Deciphering the role of polyphenol types in the gelation behavior of Meretrix meretrix clam protein modulated by metal-phenolic networks.

Marine proteins are increasingly valued for sustainable food hydrogel design, yet their native gelation often yields insufficient mechanical performance and poor water retention, limiting practical applications. To address this gap, this study investigated the effects of four types of metal-phenolic networks (MPNs), assembled from copper ions (Cu2+) with epigallocatechin gallate (EGCG), tannic acid (TA), gallic acid (GA), and oligomeric grape seed procyanidins (OPC), on the gelation behavior of Meretrix meretrix clam protein (MMCP). Among them, the TA-Cu2+ and EGCG-Cu2+ delivered the most pronounced reinforcement, which significantly enhanced the hardness, chewiness, springiness, storage modulus (G'), and critical strain by 4.5%-73.9% relative to pure MMCP. The MPN incorporation also improved water-holding capacity by shifting water distribution from free to bound states. Furthermore, the MMCP/MPN composite hydrogels exhibited a compact gel network structure with reduced pore size and lacunarity, attributable to the formation of high-density multidentate coordination networks mediated by uniformly distributed Cu2+. The incorporation of TA-Cu2+ and EGCG-Cu2+ decreased the content of disulfide bonds while significantly enhanced hydrogen bonds by 28.3%-34.6% and hydrophobic interactions by 19.7%-27.6% in MMCP. Concurrently, this introduction drove a conformational transition from α-helix and random coils to ordered β-sheet structures through hydrophobic interactions and π-π stacking. These findings reveal the molecular basis of MPN-modulated marine protein gelation and establish a rational framework for designing novel hydrogels, enabling texture-enhanced seafood and controlled bioactive delivery in future foods.