1. Gelling polysaccharides
What is a gel
Look at
Alginates
Pectin
Carrageenans
Synergy
Xanthan
LBG
Mechanisms for gelation
Notes can be found on ;
sbw5f/APPS/APPS/WINAPPS/Data/
Slides and Lectures/SEHill/INDEX.HTM
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2. X Gelation of proteins Polysaccharides
Said to occur when a small amount of solid is dispersed in a relatively large amount of solvent (usually water), by the property of mechanical rigidity.
Defined as a protein aggregation phenomenon – attractive and repulsive forces are so balanced that a well ordered tertiary network or matrix is formed.
Protein gels are composed of three dimensional matrices or networks of interwined, partially associated polypeptides in which water is entrapped.
Is a continuous network of macroscopic dimensions immersed in a liquid medium and exhibiting no steady flow.

3. Gels X

4. Structure and Gels Retorted gels 0.4% locust bean gum/0.4% carrageenan
Total 0.8% polysaccharide
Egg white ~12% protein

5. Gel structures Aggregates of spherical particles
Framework of Rod-like particles
Physical gel with crystalline junctions
Chemical gel -covalent junctions

6. Structure of the polysaccharide
Change temperature
Change solvent quality
Change ionic environment
It’s what happens to amylose

7. Carrageenan (E407)
Red seaweed extract (Rhodophyceae)
iota carrageenan
lambda carrageenan
kappa carrageenan

8. 1- 4-linked-
-D-galactopyranose

9. 1-3-linked-b-D-galactopyranose
kappa
lamda
1-3-linked-b-D-galactopyranose

10. Thermoreversible gels
Kappa better gel former than iota

11. Agarose
seaweed
galactose residues
sulfated
more sulfate less well it gels

12. Importance of ions General “salt” effect Specific effects For example:
K+, Rb+, Cs+ favour gelation of both kappa and iota
Carrageenan

13. Ion

14. Gel Formation
Association of chains (junction Zones) in order to produce a permanent network
Diverse models for gel formation:
Models proposed for carrageenan

15. Atomic force microscopy
Image size 0.8 x 0.8 m

16. Alginate
Guluronic acid
Mannuronic acid

17. Gelation of alginates
High M-alginates form turbid gels low elastic modulus
High G alginates: stiff, transparent, brittle gels
Gelation depends on cation
Ba2+ > Sr2+ > Ca2+ > Mg2+

19. Pectin
a core chain of alpha (1,4)-linked D-galacturonic acid units interspersed with some L-rhamnose
R= rhamnose
U= galacturonic acid
Branched structure
Neutral sugars
alternate
About

21. galacturonic acid forming cells for cations

22. Pectin stable at low pH

23. Low ester pectin High ester pectin
Pectin with degree of esterification > 50% is referred to as high ester pectin.
High ester pectins gel in the presence of high concentrations of cosolutes (e.g. 60% sugar) and at pH values < 3.4.
Rapid set pectins have DE ~70% and slow set pectins have DE ~65%.
Gelation is believed to occur through association of the pectin chains by hydrophobic bonding.
Gels are thermally irreversible.
Low ester pectins have DE < 50%.
Low ester pectins gel in the presence of calcium ions. The reactivity increases as DE decreases.
Gelation occurs as a consequence of calcium ion crosslinking.

24. Mixed gels Often more than one polymer exists
This can enhance to reduce gel quality

25. Two component gel types
Swollen network
Interpenetrating network

26. Phase separated network
Coupled network

27. Gelation in Synergistic mixed polysaccharide gels
Locust bean gum gelling with carrageenan

28. Xanthan galactomannan gels?

29. Gel Textures Firm, Brittle Low Acyl Gellan Gum Agar k-Carrageenan
High “G” Alginate
Pectin
Gel Textures
High “M” Alginate
Gelatin
Xanthan/LBG
High Acyl Gellan Gum
Soft, Flexible

30. Useful references http://www.lsbu.ac.uk/water/
E-learning hydrocolloid program on Blackboard
Journals: Food Hydrocolloids and Carbohydrate Polymers
Series of Books: Gums and Stabilisers for the Food Industry
Book :Functional Properties of Food Macromolecules (Chapter by Morris on gelation)
Anything in the TX55-, QD4--, QP section of the library