Microbial polysaccharides

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Microbial polysaccharides
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Xanthan Gum

• A polysaccharide
• Used as food additive rheology modifier.
• Production involves fermentation of glucose or
  sucrose by the bacterium, Xanthomonas campestris

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STRUCTURE

• M.W. varies from 1 million - 50 million
  depending upon preparation
• Backbone
• 2 ß-D-glucose units linked through the 1 and 4
  positions.
• Side chain
• 2 mannose units 1 glucuronic acid unit
• Linked to alternate glucose of the backbone at
  the 3 position.
• In all, thus, the chain has repeating modules of
  five sugar units.

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• 40-50 of terminal mannose units have a pyruvic
  acid group linked as a ketal to its 4 6
  positions.
• The other mannose unit has an acetyl group at the
  6 position.
• 2 of these chains aligns to form a double helix
• A rigid rod configuration
• High efficiency as a viscosifier of water

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Structure of Xanthan
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Preparation

• Inoculating a sterile aqueous solution of
  carbohydrate(s), a N2 source, dipotassium
  monohydrogen phosphate some trace elements
• Medium is well-aerated stirred
• Xanthan is produced extracellularly in the medium
• Final concentration of xanthan 3-5 by weight
• Fermentation for 4 days
• Precipitation of Xanthan from the medium by
  addition of isopropyl alcohol
• Dried and milled to give a powder that is readily
  soluble in water or brine.

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Applications

• Even 1 can greatly increase in the viscosity of
  a liquid
• In foods, used at 0.05 0.5.
• Viscosity decreases with high shear rates
  (mixing, shaking, chewing) Pseudoplasticity
• In salad dressings sauces
• Thicker at rest in the bottle to keep the mixture
  homogeneous
• Shear forces due to shaking thins it, so, easily
  poured
• After exiting the bottle, no shear force. So,
  thickens back clings to salad.
• Stable under a wide range of temperatures and pH

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• Helps to stabilize the colloidal oil and solid
  components against creaming.
• In frozen foods and beverages, creates the
  pleasant texture
• In toothpaste, serves as a binder to keep the
  product uniform
• In gluten-free baking, to give the dough / batter
  a "stickiness"
• Gluten in wheat to be omitted
• For thickening liquids for those with swallowing
  disorders, since it does not change the color or
  flavor of foods or beverages.

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• In the oil industry, to thicken drilling fluids
• Fluids serve to carry the solids cut by
  horizontal drilling bit back to the surface
• Also been added to concrete poured underwater, in
  order to increase its viscosity and prevent
  washout.
• In cosmetics, to prepare water gels usually in
  conjunction with bentonite clays.
• In oil-in-water emulsions to help stabilise the
  oil droplets against coelesence
• Has some skin hydrating properties.