Effects of different phosphorylation times and pH on fish gelatin: Functional properties, structural and mechanism analysis

This study aimed to investigate the functional and structural properties of phosphorylated fish gelatin (FG) with sodium pyrophosphate (STMP) through wet-heating under various wet-heating times (0.5, 1, 1.5, and 2 h) and pH levels (5, 7, 9, and 11), which was named as PT and PP group, respectively. Results showed that proper phosphorylation time and pH significantly enhanced the gel strength, emulsifying and foaming properties of FG, especially for the PT group. Rheological analysis showed that long phosphorylation time (1–1.5 h) and low pH (5–7) increased the apparent viscosity of FG, slightly increased gelling point and melting point. Environmental scanning electron microscopy revealed a uniform and denser microstructure in phosphorylated FG. Surface hydrophobicity and intrinsic fluorescence indicated that longer phosphorylation times led to increased exposure of hydrophobic and chromophoric groups, but this exposure was limited by phosphorylation pH. The FT-IR spectrum confirmed that the STMP phosphorylated FG by the formation of PO bond. LC-MS/MS analysis showed that the main phosphorylation sites of FG were serine, threonine and tyrosine. Overall, proper phosphorylation time and pH was an effective method for enhancing the gelling properties of FG. This study further deepens our understanding of the interaction between STMP and FG, and promotes the potential application of STMP to novel food products.