Impact of the CaCl2 content in the rehydration media on the microcapsule formation out of spray dried capsule precursors for the immobilization of probiotic bacteria

The aim of this work was to develop a capsule formation process at moderate temperatures with a high encapsulation yield (EY) of probiotic bacteria. Capsule precursors (CP) obtained by spray drying were rehydrated at 40 °C in aqueous solution to form water-insoluble hydrogel capsules. The CaCl₂ concentration (0–2 mm) in the rehydration solution was varied. The rehydration step was evaluated regarding matrix stability and capsule size. The results show that only low amounts of non-aggregated casein remain in the rehydration media at or above 1.3 mm CaCl₂. Additionally, under this condition the particle size distribution shows no particles with the size of non-aggregated caseins and bacteria. Both results indicate a completely, stable matrix structure. To gain a deeper understanding the EY and capsule morphology by scanning electron microscope (SEM) images were assessed. The SEM images show that the bacterial cells are fully embedded in a dense casein network structure. The determined EY was ∼85%.