Stabilizing interactions of casein microparticles after a thermal post-treatment

Casein microparticles from milk are important carrier materials for bioactive substances with stability and swelling properties that can be influenced by heat treatment. Microparticles produced by depletion flocculation and film drying remain stable in acidic media but swell and disintegrate under slightly alkaline conditions. Heat treatment after formation can stabilize the microparticles via a disulfide bridge network and newly formed hydrophobic contacts. Temperatures >60 °C are required so that denatured whey protein initiate formation of disulfide bridges via thiol exchange reactions. The particles then swell in a two-step process and exhibit an overshooting effect. If formation of disulphide bridges is prevented during heat treatment by adding N-methylmaleimide, overshooting swelling disappears and microparticles continue to expand instead. The analysis with parallel system dynamics models is based on the swelling of uncross-linked caseins, which is limited by the expansion capacity of cross-linked caseins.