Influence of Post-Treatment Temperature on the Stability and Swelling Behavior of Casein Microparticles

This study investigates the influence of exposure time and post-treatment temperature on the stability and swelling of casein microparticles prepared by depletion flocculation and film drying. Stability experiments with sodium dodecyl sulfate at 20 °C show that particles become more stable with higher post-treatment temperature and longer exposure times. The two-step decrease in decay rates in each case indicates a stable intermediate state structurally different from untreated and more strongly treated microparticles. The swelling curves of microparticles also show differences in three temperature ranges at 120 min exposure times each, which is analyzed with dynamic swelling models. At temperatures T ≤ 50 °C, the casein microparticles swell and decompose in a typical two-step process. For post-treatments in the temperature range between T = 60 and 70 °C, the swelling curves change their shape toward limited swelling to an equilibrium swelling value. The swelling curves of microparticles treated with temperatures at 80 and 90 °C show a typical overshooting, which can be analyzed with an adapted parallel swelling model and attributed to an elastic network of newly formed bonds.