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Microbial polysaccharides

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Title: Microbial polysaccharides


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 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.

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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