Studies in Physico-Chemical Properties of Caseins Part I : pH-Titration Curves

The pH-titration curves of caseins isolated from milk by different methods, using NaOH, Ba(OH)₂, NH₄OH and HCl as the titrants, have been obtained. The caseins isolated by the rennet and ultracentrifuge methods, being the original calciumcaseinate-phosphate complexes, have higher initial pH values and con­sume less alkalies and more acids than those isolated at their isoelectric points by the addition of acids (acid caseins). The amount of ammonia taken up by casein is more than that of other alkalies, probably due to hydrogen bonding with some of the functional groups. The acid caseins behave as dibasic acids like the con­stituent amino acids. The heats of ionisation at different pH values have been determined by using van't Hoff equation and necessary informat ion regarding pH range in which various acidic groups ionise has been obtained. This permits the determination of the various ionisable groups in caseins.