Encapsulation of Bifidobacterium adolescentis 15703T in gelatin-maltodextrin microspheres to improve survival during gastrointestinal transition

Bifdobacterium adolescentis cells were encapsulated in genipin (GP) crosslinked gelatin (G) and maltodextrin (MD) hydrogels using an emulsification/phase separation technique. Two kinds of microspheres were obtained: phase separated GMD capsules made from 10 or 16% w/v gelatin with 3% w/v MD and homogeneous G beads consisting of 10 or 16% w/v gelatin that served as controls. Confocal Laser Scanning Microscopy and cryo Scanning Electron Microscopy images of the phase separated structured beads revealed two distinct phase morphologies, where core-shell and multi-core structures were generated by phase separation of 10/3 and 16/3 GMD mixtures respectively. Microscopy studies showed that bacterial cells were associated with maltodextrin inclusions and distributed mostly at the GMD interface.; The microsphere parameters: size, bacterial load and stability in simulated gastric conditions, were investigated and optimized. Small and large G and GMD microspheres with average diameters of 37 mum (range of 20-50 mum) and 70 mum (range of 60-90 mum) were produced by modulating the factors affecting size and size distribution. It was found that increasing the homogenization speed from 1300 to 1600 rpm and surfactant Span 85 concentration from 0.0 to 1.5% yielded microspheres with a smaller mean size. Using Principal Component Analysis, distinct size separation between the microspheres produced without and with 1.0% surfactant as well as a trend of increasing size with increasing total polymer concentration was observed. Genipin crosslinking significantly reduced the microsphere size at concentrations above 15 mM. The microsphere bacterial load evaluated after enzymatic degradation of the GP-crosslinked gelatin network was between 9.0 and 9.8 log cfu/g. A stability test in simulated gastric juice (SGJ) showed that increasing genipin concentration to 24 mM dramatically improved the microsphere structural resistance against enzymatic and low pH degradation.; In vitro challenge experiments revealed that both homogeneous and phase-separated microspheres exerted a protective effect on encapsulated B. adolescentis cells. However, the viability of B. adolescentis in SGJ (pH 2.0) and during sequential incubation in SGJ and simulated intestinal juice (SIJ) with bile was significantly (p < 0.05) enhanced by encapsulation in composite GMD microspheres as compared to homogeneous microspheres and free cells. Investigation of the effect of MD on the survival of B. adolescentis in SGJ (pH 2.0) suggested that MD helped to protect the cells during exposure to low pH. Inhibition of proton translocating enzymes by addition of N,N-dicyclohexylcarbodiimide decreased the protective ability of MD at pH 2.0.; The results obtained in this study indicate that the novel microencapsulation formulation exploiting GP crosslinked GMD biomaterials may be effectively used to protect bifidobacteria from adverse GI conditions.