Salep-modified calcium-alginate beads for probiotic encapsulation

Alginate hydrogels are widely used for encapsulation; however, their inherent porosity can limit protection of probiotic cells under harsh gastrointestinal conditions. Here, glucomannan-rich salep was incorporated into Ca-alginate beads to modulate network interactions and evaluate their influence on probiotic performance. Beads containing 2% (w/v) total polymer (alginate; alginate/salep 1.5/0.5 and 1.0/1.0, w/v) were produced by extrusion into CaCl₂. Lactobacillus acidophilus LA-5 was encapsulated and the beads were characterized in terms of diameter, mechanical resistance, molecular interactions Fourier transform infrared spectroscopy (FTIR), microstructure scanning electron microscopy (SEM), and thermal behavior differential scanning calorimetry (DSC). Encapsulation efficiency remained high (93.0%-95.5%), indicating that partial replacement of alginate with salep did not compromise entrapment. Increasing salep concentration increased bead diameter (2.51-2.86 mm) but reduced hardness (9.1-7.5 g), suggesting changes in Ca²⁺-mediated junction density and network homogeneity. FTIR and DSC revealed no new covalent bonds, indicating that ionic crosslinking and hydrogen bonding dominate the stabilization mechanism, while SEM showed more heterogeneous bead surfaces upon salep incorporation. Under simulated gastric conditions (pH 2.0, 3 h), no viable cells were detected for any formulation, whereas encapsulation reduced bile-salt inhibition relative to free cells, with alginate-only beads providing the strongest protection. Although salep modified bead structure and physicomechanical properties, these changes did not improve probiotic protection under the gastrointestinal stress conditions evaluated. Overall, salep enables tunable Ca-alginate bead properties, but additional matrix engineering is required to achieve robust gastric protection.