Water state and microstructure characteristics of surimi gel from silver carp with different processing conditions

To explore the mechanism of the quality improvement of low-salt silver carp surimi gel by ultra-high pressure processing (UHPP), we compared the differences of water state and microstructure among high-pressure processed low salt surimi gels (300 MPa, 1.5% NaCl), atmospheric low salt surimi gels (0.1 MPa, 1.5% NaCl) and controlled surimi gel (0.1 MPa, 2.5% NaCl) by analyses of low field nuclear magnetic resonance (LF-NMR), differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The results of DSC show that the freezing point of frozen water decreased but the bound water content increased significantly from 10.89% to 17.58% after UHPP treatment (P<0.05). The LF-NMR results demonstrate that the spin-spin relaxation time (T₂₁, T₂₃ and T₂₄) of low-sodium surimi gels after UHPP treatment decreased significantly (P<0.05), while the proportion of non-flowing water increased by 9.39% (from 67.29% to 76.65%). In addition, a smooth, uniform and denser network structure was achieved for low-sodium surimi gels at 300 MPa. Therefore, UHPP treatment (300 MPa, 10 min) can increase the bound water content and microstructure of low salt surimi gel.