Abstract: The effect of ultra-pasteurization (121 ℃/5 s) on the microstructure and aggregation properties of casein in milk was investigated in comparison with non-thermally treated milk and two commonly used pasteurization treatments (65 ℃/30 min, and 72 ℃/15 s). The results showed that the particle size of casein increased significantly after ultra-pasteurization. Under transmission electron microscopy and scanning electron microscopy it was observed that ultra-pasteurization could destroy the casein micelle structure and result in large-scale cross-linking and coagulation, but the coagulation could result in a more uniform state of casein micelles. Differential scanning calorimetry (DSC) analysis showed that the samples treated with ultra-pasteurization had a slightly higher denaturation temperature than the casein micelles without heat treatment. The thermal stability of casein was increased after the second pasteurization treatment when compared with the other treatments, and the denaturation temperature was 99 ℃.

Key words: ultra-pasteurization, pasteurization, casein, microstructure, aggregation properties