Coumaric acid-induced spontaneous gelation of apple pectin with controllable structure and multifunctional properties

This study investigates the ability of p-coumaric acid (CA) to induce spontaneous gelation of low-methoxyl apple pectin (AP, DM 30%–40%) under sucrose-free, calcium-free, and heat-free conditions at pH 3.0, and characterize the structural, mechanical, and functional properties of the resulting composite hydrogels. Stable elastic-dominant hydrogels were formed at CA concentrations of 4–9 mg/mL, with a precisely defined critical gelation concentration of 4.0 mg/mL. Rheological measurements revealed that the storage modulus ( G′ ) increased from 0.48 ± 0.02 Pa in AP dispersion to 13.92 ± 0.10 Pa in composite hydrogels containing 9 mg/mL CA, accompanied by pronounced shear-thinning behavior and syringeability with long-term shape retention. The hydrogels exhibited tunable water retention and freeze–thaw stability, with CA incorporation significantly restricting water mobility in the network. Meanwhile, the composite hydrogels possessed robust antioxidant activity (DPPH: ∼90%; ABTS: >95%), broad-spectrum antibacterial effects against both Gram-positive and Gram-negative strains, and favorable growth compatibility with Lactobacillus plantarum even at the highest tested CA concentration (9 mg/mL). Multi-scale characterization and molecular docking indicated that hydrogen bonding between AP and CA was the primary drivers for network formation, with CA-mediated shielding of interchain electrostatic repulsion acting as a prerequisite for the ordered spontaneous self-assembly of AP chains. This work provides a novel, mild, and clean-label strategy to develop multifunctional AP–based hydrogels with controllable viscoelasticity and bioactivity, highlighting great application potential in food, biomedical, and packaging fields.