Hollow-core wood hemicellulose-based microcapsules entrap probiotics within protective walls

Microencapsulation of bioactive compounds, particularly solid cores with biopolymer protective materials, is limited by an incomplete understanding of the internal microstructure and protective layer architecture of microcapsules, due to the heterogeneity and complexity of multicomponent protective materials. Such understanding is critical for optimizing core stability, functionality, targeted delivery, and broader applicability. To address this, we applied an integrated approach using advanced structural and compositional techniques to examine the internal microstructure, core distribution, and protective layer architecture of model biopolymer-based solid-core microcapsules. Specifically, we focused on Lacticaseibacillus rhamnosus GG (LGG) probiotics (as the solid core) coated with softwood galactoglucomannans (GGM) and hardwood glucuronoxylans (GX), which are heterogeneous and multicomponent polysaccharides, to elucidate the formation mechanisms of microcapsules during spray drying. The results revealed hollow microcapsules, with smaller particles exhibiting thicker protective layers. LGG cells were embedded within the protective layers a few nanometers beneath the surface, physically interacting with lignin residues in GGM and GX, while the hollow cores were mostly empty. The average protective layer thicknesses (3.4 μm for LGG-GX and 3.9 μm for LGG-GGM) were sufficient to accommodate multiple LGG cells. These findings advance the understanding of microcapsule formation and structure-function relationships, supporting the design of stable, targeted probiotic/solid-core delivery systems and tailored biopolymer protective materials for food, pharmaceutical, and healthcare applications.