Construction of multilayer alginate hydrogel beads for oral delivery of probiotics cells

Multilayer alginate hydrogel beads (MAHBs), which were prepared by emulsion method, had been fabricated via the ionic crosslinking between calcium ion (Ca²⁺) and carboxylic group of alginate and utilized as encapsulating material for oral delivery of a model probiotic bacteria Bifidobacterium breve. Optical and fluorescence microscopy obviously showed the microorganism cells were encapsulated in the core beads. The viability of B. breve cells encapsulated in MAHBs was significantly enhanced compared with ordinary free cultured ones, the top CFU per mL were (3.70±0.20)×10⁷ and (2.61±0.22)×10⁷ respectively. Meanwhile, B. breve cells encapsulated in MAHBs could still keep viability even after 12h' culture in the broth with pH value similar to gastric juice, while the free cultured cells had no activity in such culture condition. To test applicability of MAHBs for the delivery of microorganisms, a Gram-positive strain, Staphylococcus aureus, as well as a Gram-negative strain, Escherichia coli, were also employed and encapsulated in MAHBs. Similar to B. breve cells, the viability of encapsulated S. aureus cells and E. coli cells in extreme pH value environment were significantly promoted. In addition, a high α-amylase yielding efficiency Bacillus subtilis strain was found and encapsulated in MAHBs. Compared with control groups, MAHBs encapsulated B. subtilis cells produced more α-amylase after 240h' culture, while the release of this enzyme was sustained rather than the burst release like free cultured group, which means this system would not reduce metabolite yield while having long term sustained-release effect. In summary, MAHBs are favorable biological carrier, which has the potential of being applied to oral delivery of probiotics.