Protein Gelation

Gels consist of 3D networks (with junctions that can be polimer or polisacharides) of a biopolymer in which water is trapped and retained (Gelatine, pudin, boiled egg). These biopolimers are polysaccharides or proteins, or combinations of both. The junctions are neded in order to be able to build the network.

The properties of the gel are largely dominated by two types of interaction forces: protein protein interactions and water-protein interactions. In fact these two proteins are to some extend opposing each other a bit, so they should be in good balance in order to ensure a good gel network. A good gel network consists of a gel wich over the time retains its water. So the water does not leak out of the gel network, this process is known as syneresis. Typically this process is not desirable.

As mentioned, protein-protein and water-protein interactions should be balanced. It p-p interactions dominate, then proteins will form clusters, which grow bigger and finally will become insoluble in the aqueous solutions. The result is an agglomerations and coagulation of proteins, resulting in bigger protein particles which precipitate from the solution. Sometimes these coagulated proteins may still contain some water, but in general considerably lower amounts compared to those present in the original protein-water mixture. A typical example would be a casein curd which is obtained during cheese making. The curd obtained in this case though can still be considered as a gel, since sufficient protein-water water interactions are still present too. If protein water interactions are dominations then the proteins will not show a tendency to interact with each other. As a result the 3D network needed to form the 3D structure of gel will not be formed, or only to a limited extend. Possible viscosity of the protein solution can be increased because some water can be retained  and temporary a 3D network between the protein can be formed, which is however not stable and will be disturbed by the Brownian motion of all molecules present in the aqueous protein. 

These aspects are illustrated in the figures:

1: Represents  individual protein particles which are sometimes interacting with each other, but mainly interact with water, thus a 3D network is not created.

2And 3: The protein interactions increase and as it can be observed protein strings are being created which are interactions at some points thus creating juctions, it is a 3D structure so the water is entrapped into the structure.

4 the proteins interact so strongly that in fact the water is being expelled out of the protein-water system, giving rise to protein clumps which become unsoluble in the aqueous system and thus precipitate.