Hydrocolloids versus proteins, surfactants and
(nano)particles
Hydrocolloid emulsifiers have certain general functional char- acteristics resembling those of all the other main categories of food emulsifying agents: proteins, surfactants and solid particles. Nevertheless, being hydrophilic polymer molecules, hydrocolloids also differ in certain respects from these other species. As an aid to understanding the structure/function relationship of hydrocolloids, we here compare these ingredients in more detail.
When the emulsifier concentration is low, and electrostatic interactions are largely suppressed, the emulsification behaviour is qualitatively similar for all the various types of emulsifiers. That is, the initially formed droplets are only partially covered with poly- mer/protein/surfactant/particles, and the droplets coalesce with others until their surfaces become protected by a dense layer of molecules/particles. Additionally, bridging flocculation may occur due to sharing of droplet surfaces by adsorbed particles or macro- molecules (see Fig. 1). When the emulsifier concentration is high, though, the mean droplet size depends on the emulsifier type exclusively through the interfacial tension. The relevant property here is the equilibrium (static) tension for fast adsorbing surfac- tants, but it is the dynamic surface tension for the more slowly adsorbing macromolecular emulsifiers, i.e., proteins and, especially, hydrocolloids. For particle emulsifiers acting alone, the relevant property is the interfacial tension of the bare oil–water interface