Code for Simulation

Casein microparticles produced from casein micelles by depletion flocculation and film drying under pH-neutral ambient conditions are spherically round and have a spongelike microstructure. Heat treatment at T = 50 °C and 80 °C creates new physical or covalent bonds between the caseins, which influence the expansion and stability behaviour under gastric conditions. For both thermally stabilised and untreated microparticles, we observe similar complex changes in overall size in optically transparent swelling cells after replacement of the medium by simulated gastric fluid. Control experiments show that pepsin becomes active later in the process and causes a final exponential decrease in particle area to a stable final value through proteolytic degradation. The previous more or less pronounced expansion, the subsequent shrinking process and the renewed swelling can be attributed to structural changes in the casein phase due to the acidification of the particles. Accompanying the changes in overall size, we resolved microstructural details using confocal fluorescence microscopy. Before treatment with simulated gastric fluid, particles heat-treated at 80 °C show a broadened tubular microstructure at the surface and a depletion of the casein phase in the centre, in contrast to the other preparations. After 2 hours of gastric acid treatment, the tubular microstructure on the surface of all particle preparations is retained despite drastic shrinkage. Due to accelerated enzymatic degradation, we now observe a depletion of casein in the interior of the untreated particles, whereas a homogeneously distributed casein phase is observed in the thermally stabilised samples.