1. Microbial polysaccharides

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

3. STRUCTURE
M.W. varies from ~ 1 million - 50 million depending upon preparation
Backbone:
2 β-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.

4. The other mannose unit has an acetyl group at the 6 position.
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

5. Structure of Xanthan

6. 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.

7. 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

8. In frozen foods and beverages, creates the pleasant texture
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.

9. 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.