"Armor probiotic": Metal - Phenolic network and polysaccharide synergy for stress resistance and antioxidant activity

Probiotics provide significant health benefits to the host but often lose viability during processing, storage, and gastrointestinal transit, which limits their effectiveness. Single-cell encapsulation has emerged as an effective solution to overcome these limitations. In this work, a novel dual-component single-cell probiotics encapsulation called "armor probiotics" was prepared by integrating metal-phenolic networks (MPNs) (formed by ferric ions and gallic acid) with polysaccharides (hyaluronic acid or sodium alginate). SEM confirmed the formation of a uniform and continuous nanoscale "armor" around individual probiotic cells. It significantly enhanced viability (P < 0.05) under multiple stress conditions, including freeze-drying (92.67 ± 0.09 % survival without cryoprotectant), simulated GI digestion (84.28 ± 0.24 % viability), heat exposure, UV irradiation, and storage. The microcapsules also exhibited enhanced antioxidant activity, with a DPPH radical scavenging rate of 92.37 ± 3.14 %. The MPN-polysaccharide synergy enhanced intermolecular interactions, including hydrogen bonding, electrostatic forces, coordination bonding, and the viscous amorphous matrix, which were key contributors to the structural stability and protective performance. This study is the first to systematically demonstrate the cooperative role of MPN and polysaccharides in single-cell encapsulation of probiotics and to elucidate their underlying protective mechanism, which provides new technical approaches for the encapsulation and delivery of probiotics.