Protective effect of milk protein based microencapsulation on bacterial survival in simulated gastric juice versus the murine gastrointestinal system

The significant decrease of live bacteria during passage of the upper gastrointestinal system is an important drawback for probiotic functional food. Microencapsulation is frequently reported to increase bacterial survival in simulated gastric juice (SGJ) but confirmatory in vivo studies are lacking. The present study aimed to characterize protective effects of milk-protein-based microcapsules in vitro as well as in mice as model consumer. Sodium caseinate (SC) and newly developed, SGJ-resistant fat SC (FSC) capsules significantly increased survival of two Lactobacillus strains in SGJ. In contrast, neither SC nor FSC microcapsules increased bacterial survival in the murine gastrointestinal system 3 or 24 h after oral uptake. This lack of protection is presumably due to rapid digestion of the microcapsules in the murine stomach. The present work demonstrates that positive results from frequently applied simple in vitro assays cannot be extrapolated to living organisms and highlights the importance of in vivo analyses.