How Does Sodium Alginate Thicken?

Sodium alginate is mainly used in the food industry as a gelling agent and thickener. Of all its applications, the gelling effect is employed the most. It forms a sodium alginate gel via a cross-linkage with calcium ions and has a very short gelation time. However, the sodium alginate gelation mechanism and the factors affecting the gelation are still much more complicated. This article focuses on and analyses the finer processes of how sodium alginate thickens and its characteristics.

Sodium Alginate Gel Formation

As the concentration of the divalent cations increases, the sodium alginate forms transparent, thermos-irreversible gels at normal temperature conditions. Some of the cations which cause gelation are Ca2+, Pb2+, and Cu2+. Although Pb2+ and Cu2+ have considerably higher interactions with sodium alginate molecules, the usage of such beads is restricted due to the toxicity of these cations. Hence, calcium sources like Ca2+ are preferred for sodium alginate for food due to their safety.

Let’s discuss now the sodium alginate gelation mechanism. The process of gelation of sodium alginate is dissimilar to other types of food thickeners, particularly agar and carrageenan. For instance, agar needs to be heated and cooled to form a gel but sodium alginate gelling agent will gel immediately at room temperature when it meets a Calcium source and is heat reversible. This is a big plus in all sodium alginate uses especially in the food industry where gelling is required. Moreover, this property makes sodium alginate appropriate in instances where heat stability is critical, for example in processed foods, and cooked dishes as well as in spherification for culinary usage in modular gastronomy.

The other notable characteristic that deserves mention about sodium alginate gel is that it is transparent. Transparent gels have several applications in foods in which the latter’s transparency is of consideration. As a result, sodium alginate has become a critical tool in most contemporary culinary practices and processed food manufacturing.

How to Make Sodium Alginate Gel?

In contrast to other gel alginate techniques, sodium alginate gel does not undergo solidification by heat. This specificity arises from electrostatic attraction between calcium ions and dissolving sodium alginate polymers. On the other hand, agar gels require heat for them to dissolve at 85°C and require unique conditions to solidify. This gel stabilizes at higher temperatures in sodium alginate applications, which makes the food additive sodium alginate suitable for use on foods that go through heat treatment.

To make sodium alginate gel one can dissolve powdered sodium alginate in water, add a solution of calcium salt, and allow it react. The calcium ions bind with the sodium alginate chains through a cross-linking mechanism that leads to the formation of a gel. The process can be regulated by changing the concentration of sodium alginate and calcium salt; this determines the strength, elasticity, and water-absorbing capacity of the gel.

A very prominent application of sodium alginate gelling agent is in the preparation of artificial caviar or imitation pearls. In this technique, a flavored sodium alginate solution is dropped into a calcium chloride solution forming small caviar-like spheres of gel. This method is displayed good example of the use of sodium alginate in other cooking techniques.

Main Influencing Factors of Sodium Alginate Gel Formation

Several factors control the formation and properties of sodium alginate gel. These include:

Type of Sodium Alginate

For gel strength, both the viscosity of sodium alginate and the concentration of guluronic acid (G unit) are very important. High-G types produce high-modulus, stiff, and brittle gels with high thermal stability while high M types produce elastic gels which have low modulus but low mechanical strength.

Depending on the regulation of the extraction process, manufacturers can control the degree of polymerization required to produce the powdered sodium alginate of the desired viscosity. Polymerization of the monomers gives gels and the strength of gels increases to the extent of polymerization because of strong covalent bonds between long and larger columns of molecules. Further, the choice of the type of sodium alginate also depends on the specific gel properties for a given application. Thus high-G sodium alginate is used in strong gel products while high-M sodium alginate is used in elastic gel products.

Type of Calcium Sources

Calcium sources are important in the preparation of the gel for it to have the best qualities. Among soluble calcium salts, calcium chloride, and calcium lactate is effective when the pH level is neutral. However, the calcium chloride delays this process significantly and is incapable of providing uniformly sized gels. In some cases, it is better to use slow soluble calcium salts such as calcium sulfate, because while dissolving from the liquid gel, dissolving sodium alginate requires more time, through which the gel can acquire a better uniformity.

