Effect of Low-salt Curing on the Quality of Crisp Grass Carp after Freeze-thaw Treatment

To investigate the effect of salt concentration on the quality and myofibrillar protein of crisp grass carp fillets before and after a single freeze-thaw cycle, fillets were marinated in 0.25, 0.5, 0.75, 1.0, 1.5, and 2.0 mol/L NaCl solutions at 4 ℃ for 2 h. Following a 24 h freezing period, water-holding capacity, color, lipid oxidation, carbonyl content, total sulfhydryl content, SDS-PAGE profiles, microstructure, and myofibrillar protein structure were evaluated. It was found that fillets retained water better when the salt concentration ranged from 0.5 to 0.75 mol/L. The fillets exhibited a relatively tight tissue structure before and after freezing and thawing when the salt concentration was less than 1.00 mol/L. With increasing salt solution concentration, the L* value of fish fillets after freeze-thawing was higher than before freeze-thawing. Lipid oxidation and protein oxidation of fish fillets increased after freezing and thawing. SDS-PAGE analysis revealed that myofibrillar protein degradation increased before freezing and thawing with salt concentrations >1.5 mol/L. The degree of myofibrillar protein degradation remained stable after freezing and thawing when the salt concentration was <0.75 mol/L. Raman spectra showed that the α-helix content of fish fillets was significantly reduced, and the degree of protein degradation was intensified before and after freezing and thawing when the salt concentration was >0.75 mol/L. In conclusion, when the salt concentration is ≤0.75 mol/L, the quality of crisp grass carp fillets changes little before and after freezing and thawing, which can delay the oxidative degradation of proteins.