BIOMATERIAL
[Gelling Polysaccharide]
Nur Istianah, ST.,MT.,M.Eng
Gelation of proteins
• 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.
X X X
Polysaccharides X
• 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.
Gels
X
X
X
X
Gel structures
Aggregates of spherical particles Framework of Rod-like particles Aggregates of spherical particles Framework of Rod-like particles
Physical gel with crystalline junctions Chemical gel -covalent junctions
Structure of the polysaccharide
•
Change temperature
•
Change solvent quality
•
Change ionic environment
It’s what happens to amylose
Carrageenan (E407)
Red seaweed extract (Rhodophyceae)
iota carrageenan lambda carrageenan kappa carrageenan
Thermoreversible gels
Kappa better gel former than iota
Importance of ions
• General “salt” effect
• Specific effects
For example:
K+, Rb+, Cs+ favour gelation of both kappa and iota Carrageenan
Carrageenan
Ion
Gel Formation
Diverse models for gel formation:
10 Models proposed for carrageenan
Association of chains (junction Zones) in order to produce a permanent network
Alginate
Mannuronic acid Guluronic acid
Gelation of alginates
• High M-alginates form turbid gels low elastic modulus
• High G alginates: stiff, transparent, brittle gels
• Gelation depends on cation
• Gelation depends on cation
• Ba 2+ > Sr 2+ > Ca 2+ > Mg 2+
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 40-100
• 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
High ester pectin Low ester pectin
• Low ester pectins have DE < 50%.
• Low ester pectins gel in the presence of calcium ions. The reactivity increases as DE
16
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.
reactivity increases as DE decreases.
• Gelation occurs as a consequence of calcium ion crosslinking.
Xanthan galactomannan gels
?
Firm, Brittle
Pectin High “G” Alginate
κκκκ -Carrageenan Agar Low Acyl Gellan Gum
Soft, Flexible
18Xanthan/LBG
Gelatin
High “M” Alginate
High Acyl Gellan Gum
THANK YOU
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--, QP7-- section of the library
