Development of Meretrix meretrix clam protein/ι-carrageenan hydrogels with soft-textured and safe-swallowing: Insights into nonlinear rheological behavior, microstructure and gelation mechanisms

The complex coacervation and gelation behavior of Meretrix meretrix clam protein/ ι -carrageenan (MMCP/IC) influenced by various blending ratios (9:1-1:9) and pH (12-1) were investigated. Compared with other blending ratios, the MMCP/IC composite hydrogels at blending ratio of 4:6 exhibited the greatest rheological properties ( G' and G'' ) and textural properties (hardness, cohesiveness, springiness and chewiness), which were increased by 0.2-3.6 folds and 31%-151%, respectively. The MMCP/IC composite hydrogels showed weak strain overshoot behaviors and strain-softening behavior , which showed the best shear resistance and stability at blending ratio of 4:6 under large deformation. The P 21 and P 22 of MMCP/IC composite hydrogels at blending ratio of 4:6 enhanced by 3.3%-73.1% than that under other blending ratios compared with that of single MMCP. Correspondingly, MMCP/IC composite hydrogels at blending ratio of 4:6 exhibited a compact network structure with the lowest lacunarity and largest aggregation, supporting highest gel viscoelasticity. The strengthened electrostatic interactions and hydrogen bonds between MMCP and IC were reflected by blue shift of Amide A and Ⅰ bands, and the former occurred earlier than the latter. Furthermore, electrostatic interactions and hydrophobic interactions were the primary forces for maintaining MMCP/IC composite hydrogels, accounting for 25.6%-32.3% and 29.7%-40.6% of the total forces. The MMCP/IC composite hydrogels at various blending ratios (6:4, 4:6 and 2:8) could be classified into level 5 dysphagia food (minced and moist) by International Dysphagia Eating Standardization Initiative (IDDSI). These findings provide insights into the development of novel soft-gel types of dysphagia foods based on marine-derived proteins and polysaccharides.