Structure-property relationships of alginate-protein-polysaccharide composites for encapsulation and controlled release of Lactobacillus bulgaricus LB12.

This study investigates alginate-based composites for encapsulating the probiotic strain Lactobacillus delbrueckii ssp. bulgaricus (LB12). Alginate/casein, alginate/carrageenan and alginate/casein/κ-carrageenan composites and their formulations with LB12 were prepared by ionic gelation using calcium chloride. Combined analyses (FTIR, rheological, thermal, morphological, and bacterial cell release from formulations) reveal that the microparticle network structure and physicochemical properties depend on complex interactions among constituents. FTIR spectra confirm the formation of crosslinked composites via hydrogen bonds and electrostatic interactions. Bacterial encapsulation weakened hydrogen bonds and electrostatic interactions between the composite components, thereby increasing the degree of swelling. All microparticles exhibit good mechanical and thermal stability consistent with their well-organized microstructures. Variations in storage modulus and yield strength among microparticles are consistent with morphological differences observed by microscopy, where increased formulation complexity and bacterial incorporation result in more heterogeneous, less compact particle surfaces. In vitro release studies demonstrated an initial lag phase followed by diffusion-controlled bacterial cells release from alginate/casein/LB12 formulation and swelling/relaxation of the polymer matrix for the alginate/casein/carrageenan/LB12 formulation. The findings highlight the synergistic role of alginate, casein, and carrageenan in developing effective carriers for the delivery of bacterial cells in functional food, nutraceutical and agricultural applications.