The Rheological Properties of Carrageenan gel

The Rheological Properties of Carrageenan gel

On account of its properties, carrageenan gel is often used in food industry as the thickening, gelatinizing, suspending, emulsifying and stabilizing agents. Besides, it is also widely used in medicine and fine chemical industries. However, the production and application of carrageenan have much to do with its rheological properties, so it is of great significance to production to have an accurate mastery of its rheological properties and the change rule under various conditions.

 

1. Viscosity

Carrageenan gel can form high-viscosity solution. For example, the average viscosity of 2% aqueous solution (free of metal ions) is 500~1000 cps. Many factors can influence the solution viscosity, such as molecular weight, concentration, temperature, type of carrageenan, and the cation in the solution.

Properties of Carrageenan-carrageenan gel

1.1 Influence of its molecular weight on the solution viscosity

The viscosity of carrageenan gel increases remarkably with the increase of its molecular weight. The molecular weight distribution of food-grade carrageenan is about 200,000 daltons. Carrageenan with molecular weight under 100, 000 daltons has very low viscosity and has no commercial value at present.

 

1.2 Influence of its concentration on the solution viscosity

The solution viscosity of carrageenan gel rises exponentially with the increase of its concentration. This is the typical feature of linear charged molecules and is also caused by the strong repelling of electrons on the anionic polysaccharide chains under a neutral pH condition when the interaction of macromolecules enhances with the rise of its concentration.

 

1.3 Influence of its temperature on the solution viscosity

With the increase of temperature, the solution viscosity of carrageenan gel , however, decreases exponentially. In the stable state, the viscosity and temperature seem to be reversible. However, the rate of viscosity-temperature curve is different during temperature-rise and temperature-fall periods. The rate of curve is low during the temperature-rise process. However, the viscosity will sharp increase when the temperature cools down to 30℃. In the temperature-fall period, the viscosity will suddenly increase when the kappa-carrageenan and ι-carrageenan reach their gel points while the λ-carrageenan won’t do so.

 

1.4 Influence of constant temperature heating time on the solution viscosity

At the temperature of 75℃, the solution viscosity of carrageenan gel decreases with the longer period of constant temperature, because the dissociation of its macromolecules will occur with the heat of solution, the molecular entanglement reduces, and thus the viscosity decreases. When the temperature reaches 100℃, the viscosity will also decrease over time but sometimes slowly and sometimes quickly. It works like this. At the very beginning, the molecular entanglement is broken by the heat, so the viscosity decreases. Afterwards, it moves to a smooth stage. Later, a few unstable macromolecules begin degradation and the viscosity decreases again.

 

1.5 Influence of rotation rate on the solution viscosity

With the increase of rotation rate, the solution viscosity of carrageenan gel will slowly decrease and the carrageenan solution shows pseudoplastic. The viscosity is in relation to the shear force during the testing period and the solution possesses the shear thinning property at that time.

 

1.6 Influence of stirring time on the solution viscosity

With the longer stirring time, the viscosity of carrageenan gel solution will first rise slowly and then decrease 80 minutes later, because the stirring process helps to break up molecular group and the broken up molecules will automatically gather to entangle. Consequently, the molecular entanglement will increase with the longer stirring time and thus its viscosity rises. When the molecules aggregate, to some extent, to form small flocculent particles and are scattered, the viscosity will decrease instead. If the stirring time is over 80 minutes, the viscosity will decrease and its resistance to mechanical damage will become poorer.

 

1.7 Influence of pH value on the solution viscosity

The viscosity of carrageenan gel solution will rise with the increase of pH value, but becomes stable when pH value is close to neutral and later on decrease instead. When its acidity becomes strong, H+will increase and this, on one hand, helps to the dissociation of carrageenan molecules and the neutralization of its electric property. On the other hand, it weakened the electrostatic attraction of semi-esterified sulfate ions. When the basicity becomes strong, OH- and electronegative carrageenan mutually repel, so the molecular entanglement will decrease. Consequently, under the conditions of strong acid or strong basicity, the viscosity will decrease.

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On January 31st, 2013, posted in: carrageenan, Products and Techniques by Tags:

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