Simulation Code

Casein microparticles produced from casein micelles by depletion flocculation and filmdrying under pH-neutral ambient conditions are spherically round and have a spongelikemicrostructure. Heat treatment at T = 50 °C and 80 °C creates new physical orcovalent bonds between the caseins, which influence the expansion and stabilitybehaviour under gastric conditions. For both thermally stabilised and untreatedmicroparticles, we observe similar complex changes in overall size in opticallytransparent swelling cells after replacement of the medium by simulated gastric fluid.Control experiments show that pepsin becomes active later in the process and causesa final exponential decrease in particle area to a stable final value through proteolyticdegradation. The previous more or less pronounced expansion, the subsequentshrinking process and the renewed swelling can be attributed to structural changes inthe casein phase due to the acidification of the particles. Accompanying the changes inoverall size, we resolved microstructural details using confocal fluorescencemicroscopy. Before treatment with simulated gastric fluid, particles heat-treated at 80°C show a broadened tubular microstructure at the surface and a depletion of thecasein phase in the centre, in contrast to the other preparations. After 2 hours ofgastric acid treatment, the tubular microstructure on the surface of all particlepreparations is retained despite drastic shrinkage. Due to accelerated enzymaticdegradation, we now observe a depletion of casein in the interior of the untreatedparticles, whereas a homogeneously distributed casein phase is observed in thethermally stabilised samples.