Metal-phenolic network-modified sodium caseinate/gellan gum hydrogels for enhanced probiotic encapsulation and...

Encapsulation is essential for protecting probiotics against harsh conditions during industrial processing and gastrointestinal transit. Gellan gum (GG) hydrogels offer good biocompatibility and colonic degradability, but their application in probiotic encapsulation is often limited by insufficient mechanical strength. To address this, we developed a composite hydrogel (SCM@G) by first forming a metal-phenolic network (MPN) through coordination between Fe³⁺, tannic acid (TA), and sodium caseinate (SC), and then incorporating the resulting SCM into a GG matrix. The gel properties, probiotic viability, and antioxidant capacity of SCM@G were evaluated. Results indicate that the MPN reinforcement significantly enhanced gel strength by increasing the crosslinking density, self-assembly ability, and structural stability of SC. This led to a 26.41% improvement in water-holding capacity and a 10.14-fold increase in storage modulus (G'), corresponding to a 5.76-fold overall enhancement in mechanical strength. The SCM@G hydrogel achieved a high encapsulation efficiency of 96.77% for probiotics and markedly improved antioxidant performance, with DPPH and ABTS radical scavenging rates increasing by 2.44- and 2.23-fold, respectively. After simulated gastrointestinal digestion, probiotic viability in SCM@G remained at 8.54 log CFU/mL, exceeding that of free cells by 3.37 log CFU/mL, indicating improved protection of probiotics during simulated gastrointestinal transit. This study constructs an MPN-SC-reinforced GG hydrogel encapsulation system and elucidates the mechanism by which MPN enhances gel performance. The high probiotic activity retained under simulated gastrointestinal conditions suggests that SCM@G offers a promising strategy for efficient probiotic encapsulation and protection.