Abstract: To enhance the gastrointestinal tolerance and antioxidant activity of Bifidobacterium longum subsp. longum T4, a singlecell encapsulation system designated T4@epigallocatechin gallate (EGCG)-Fe3+@LMP was constructed using a metal-phenolic network (EGCG-Fe3+) and low-methoxy pectin (LMP) as wall materials via layerbylayer selfassembly. The physicochemical properties of the system were characterized by particle size, zeta potential, ultraviolet (UV)-visible spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and confocal laser scanning microscopy (CLSM). The results showed that after encapsulation, the particle size of bacterial cells increased from 1 929.33 to 5 705.00 nm, and the zeta potential from −20.94 to −18.43 mV. Microscopic observations confirmed the successful formation of the encapsulation system, and XPS analysis verified the presence of Fe3+ in the system. In simulated gastric and intestinal fluids, the survival rates of T4@EGCG-Fe3+@LMP were 4.94 and 53.68 fold higher than those of free bacterial cells, respectively. Moreover, the scavenging rates of T4@EGCG-Fe3+@LMP against 1,1-diphenyl-2-picrylhydrazyl (DPPH), superoxide anion, and hydroxyl radicals all exceeded 70%, and its antioxidant activity was significantly higher than that of free bacterial cells (P < 0.05). In summary, this study not only provides an effective encapsulation strategy to improve the gastrointestinal tolerance and antioxidant capacity of probiotics, but also offers new insights into probiotic encapsulation technology based on the synergistic effect of metal-phenolic-polysaccharide networks.

Key words: Bifidobacterium longum subsp. longum; metal-polyphenol network; epigallocatechin gallate; low-methoxy pectin