Physicochemical characteristics, gelation properties, and molecular mechanisms of grass carp (Ctenopharyngodon idella) myofibrillar proteins affected by the substitution of NaCl with CaHMB.

The construction of health-oriented fish protein products with desirable gel behavior as well as low salt content is urgently demanded by people nowadays. This study elucidated the substitution of sodium chloride (NaCl) with calcium β-hydroxy-β-methylbutyrate (CaHMB) in modulating the physicochemical and gel properties of grass carp myofibrillar proteins (gcMPs) at different substitution degrees. The results showed that the presence of CaHMB clearly reduced the fluorescence intensity and surface hydrophobicity of gcMPs, while increased their UV absorption intensity, representing the unfolding of gcMPs tertiary structure. Notably, the gelation performance of gcSGs was augmented by CaHMB substitution in a dose-dependent manner, with the G' increment folds of 3.7-7.9 in comparison to those of the control. The immobilized water was the dominant water population in gcMPs/CaHMB gels. Moreover, hydrogen bonds, electrostatic and hydrophobic interactions varied during gcMPs/CaHMB gel formation, as reflected by movements of O-H and N-H groups as well as amide I and II bands, with the O-H group changing first. The gcMPs/Ca-H gel system performed the most homogenous gel network, largest protein aggregates, and the highest surface roughness, as reflected by a 15.7%-48.7% increase in vessels percentage area, total number of junctions, and total vessels length and a 33.3% decrease in lacunarity compared with those of the control. Additionally, the grass carp myosin underwent obvious structural stabilization when substituted with CaHMB, being mainly related to protein-protein and protein-ion interactions according to molecular simulations. These results contributed to the development of low-sodium gcMPs gel products with superior gel characteristics and high nutritive values.