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Microbial polysaccharides

Microbial polysaccharides. Xanthan Gum. A polysaccharide Used as food additive & rheology modifier. Production involves fermentation of glucose or sucrose by the bacterium, Xanthomonas campestris. STRUCTURE. M.W. varies from ~ 1 million - 50 million depending upon preparation Backbone:

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Microbial polysaccharides

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  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. 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. 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.

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