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 plantarumeven 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.