Effect of water content, temperature and storage on the glass transition, moisture sorption characteristics and stickiness of β-casein

Moisture sorption isotherms at +4 degrees C and +22.5 degrees C were obtained for beta-casein after isolation and after 9 months of storage at -29 degrees C and +22.5 degrees C. Glass transition state diagrams (T-g vs. moisture) were determined for beta-casein after storage. The results showed that effects of storage temperature on moisture sorption isotherms were varied; however, at any a(w) differences in moisture content were small (< 0.03g H2O/g solids at high a(w)). beta-Casein stored at -29 degrees C had lower m(o) and T-g values than that of beta-casein stored at +22.5 degrees C. The glass transition temperatures for beta-casein were above room temperature, even at a(w) = 0.76. Onset of stickiness occurred above a(w) = 0.76.