Water sorption caseinate

In milk powders, the caseins are the principal water sorbants at low and intermediate values of aw. The water sorption characteristics of the caseins are influenced by their micellar state, their tendency towards self-association, their degree of phosphorylation and their ability to swell. Sorption isotherms for casein micelles and sodium caseinate (Figure 7.14) are generally sigmoidal. However, isotherms of sodium caseinate show a marked increase at aw between 0.75 and 0.95. This has been attributed to the... 

FIGURE 8.3 Water vapor pressure or water sorption isotherms of foods. Given are water content versus water activity (aw). (a) skim milk (powder), (b) Various foods meat (1), apple (2), boiled sweet (3), skim milk (4), and peanuts (5). (c) Caseinate systems (water content expressed asg perg dry protein) pure caseinate (1), curd or renneted milk (2), and cheese (3). 

Hysteresis phenomena in the water sorption by high polymers [125] and by other proteins such as wool fiber [125] and casein [126] have also been described. Smith [125] suggests that hysteresis is a result of differences in the ratio of bound to free water in the substrate, with a larger amount of bound water present on desorption than on absorption. 

Fabra, M.J., Talens, P., Chiralt, A. Water sorption isotherms and phase transitions of sodium caseinate—lipid films as affected by lipid interactions. Food Hydrocolloids 24, 384-391 (2010)... 

Kristo, E. Biliaderis, C. G. (2006). Water sorption and thermo-mechanical properties of water/sorbitol-plasticized composite biopolymer films caseinate-pullulan bilayers and blends. Food Hydrocolloids, 20(7), 1057-1071. 

---