea has many zones GGGG of guluronic acid, for that reason form rigid gels, with low capacity of union of water and tendency to the syneresis.



Table 1

% M
Contents alginate
(% seeweeds dry)
  Laminaria hyperborea
25 27
  Laminaria digitata
20 26
  Macrocystis pyrifera
  Ascophyllum nodosum
26 - 28
  Lessonia nigrescens
  Ecklonia maxima


   Factors that will have to consider the producers:

   1. Molecular weight: Whichever greater it is p.m. of the alginate, more viscous are his solutions. The producers can control the p.m. of alginate compounds (polymerization degree) varying the conditions of extraction and manufactures. Products with GP between 100 and 1000 units are offered generally, that give viscosities in the rank of 10-1 000 mPa.s (solutions to 1%).

   2. Concentration: The commercial alginates can be obtained in different degrees from viscosity - high, average and low - the one that can be controlled varying the concentrations used within a more or less close rank.

   3. Temperature: The solutions of alginates behave just as other fluids in the dependency of viscosity with the temperature: within certain rank, the viscosity of such solutions decreases approximately 2.5% by each degree of increase in the temperature. The process is reversible, being able the solution to return to its initial viscosity by cooling. Nevertheless, if the solutions of alginates stay to high temperatures (50º C) during extensive periods, viscosity decreases irreversibly due to a depolymerization process; behavior that will have to consider very during the storage of obtained products industrially.

Articulo Eugenia León