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How to use Alginates

Making a homogeneous solution is the most important procedure to obtain the maximum performance of “ALGIN”, which is a general term for the group of alginic acid, alginate salts and alginate derivatives.
The negatively charged carboxyl groups in alginates cause the straight alginate chains to repel each other and this results in a stable aqueous solution. This aqueous solution has smooth flow properties with Newtonian behavior.
ALGIN is a water-soluble polysaccharide and gives a viscous colloidal solution.
Sodium alginate has a strong affinity with water and care is required to achieve a homogeneous aqueous solution.
It is most important to first prepare a uniform aqueous solution of ALGIN before it is utilized as a thickening agent, gelling agent, etc. Poor dispersion in water will occur if sodium alginate is added too rapidly, producing pasty, flour-like lumps wetted only on the outside.
The solubility of ALGIN in water and solvents is illustrated below.

Solubility of Alginates

  • Salts of alginic acid with monovalent cations (Na-salt, K-salt, NH4-salt) as well as Propylene Glycol Alginate are all soluble in cold & hot water, and generate viscous aqueous solutions (Table 1).
  • Alginic acid and calcium alginate are water-insoluble.
  • All the alginate salts are insoluble to fats & oils and organic solvents.

Table 1: Solubility of ALGIN in various types of solvent

Type of Alginate Solubility
Cold & Hot water Fats & Oils Organic solvents
Alginic Acid Insoluble Insoluble Insoluble
Sodium Alginate Soluble Insoluble Insoluble
Potassium Alginate Soluble Insoluble Insoluble
Calcium Alginate Insoluble Insoluble Insoluble
Ammonium Alginate Soluble Insoluble Insoluble
Propylene Glycol Alginate Soluble Insoluble Insoluble
  • Solubility of ALGIN can alter with the properties of the solution (pH, concentration of cation, etc.)
  • Care is required when making a solution of low pH or a solution that contains polyvalent cations, because ALGIN has a limited solubility in these systems.

Table 2: Solubility of ALGIN in various types of solution

  Solubility
In an acidic system In an alkaline system In a solution with polyvalent cations
Fruit juice, Sake, Salad dressing, etc. Lye water, etc. Hard water, Milk, etc.
Alginic Acid Insoluble Soluble Insoluble
Sodium Alginate Insoluble Soluble[1] Insoluble
Potassium Alginate Insoluble Soluble[1] Insoluble
Calcium Alginate Insoluble Insoluble[2] Insoluble
Ammonium Alginate Insoluble Soluble[1] Insoluble
Propylene Glycol Alginate Soluble Soluble[3] Soluble

Notice

  • 1: It shows that the viscosity of ALGIN solution decreases in highly alkaline systems.
  • 2: In Table 2 above, it is observed that ALGIN dissolves in the certain alkaline systems.
  • 3: In neutral and alkaline systems, Alginate Ester is decomposed and generates alginate salt.

Dispersion of alginate to produce a homogeneous alginate solution

  • Alginate product as a dried powder.
    We have a variety of products from granules to fine mesh for various applications.
  • To dissolve alginate in a short time, it is important to disperse alginate into the water uniformly. Alginate powder dispersed in water gradually swells and dissolves.
  • Alginate which is dispersed uniformly has a large surface area and can be dissolved in a short time. Meanwhile, it takes longer for the lumps to swell and dissolve.
Good Good
Not Good Not Good
“How to disperse homogeneously”
  • (1) Using a high speed stirrer
    Add alginate powder to the water gradually with rapid stirring.
  • (2) Premix with a hydrophilic powder
    Before dispersing into water, make a uniform mixture of sodium alginate powder with a hydrophilic powder, such as sugar. Then, add the mixture into water as in 1.
  • (3) Premix with a hydrophilic liquid
    Before dispersing, make a wet mixture of sodium alginate powder with a hydrophilic liquid, such as alcohol and glycerin. Then add the mixture into water with stirring.

Dispersion and dissolution using a high speed stirrer

“By rapid stirring”
  • Add sodium alginate gradually into the water while stirring using a high speed propeller-type stirrer.
  • Keep stirring the solution until all the alginate material is dissolved.

Notice

  • * This is the standard method to disperse and dissolve alginate into water in a short time.
  • * For this method, a high speed stirrer is required which has enough power to stir the water inside the tank.
  • * When alginate is dissolved, the solution becomes viscous. Thus, a stirrer which can stir viscous liquids is required.
  • * If any powder adheres to the blades, wall of the tank, etc., stop stirring and check.
“Poor dispersion with lumps”

Dispersion and dissolution by premixing

“Premix with a hydrophilic powder”
  • Before adding to water, premix with a hydrophilic powder such as sugar and salt. It reduces the time to dissolve and avoids lumps with a slow speed stirrer.
  • Once dispersed uniformly, a homogeneous solution is easily obtained.
  • To disperse effectively, the quantity of hydrophilic powder should be 6 times the alginate powder.
“Example with sugar”
  • 1. Premix sugar with alginate thoroughly.
  • 2. Premixed alginate can be easily dispersed in water at slow stirring speed.
  1. Premixed alginate can be easily dispersed with slow stirring speed, lumps are not generated.

  2. Lumps are not generated after the alginate powder starts to swell as the alginate and sugar are well dispersed.

  3. Leave or maintain slow stirring, until a smooth alginate solution is obtained.

Notice

  • * Premixing with a high viscous powder can improve dispersibility, but occasionally, depending on the alginate type, it may not dissolve thoroughly.
“With alcohol”
  • Alginate is not soluble in alcohol.
  • Add a small quantity of alcohol (e.g. ethanol) to the alginate powder and make a slurry. Add water to this slurry immediately, this causes the alginate to disperse without lumps.
  • Once dispersed, it is possible to make a homogeneous solution even at slow stirring speeds.
“Example with alcohol”
  1. 1. Add alcohol to the alginate powder and make a slurry.
  2. 2. Keep stirring the slurry and add water at once.
  1. Add alcohol to the alginate powder and make a slurry. Increasing the quantity of alcohol makes the alginate easier to disperse.

  2. Add water to the slurry, with stirring, to avoid precipitation of the alginate powder.

  3. Leave or maintain slow stirring, until a smooth alginate solution obtained.

Notice

  • * Unlike the example with sugar, add water to the alginate/alcohol slurry instead of adding alginate directly into water.

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