The word colloid refers to a substance that has an affinity (tends to adhere) to another. Therefore, a hydrocolloid is a substance with a high affinity for water and tends to bind with it. Although proteins and starches can also be considered hydrocolloids, in this entry, we will discuss substances with a greater capacity to bind water and are usually considered food additives. We will see that there are a large number of hydrocolloids with multiple functionalities and from multiple origins. In the next entry, we will discuss their applications in baking and pastry.

Origin

There are many criteria for classifying hydrocolloids, but we will focus on the main ones, especially those that influence their functionality or homogeneity.

One of the most commonly used criteria is their origin. Thus, we have hydrocolloids obtained from leguminous seeds, such as locust bean gum or guar gum. Specifically, they are obtained from the endosperm (the germ and outer parts of the seed are separated) ground. The former is obtained from the seeds of the carob tree, a very common tree in the Mediterranean region, whose pods (carobs) have traditionally been used for animal feed. The shell of these pods, properly toasted and ground, has been used to make chocolate substitutes and has recently become popular in health food stores for its nutritional properties. Guar gum, on the other hand, is obtained from a plant similar to soy, which produces pods similar to many legumes, such as peas or beans.

We also have exudates obtained from trees or shrubs. By breaking the bark, sap is obtained, which dries and hardens on contact with the air. In this way, we obtain gum arabic, karaya gum, tragacanth gum, or ghatti gum.

There are also hydrocolloids obtained as extracts from various seaweeds. The dried seaweeds are processed using different systems to extract the soluble gums and discard the remaining components, usually rich in other types of fibres and with a high salt content. Thus, we obtain agar, carrageenans, or alginates, among other hydrocolloids.

Pectins are also obtained as an extract. This product, a common component of many fruits, can be industrially obtained from the albedo of citrus fruits or the pomace of apples, resulting from the process of obtaining juices or fermented beverages.

We can also obtain gums, such as xanthan gum or gellan gum, from the fermentation of certain microorganisms. The former is obtained by fermenting Xanthomonas campestris, and the latter by fermenting Pseudomonas elodea.

Finally, there is a wide family of hydrocolloids derived from cellulose. This fibre is one of the most abundant in nature and can be modified by different methods to obtain various functionalities. The most commonly used cellulose derivatives are methylcellulose, carboxymethyl cellulose, and hydroxypropyl methylcellulose. These products are obtained through chemical reactions to add these groups to the cellulose structure. Depending on the type of addition, the degree of substitution, and the molecular weight of the molecules, we obtain different properties.

In general, natural gums (from seeds, extracts, and exudates) may have greater heterogeneity in their functionality (thickening, emulsifying, or gelling capacity, among others) due to common variations from genetic or edaphoclimatic conditions. However, producing companies usually consider this and try to achieve the most homogeneous products possible. This type of gum is also more subject to price changes if exceptional circumstances arise, as global production is limited. For example, a few years ago, the price of guar gum increased significantly when it was used for oil extraction, and global production was insufficient to meet the demand. Some of these gums are produced in conflict-affected areas, which can also influence their annual supply. Hydrocolloids produced from microorganisms or cellulose tend to have fewer problems in this regard. In recent years, they have become cheaper due to increased supply as the number of companies producing these compounds has increased.

Properties

Another criterion for classifying hydrocolloids is their functionality or how they combine with water. Thus, we speak of thickening hydrocolloids and gelling hydrocolloids. The former bind water and reduce its mobility in the medium, increasing the viscosity of the solutions they are in. These hydrocolloids can be introduced into bread doughs or cake batters for this purpose. When using a hydrocolloid for its thickening power, it is important that the producer guarantees a certain thickening capacity and a regular water retention capacity. The technical data sheets for these products usually provide information on these characteristics. In general, hydrocolloids obtained from seeds and exudates, as well as xanthan gum, are thickeners. When mixed with aqueous solutions, they increase viscosity and create gummier textures, so they are also known as gums.

Most extracts obtained from seaweeds (agar, carrageenans, or alginates) typically have gelling properties. These products bind water, forming three-dimensional structures stabilised by different types of chemical bonds, creating a less liquid and more solid and brittle structure. Pectins, commonly used in making jams and preserves, gellan gum, and gelatine, are also gelling hydrocolloids. These hydrocolloids can be useful in making pastry products or for glazes and shines but are not as useful in doughs or batters, where the three-dimensional structure breaks down. Some of these products must be solubilised in hot water to form a gel when cooled. When using a hydrocolloid for its gelling properties, certain characteristics, such as the gelling temperature or the texture of the obtained gels, must be guaranteed.

Ionic Nature

Some hydrocolloids are non-ionic and do not carry a charge, but others are affected by certain cations in the medium, ionic strength, or pH. Thus, some hydrocolloids are more affected than others by the presence of salts. Some gelling hydrocolloids need a cation to form gels, such as calcium in the case of pectins. The presence of calcium or potassium also significantly affects the characteristics of products made with certain carrageenans. In these cases, it is important to consider their presence in the medium or the need to add these cations.

Ionic hydrocolloids, which require consideration of these factors if used, include most gelling agents (agar, alginates, carrageenans, pectins, or gellan gum), and gum arabic, tragacanth gum, or xanthan gum. Conversely, konjac gum, tara gum, guar gum, locust bean gum, and most cellulose derivatives do not have an ionic nature.

Uses

The uses of hydrocolloids in baking and pastry are vast and will be covered in a later entry. However, we can mention that they can be used in bread doughs to increase hydration and moisture retention in the final product. In cake batters, they improve moisture retention, prevent suspended substances from settling, or replace oils and fats. They can also be used in frozen doughs to reduce water migration, make glazes or shines, modify the texture of fillings, and much more. Additionally, they are essential in the production of gluten-free bread.

In each case, we must consider the functionality of each hydrocolloid, as well as legal and price aspects.

It is also important to note that some of the hydrocolloids mentioned have many variants, such as pectins or carrageenans. If they are to be used, it is necessary to analyse which type of hydrocolloid would be most suitable in each case. However, this will be discussed in other entries.

The list of permitted food additives in the European Union can be found in the official document of the Official Journal of the European Union. Hydrocolloids have E numbers ranging from 400 to 469. Among the most used in baking are locust bean gum (E 410), guar gum (E 412), xanthan gum (E 415), hydroxypropyl methylcellulose (E 464), and carboxymethyl cellulose (E 466).