Carrageenans
Functionality
Structuring using carrageenan
The carrageenan family is extremely diverse; it can be broadly classified into three main "ideal" types of carrageenan, split into two groups:
- Gelling carrageenans: kappa and iota
After undergoing the heat treatment required for dissolution, the macromolecules have a tendency to spontaneously associate during cooling, thus creating junction zones required for a gel.
The iota carrageenan network is formed by a series of double-helices and kinks, that form a transparent, elastic gel. This loosely-connected network can easily be destroyed by mechanical action. However, it reforms quickly once the mechanical action has stopped.
This property is called " thixotropy " and is very useful in certain applications, such as cold-filled dairy desserts.
Gelation of kappa carrageenan is particularly enhanced by the potassium ion. It induces gel formation at very low concentrations. Because of its small size when hydrated, it fits into the coil and partially neutralizes the sulfate groups. Thus, the double-helices can cluster together and form aggregates which create a strong, brittle, gel.
KAPPA (κ) 1 SULFATE FOR 2 SUGAR UNITS
IOTA (ι) 2 SULFATE FOR 2 SUGAR UNITS
- Thickening carrageenans: lambda
Mainly because of electrostatic repulsion, the chains of lambda carrageenan do not have a tendency to self-associate and can easily be separated from each other. Thus, lambda carrageenan acts simply as a thickening agent.
LAMBDA (λ) 3 SULFATE FOR 2 SUGAR UNITS
The structures described above are idealized, implying that different carrageenans are perfect chains made up of identical repetitive units. In reality, carrageenan macromolecules are not homogeneous. They are heterogeneous, either due to differing molecular structures within the chains or due to differing chains within the seaweed. For example, some carrageenans extracted from South American seaweeds are kappa and iota hybrids, also called kappa 2 or weak kappa carrageenans.
