Internal-external dual cross-linked alginate/gelatin composite hydrogel beads: Structure and pH-responsive gastrointestinal delivery of bioactives.

This work presented a novel stimuli-responsive sodium alginate (SA)/gelatin (Gel) dual cross-linked composite hydrogel beads using Rana chensinensis ovum protein hydrolysate calcium chelates (RPH-Ca) as a unique internal cross-linker to synergize with external calcium. The optimal mass ratio of SA to RPH-Ca was determined at 1:0.5. FTIR and XRD analysis revealed that the beads were stabilized by hydrogen bonding and ligand coordination, forming an amorphous system. The beads exhibited significant pH-responsiveness, with minimal release in simulated gastric fluid (<20%) and controlled, sustained release in simulated intestinal fluid (>95%). High encapsulation efficiencies for curcumin (94.66% ± 0.05%) and rhodamine B (96.84% ± 0.03%) demonstrated capability for simultaneous delivery of lipophilic and hydrophilic bioactives. Release kinetics analysis showed that curcumin followed super Case-II transport, while rhodamine B exhibited composition-dependent release, near-zero-order release in SRGHB3 and non-Fickian transport in SRGHB4. By integrating dual cross-linking, this work demonstrated a promising strategy for constructing smart delivery vehicles for food bioactives.