W₁/O/W₂ double emulsions based on sodium alginate internal gelation: A hierarchical strategy to enhance emulsion stability and probiotic viability.

The sensitivity of probiotics to environmental stress significantly restricts their widespread application. Here, a novel W₁/O/W₂ double emulsion was constructed via sodium alginate-mediated internal gelation, and its physicochemical properties and protective efficacy for Lactobacillus plantarum were evaluated. Results showed that internal gelation significantly remodeled the emulsion microstructure, creating a compact internal assembly positively correlated with gelation intensity. Compared to the non-gelled control, the gelled emulsions exhibited superior physical, storage, and centrifugal stability, with the 1% alginate gelation intensity achieving the optimal stabilization effect. Rheological data demonstrated that the sodium alginate gel network formed in the internal aqueous phase greatly increased emulsion viscosity. It also modulated the viscoelastic behavior and built a robust physical barrier. This reinforced internal microenvironment markedly improved emulsion stability and effectively mitigated external stress, thereby significantly enhancing the viability of the entrapped probiotics. Furthermore, to further strengthen this protective effect, microcapsules fabricated via freeze-drying exhibited a uniform and dense honeycomb-like cross-linked network, characterized by excellent rehydration properties, solubility, and low moisture content. These solid microcapsules provided enhanced resistance against environmental stress, further improving the storage stability of the probiotics. In conclusion, the hierarchical strategy combining sodium alginate-mediated internal gelation and microencapsulation offered a robust engineering approach for the high-efficiency preservation of probiotics.