Water Based Foods

Gel Formation

Carrageenan is a thermoreversible gelling agent. Gel formation is obtained only in the presence of potassium ions (kappa and iota carrageenan) or calcium ions (iota carrageenan).

When potassium ions are present, and the system is cooled below the gelling temperature, the carrageenan gels instantaneously.

As no methods of releasing potassium slowly from slightly soluble salts or complexes are known today, potassium must be present in the system or added to the system before cooling below the gelling temperature in order to avoid pregelation. However, in certain applications for instance in the making up of solid bacteriological media, gelation by diffusion of potassium ions may be used. Carrageenan may be used in instant preparations (powders to be dissolved in cold water). However, only a thickening effect is obtained, caused by swelling of the carrageenan.

When the soluble solids content increases much above 50%, the gelling temperature of carrageenan is increased to a level that limits its use. High temperature, in combination with acid-pH normally applied in products with more than 50% soluble solids, causes rapid depolymerization of carrageenan. In spite of the fact that carrageenan is a weaker gelling agent than agar, carrageenan finds extensive use as a gelling agent and stabilizing agent in the water phase of foods. This is mainly due to carrageenan's ability to produce gels with a wide variety of textures. This is understandable when it is considered that carrageenan is not just a single polymer-type but rather family of gelling and non-gelling sulfated galactans.

Combination with locust bean gum further expands the texture range available. Iota carrageenan gels exhibit the unique property of freeze/thaw stability and thixotropy.

The thixotropic nature of an iota carrageenan gel is essential when ready-to-eat water gels are filled at temperatures below the gelling temperature. Cold filling makes it possible to produce dessert gels topped with whipped cream or multilayer desserts and only an iota carrageenan gel will reform after mechanical destruction.

Stabilization

Permanent stabilization of a suspension requires the continuous liquid phase of the food to shows a yield value (a gel).

Sedimentation rate decreases with decreasing difference in specific gravity and increasing viscosity (Stokes law). Increased viscosity will slow down the sedimentation but (unless the continuous phase possesses a yield value, i.e. is a weak gel, which traps the solid particles) the sedimentation rate will never be zero.

Carrageenan is used in low concentrations to stabilize suspensions and emulsions. When used in the proper low concentrations the gel structure of the carrageenan is not detectable when the suspension is poured and consumed.

When the milk protein reactivity of carrageenan cannot be used (for instance in salad dressing and in soy protein based drinks) iota carrageenan is the preferred carrageenan as iota carrageenan produces thixotropic water gels.

Apart from the stabilizing property, carrageenan may be used to increase viscosity and add mouthfeel to a liquid food product.

Milk-Based Foods

In milk products where gelation or structural viscosity is required, carrageenan is normally preferred of function and economic reasons.

In gelled milk desserts kappa carrageenan is the most economical gelling agent to obtain a certain firmness, and is widely used in powder preparations for making flans.

In ready-to-eat flan desserts the kappa carrageenan has insufficient water binding over the required shelf life of several weeks and "weaker" kappa types, sometimes combined with iota types or LM-pectin, are used.

When ready-to-eat milk dessert must be topped with whipped cream, cold (10EC) filling must be used. Only iota carrageenan can be used as it gives a thixotropic gel - a gel which reforms after mechanical destruction.

Stabilization of cocoa particles and fat suspension in chocolate milk is obtained with as little as 0.02-0.03% kappa carrageenan. Viscosity control and foam stability of instant breakfast preparations are obtained by incorporation of lambda carrageenan. Ice cream stabilizers based on guar gum, locust bean gum and/or cellulose gum cause separation (whey off) of the ice cream mix. Low concentrations (0.01-0.02%) of kappa carrageenan forms a weak gel in the ice cream mix which prevents the separation.

Non-Food Applications

Gel formation, thickening effect, film forming ability, and diffusion rate in carrageenan gels are some of the properties which make carrageenan suited in many non-food applications.

The ability of binding water effectively and forming weak water gels which are very stable against enzymatic degradation makes carrageenan unique as a thickener in toothpaste, the gel imparting excellent stand up of the paste and excellent flavor release and risibility.

The film forming ability of carrageenan makes carrageenan an excellent conditioner in shampoo, as well as a suitable tablet coating agent.

In photographic films carrageenan may be used to increase the melting temperature of the gelatin gel.

The ability to form strong water gels in which solutes diffuse rapidly makes carrageenan a possible gelling agent for immobilization of enzymes and living cells.

Special carrageenans, which are chemically gelled without applying heat may find use as gelling agents for solid bacteriological media.

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