Site-specific incorporation of sodium tripolyphosphate into myofibrillar protein from mantis shrimp (Oratosquilla oratoria) promotes protein crosslinking and gel network formation

Formation of protein gels in processed muscle foods is one of the most important functionalities. To explore the mechanisms responsible for affecting gel properties of muscle proteins by phosphates, myofibrillar protein (MP) from mantis shrimp (Oratosquilla oratoria) was treated with sodium tripolyphosphate at three pH values (7.0, 8.0, and 9.0). FTIR and UPLC-MS/MS firstly confirmed that phosphate groups were introduced to MP through C-O-P bonds via serine and threonine residues. The incorporation of STP caused increased electronegativity and solubility, more stable alpha-helix secondary conformation, and reduced tryptophan fluorescence intensity of MP, especially at pH 8.0 and 9.0. These changes led to a finer, ordered and denser three-dimensional gel network microstructure with higher gel strength and elasticity, and water-holding capacity. This study demonstrated that the introduction of phosphate groups could increase negatively charged residues in MP, enhance the crosslinks of proteins through ionic interaction, and promote gel network formation.