Studies in Physico-Chemical Properties of Caseins : Part. II. Sorption of Water Vapour by Caseins

Sorption isotherms of water at 30° on different samples of casein isolated by different methods from cows' milk and buffalos' milk have been studied and the data interpreted in the light of BET and Harkins-Jura equations. The values of specific surface area obtained by both the methods are in fairly good agreement keeping in view the differences in the postulates involved. The values of V at 0·18 r.v.p. is close to Vm of BET equation and this enables calculation of surface area of caseins from a single point on the isotherm. It appears that sorption of water proceeds initially at the sites provided by ionic groups and then by non-ionic polar groups of the side-chains and that one molecule of water is attached per polar group. Thereafter begins further condensation of water molecules not only on the above mentioned sites, but also inside the polypeptide skeleton forming casein solution. This causes weakening of the peptide bonds leading to denaturation and putrefaction of the casein