Xanthan

Question 1

Which bacterial polysaccharides are in food structuring?

Answer 1

1. Xanthan
2. Gellan
   They are organized chemical structure due to presence of repeating units and controlled fermentation process.
3. Curdulan

Question 2

Which bacterial polysaccharides are produced by fermentation?

Answer 2

1. Xanthan
2. Gellan
3. Curdlan: B 1-3 linked glucan give quite a flexible structure.

Question 3

Structure of xanthan:

Answer 3

Microorganism: xanthamonas campestris. growing in nature in cabbage.
Structure: B-1,4 glucan where every second glucose has a side chain of mannose (acetyl group), glucuronic acid and mannose(pyruvate group).

Question 4

Xanthan conformation:

Answer 4

Transitional behaviour is influenced by

• Temperature
• Ionic strength
• pH
• Primary xanthan structure: Acetyl content and Pyruvate content

Question 5

Shear rate affects xanthan’s viscosity:

Answer 5

*When you do not have or very low shear (semi-ordered structures free flowing) you have a very high viscosity making xanthan an ideal viscosifier for dressings for example.
*When you add more shear to your solution by pouring, by swallowing you reduce the viscosity and you appreciate it when eating (ordered structure flowing).
There is a total different behaviour for for carboxylmethyl in Guar gum which shows a quite similar viscosity all over the range of different shears

Question 6

Effect of solvent conditions on xanthan conformation:

Answer 6

The conformation and consequently the fraction of unfolded xanthan strongly depends on the ionic strenght but also on the level of acetylation and pyruvylation.

Question 7

Xanthan in food applications?

Answer 7

Highly valued in food texturising since xanthan:
- Is quite soluble
- Is highly stable over wide pH and T range
- Exhibits highly pseudoplastic flow properties
- Shows moisture control in baked goods
- Shows strong interactions with galactomannans giving transparent, thermo-reversible gels.
Aplications:
- Batter coatings (onion rings, fish)
- Cakes, muffins, etc
- Dressings, cocktails and liquors
- Dairy products

Question 8

Gellan: main characteristics and applications

Answer 8

Produced by the bacteria Pseudomonas elodea
- Linear anionic heteropolysaccharide (ramannose)
- Broad-spectrum gelling agent
- Robust and flexible
-Highly functional at low concentrations
- Gelation depends on level of acylation and type and concentration of cations
Applications:
- Confectionary, jams, jellies, fabricated foods, waterbased gels

Question 9

Can you explain why xanthan, being a polymer with a cellulose-like backbone, is highly soluble and has good stabilising properties?

Answer 9

Although having a β-1-4 glucan backbone, xanthan also has short side chains enhancing solubility, especially when they are charged they may repel each other and the may prevent aggregation and association of the cellulose backbone .
The negative charges and the ‘apolar’ acetyl groups influence the molecular interactions, resulting in unique viscosity properties.