Introduction polysaccharides

Question 1

Functionalities of polysaccharides:

Answer 1

• Thickening, increase in viscosity
• Gel forming properties
• Stabilisation: Emulsification, suspension, foam
• Film forming
• Aroma binding
• Glue properties
• Filling agent

Question 2

Properties of the polysaccharides:

Answer 2

1. Shape of the molecule: type, linkage and sequence of sugar residues.
2. Molecular weight: poly-disperse vs mono-disperse (all molecules with the same size).
3. Presence of charged groups: acids (COO-, SO4-, PO4-, pyruvate), esters(methyl-, acetyl-, amide-) stability (pH, T), number, distribution.
4. Solubility.
5. Ability to make junction zones.

Question 3

Sources of food hydrocolloids:

Answer 3

• Botanical: trees(cellulose), tree gum exudates (gum arabic), fruits(pectin), seeds(guar gum, locust bean gum, tara gum, starch)
• Algal: red seaweeds ( agar, carrageenan), brown seaweeds (alginate)
• Microbial: xanthan gum, gellan gum, curdlan, dextran, cellulose.

Question 4

How polysaccharides in solution behave?

Answer 4

The longer the molecule, the longer space occupies in solutions, and yielding and higher viscosity. But in contrast if you have a highly branched molecule with the same molecular weight you have much less space occupied in solutions, much lower viscosities.
When you have a charged molecule, the charges will repel the molecule you will have repulsion and more space occupies, higher viscosity.
**Conformation in solution strongly depends on primary structure of the polysaccharide

Question 5

Why is the viscosity of a pectin solution more depending on pH compared to a carrageenan solution?

Answer 5

The carboxyl groups of pectin will be fully protonated at low pH causing less repulsion of the molecule resulting in lower viscosity (neutral molecule). The sulphate group of carrageenan is charged at all pH’s.