This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
Peptization is the reverse process of coagulation. It increases dispersion and solubility.
Means of bringing about peptization. Peptization may be brought about by chemical, electrical, and mechanical means or by enzymes. Freund-lich states that the hydroxyl ion is generally a very effective peptizer. Other peptizing ions used in food preparation are the citrate, acetate, and tartrate ions. Peptization brought about by adsorption has been mentioned.
Peptization of proteins. The results of Gortner, Hoffman, and Sinclair show that different salts added to wheat proteins in varying amounts to give the same pH, or in equivalent concentrations, cause peptization and solution of varying amounts of the proteins. Both cations and anions form a lyotropic series. They found the anions arranged in the following order of increasing peptization: F < SO4 < CL < tartrate < Br < I; and for the cations the following order of increasing peptization: Na < K < Li < Ba < Sr < Mg < Ca. Most of their salt solution extracts of flour had a pH of 5.0 to 6.0. This would be on the acid side of the isoelectric point of the flour proteins, and they would be positively charged. When the solubility of wheat proteins is increased, the tenderness of the resulting bread is increased.
Freundlich states that hydrophobic colloids and also solids may be peptized by suitable electrolytes, but the process does not take place spontaneously. It is necessary to divide up mechanically the liquid or solid mass very finely, in order that the charging action of the peptizing ion may be effective. In some liquids it is often sufficient to divide them by energetic stirring.
"Salting-out" of hydrophilic colloids occurs at high concentrations. But at lower concentrations electrolytes frequently bring about peptization. Freundlich states that this has been investigated particularly in some proteins or mixtures of proteins, it being found clearly in the case of globulins. Some globulins remain in solution only in the range of their isoelectric point because of the peptizing effect of electrolytes.
Both the concentration of the electrolyte and its valence affect the extent of peptization. In general, the peptizing action is increased with increasing valence. For example, there is little peptization with the chlorine ion, the sulfate ion peptizes in higher concentrations, and the citrate ion brings about peptization with low concentrations.