HYDROCOLLOIDS: PROPERTIES, TYPES, USES AND EXAMPLES - CHEMISTRY - 2024

The hydrocolloids are a large group, heterogeneous, polymeric substances mainly include polysaccharides and some protein. Its name derives from the Greek term hydro, which means water, and kolla, glue.

Among the carbohydrates or polysaccharides are hydrocolloids such as starch, agar, numerous gums, among others. There are also those of a protein nature of high commercial interest, such as soy protein, casein or caseinate, gelatin and egg white proteins, among others.

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Hydrocolloids can have different sources: natural of vegetable, animal, algae, and even some synthesized by microorganisms. They can also be semisynthetic, like cellulose derivatives.

Hydrocolloids form viscous microscopic dispersions or gels on contact with water; that is, they are hydrophilic, which is why they are also called hydrophilic colloids. They trap water within their branched, polymeric structure.

In this way, they generate different textures, viscosity and elasticity, properties that are used in the food, pharmaceutical, medical, and research industries in general.

Properties

-In their molecular structure they have a large number of hydroxyl groups (-OH. This causes them to establish hydrogen bonds with water, hence they are hydrophilic and form colloidal dispersions when in contact with it.

-Similarly, hydrocolloids can form gels due to ionic or temperature changes.

-Due to their gel-forming properties, thickeners, texturizers, among others, hydrocolloids are widely used as additives in the food industry.

-They can increase the thickness or texture of food; they serve to control the formation of ice crystals; allow varying the opacity and flavor of food.

-Hydrocolloids can be used alone and in some cases mixtures are used that offer synergistic behavior in their characteristics or properties, which increases their usefulness.

Types

Hydrocolloids can be classified considering several criteria, such as their chemical structure, their origin, their properties, among other characteristics.

According to its chemical structure

Hydrocolloids can be classified into two large groups as polysaccharides or proteins. Among the polysaccharides they can be linear, such as cellulose, alginates; or branched, such as starch and dextran, among others.

Furthermore, depending on the type of monosaccharide that makes up the polysaccharide, they may be homopolysaccharides or heteropolysaccharides.

Among the homopolysaccharides, starch is made up of long branched chains of glucose, that is, it contains the same type of monosaccharide.

Among the heteropolysaccharides or carbohydrates formed by more than one type of monosaccharides, there are hydrocolloids such as agar, gum arabic, among many others.

The group of casein, gelatin and egg white proteins, among others, are protein in nature.

According to its source or origin

According to their origin, hydrocolloids can be classified as natural -the vast majority-, as they are obtained from plants, animals, algae and microorganisms. There are some derived from natural or chemically modified derivatives, as specified below.

Vegetable in nature

From the extracts of various parts of the plants, one can mention cellulose, pectin, starch, the wide variety of gums such as arabic, tamarind gum, among others.

Of animal origin

There is gelatin, casein, egg white protein, soy protein.

Obtained from algae

Of different types of algae you have for example agar, carrageenans, alginate.

Of microbial origin

Like xanthan, dextran, curdlán, swarm, among others.

Modified or semi-synthetic

Such as methylcellulose, ethylcellulose, carboxymethylcellulose, propylene glycol alginate, modified starches, among others.

Applications

In the food industry

Hydrocolloids are used in the food industry as thickening and gelling additives. These modify the properties such as viscosity and texture of food.

Depending on the hydrocolloid used, its concentration, pH, temperature and the foods in which it is used, the shelf life is increased, the quality of the food is improved and different sensations are induced in the mouth of the diners.

As thickeners for soups, sauces, toppings and salad dressing among other foods, various types of gum are used such as arabica, guar or guaran and carob, among others. Xanthan and starch are also thickeners.

As gelling agents or gel formers, hydrocolloids such as pectin, alginate, agar, gellan and carrageenan are used mainly in jellies, jams, gelatins with little sugar and ice creams among other foods.

There are hydrocolloids, such as agar agar, which is used in cooking by vegans to avoid the use of conventional gelatin, which contains substances of animal origin in its preparation.

In pharmacy, research and clinical laboratories

Hydrocolloids such as agar are used in the preparation of different types of microbiological culture media. It constitutes the base that will give a different texture to these media, which withstand the sterilization temperatures without modifying.

As a means of carrying out different chromatography and gel filtration processes, the hydrocolloid Sephadex is used, generally used in columns. This allows the separation or purification of proteins and other biomolecules based on their different size or molecular weight.

In medicine

In dentistry under specific conditions, alginate and agar hydrocolloids are good materials for making dental impressions.

In medicine, hydrocolloids such as dextran, hydroxyethyl starch, gelatin, among others, are used in infusion fluids and volume expander solutions for the treatment of hypovolemia.

Hydrocolloids such as gums are used in the manufacture of bioadhesives for surgical dressings, dressings or coverings applied for the treatment of pressure ulcers and wounds.

Agar like cellulose cannot be digested by the digestive system of the human body, therefore it does not provide energy, but it serves as a fiber that retains water, which allows its use in medicines such as laxatives.

Examples of hydrocolloids

There are many examples of hydrocolloids that have been mentioned in the previous sections, among which the following can be expanded in more detail:

-The polysaccharide dextran. It is branched or cross-linked, and is formed by a large amount of glucose, being used in the sephadex, a gel with a spherical three-dimensional structure that has pores inside.

These spheres show variations in the crosslinking of the organic chains that make them up, obtaining different types of sephadex. The higher the crosslinking, the smaller the pore size of the sphere.

-Carrageenans, which are various types derived from galactose, include furcelarans, and are obtained from red algae of different genus and species.

-Among the variety of gums, it is worth highlighting, as an example, gum arabic, which is obtained from a resin extracted from various types of acacia.

-And finally among the derivatives of cereals are arabinoxylans , inulin, among many other examples.

References

1. AACC International Online Books. Chapter 1: Introduction to Food Hydrocolloids. Taken from: aaccipublications.aaccnet.org
2. Glyn O. Phillips, PA Williams. (2009). Handbook of Hydrocolloids. Recovered from:
3. General Overview of Food Hydrocolloids.. Taken from: application.wiley-vch.de
4. Saha, D., & Bhattacharya, S. (2010). Hydrocolloids as thickening and gelling agents in food: a critical review. Journal of Food Science and Technology, 47 (6), 587–597.
5. Jasmin Foo. (2018). How to Make Agar Agar. Snapguide. Taken from: snapguide.com
6. Wikipedia. (2018). Sephadex. Taken from: en.wikipedia.org