Hydrocolloids are colloidal substances with an affinity for water. From a chemical point of view, they are macromolecular hydrophilic substances. Some of them are water soluble and form colloidal solutions others are only able to swell in water and can be dispersed by means of shear forces. Hydrocolloids pro- duce viscous solutions, pseudo-gels, or gels in water. The heterogeneous group consists of polysaccharides and proteins.
Hydrocolloids are used in technical and regulated applications to thicken and to stabilize formulations. In processed foods, they are ubiquitous – no other group of ingredients contributes more to viscosity, texture, and body like hydro- colloids do.
Hydrocolloids are not really emulsifiers because, mostly, they do not have the characteristic linkage of lipophilic and hydrophilic groups in the molecular structure. The molecules are too big and complex in size and therefore are not flexible enough to cover the interfaces being formed during homogenization of oil–water mixtures fast enough to create a long-term stable emulsion with suffi- ciently small droplet diameter. However, these thickeners can stabilize emulsions by increasing the viscosity of the water surface or by interaction with surface- active substances. Some hydrocolloids like gum Arabic or non-ionic products such as methylcellulose (MC), HPMC (hydroxypropylcellulose), or propylene glycol alginate (PGA) reduce the surface tension and exhibit limited emulsifying properties.