Alginate

Question 1

Alginate in food structuring:

Answer 1

• Viscosifier
• Stabiliser / emulsifier
• Gelling agent

Question 2

Extraction of alginates from seaweed:

Answer 2

Macrocystis pyrifera (giant kelp) –> alkaline extraction (high pH)–> precipitation with acid or Ca2+–>alginate

Question 3

Properties of alginates (5), they depends on the building units:

Answer 3

1. Polymer of mannuronic acid (M) and guluronic acid (G)–> linear molecule.
2. Mw ca 100.000 Da (500 residues)
3. G and M present in M-M-M- ; G-G-G- ; and G-M-G-M blocks.
4. Relative abundance of G-, M- and GM blocks depends on seaweed origin.
5. Ratio and length of blocks determines functionality.

Question 4

Alginate G-G block form a gel with Ca2+, to make a strong gel, egg box model. Only with G-blocks and not with MG, M-blocks. TRUE OR FALSE?

Answer 4

TRUE

Question 5

Alginate in Food Applications

Answer 5

Broad applicability since alginate:
• Is able to form highly viscous solutions with good suspension-stabilising properties. Prevent to flow or to precipitate for example in dressings.
• Solution has fair stability at high temperature and pH because of the strength of the uronic acids, which cannot be broken easily.
• Is reactivity with Ca2+ ions enabling gel formation
• Gels have a good thermo-stability
Applications:
• Ice cream, sauces
• Desserts, syrups
• Bakery cream, pie filling

Question 6

Differences between alginate and pectin as hydrocolloids:

Answer 6

• Origin: alginate (sea weeds) pectin (plants, fruits and vegetables).
• What they are in common is the building blocks: alginate (mannuronic acid/ guluronic acid ), pectin (Galacturonic acid GalA) –> URONIC ACIDS.
• Strong gel with Ca2+: especially low methoxyl pectin to make calcium gel.
• Extraction: alginate (alkaline) and pectin (acid, high T, pH 1.5).
• Structural variation : alginate (ratio of M:G) and pectin (level of methyl esterification)

Question 7

How to explain differences in viscosity and/or gelling behaviour of 2 alginates having the same GulA:ManA ratio?

Answer 7

Alginates having longer GulA segments will be more sensitive to gel with Ca2+ than alginates having longer ManA or GM-GM sequences.

GulA:ManA ratio is not sufficient to predict the functional behavior of alginates.