Another influential factor is the calcium ion concentration or direct proportion with the calcium ion concentration also having a direct proportion. An increase in the concentration of liquid sodium alginate enhances the water absorption; elasticity, and gel strength because denser networks can be produced upon gelation. However, it was found that when calcium sources are added, it may result in over-gelation and hence a rigid structure. On the other hand, if the concentration of calcium ions is low, the gels are formed which do not have a strong structure. So, the regulation of calcium ion concentration is critical to the achievement of the right texture of the gel.

Calcium Ion Chelating Agents

Chelating agents slow down the gelation rate by holding excess Ca2+ ions; hence, more time is given to dissolving sodium alginate. This enhances the evenness and quality of the gel being developed to be used in the formation of the composite. However, this has the disadvantages of high calcium ion wastage and low efficiency due to the aggregation of calcium additives.

A slower gel formation rate is usually controlled by chelating agents like sodium hexametaphosphate in the food products. It also assists in reducing the gelation during the preparation process to achieve control over the texture and quality of the formed gel. Although it makes the process more complicated, the use of chelating agents is crucial in industrial processes where tight control of the process is required.

Temperature

Temperature impacts the sodium alginate gel uses by implications on the dissolution rates of calcium salts and sodium alginate. Vinegar gels at a faster pace at higher temperatures, since molecular activity is directly related to temperature. But, heat at a high degree leads to the prevention of gel formation. A cooling gelation method is one with the solution being made in hot water and then cooled to induce gelation. After gelation, sodium alginate gel is thermostable and exhibits the heat-renewable nature of the gel system.

In some applications, temperature control is very important, to get very strong gels and very clear as well. For example, during beverage clarification operations, soluble sodium alginate is employed as a coating of impurities; these are the particles that after being encapsulated using edible sodium alginate can be filtered out. The applied method of enzymatic reaction prescribes a specific temperature regime based upon which the desired gel formation will occur without detriment to taste or texture.

pH Value

pH level affects the solubility of calcium salts and in turn the gelation process. Reducing acidity by adding acids dissolves the insoluble calcium salts which release the Ca2+ more easily soluble forms. Sodium alginate gel obtained in this manner has better gel formation and better properties than edible sodium alginate gels.

Proper gel strength and consistency depend highly on the range of the pH level. High temperatures are capable of accelerating the gelation process while low temperatures slow down the gelation process. Excessive gelation may be caused by a high concentration of acid, while gelation may be hampered by a high concentration of alkali. In the industrial production of gel foods, pH control is used to ensure the specific pH level is maintained throughout the production process to achieve uniformity of the gel.

Sodium Alginate Applications and Benefits

There are different sodium alginate applications in almost all industrial sectors. As mainly applied as a stabilizing and food thickener, their application enhances texture in a wide range of food items. Also, because it can create gels that can withstand high temperatures, the product is suitable for high-temperature processes in the food sector.

Apart from the widely used functions in food industries, sodium alginate has applications in pharmaceuticals, cosmetics, and textile printing. It is used in the formulation of drugs to act as a stabilizer as well as a controlled release agent in the formulation. It is used in cosmetic formulations to thicken creams and lotions, offers product easy spreadability, and enhances product stability.

Cost and Availability

The price of sodium alginate depends upon the type, viscosity, and purity of the substance that is used in the synthesis. High-G sodium alginate is generally more expensive than high-P sodium alginate as used in the food industry because of its higher gelation properties. Nonetheless, as a result of these factors, it possesses certain advantages over the other sources of sodium alginate that make it reasonable for some of the more diverse uses of sodium alginate in the long run.

Over the recent past, extraction and processing technology advanced, and this led to cheaper sodium alginate that is used in commercial and industrial production. Suppliers can be divided into broader and targeted, and the majority of them have a very extensive portfolio to meet all producers’ needs, enabling users to choose the most suitable variety unquestionably.

Conclusion

Knowing the mechanism of how sodium alginate thickens helps different forms of industries to fully utilize its possible uses. In addition to food thickener, sodium alginate gelling agent, as well as a stabilizer, this compound has proven very useful in improving the quality of the products as well.

Since the future is inclined to natural and safer food preservatives and additives, sodium alginate for food still stands as better than others in thickening in gelling properties. Further studies and developments have been made, so it is possible to reveal new opportunities, and other new ideas in foods, medicines, and others.

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