Effects of Different Freezing Methods on the Quality of Synechogobius hasta

To improve the quality of Synechogobius hasta during frozen-storage period, still air freezing, supply air freezing and liquid nitrogen quick freezing were used to treat fresh Synechogobius hasta, so as to study the effects of different freezing methods on the quality of Synechogobius hasta. Combined with ice crystal observation and sensory evaluation, cooking loss rate, total volatile basic nitrogen (TVB-N), thiobarbituric acid value (TBA), K value salt-soluble protein content and Ca²⁺-ATPase activity were used as physical and chemical indexes to investigate the quality changes of Synechogobius hasta during frozen-storage period. The results showed that the time for still air freezing, supply air freezing and liquid nitrogen quick freezing to pass through the maximum ice crystal formation zone was 315, 95 and 8.5 min respectively, and the time for liquid nitrogen quick freezing was the shortest (P<0.05). Compared with the other two freezing methods, liquid nitrogen quick freezing had less mechanical damage, fine and uniform ice crystals. During frozen-storage period, cooking loss rate, TVB-N value, TBA value and K value all showed an upward trend, and the rising rate of liquid nitrogen quick freezing was significantly lower than that of still air freezing and supply air freezing. Salt-soluble protein content, Ca²⁺-ATPase activity and sensory evaluation all showed a downward trend, with the fastest decline in still air freezing and the slowest decline in liquid nitrogen quick freezing. When frozen for 180 days, TVB-N value and K value of liquid nitrogen frozen Synechogobius hasta were 13.15 mg/100 g and 19.78% respectively, which reached the Grade I freshness standard, and the Grade II freshness was determined by supply air freezing and it was unfit to eat by still air freezing. Liquid nitrogen quick freezing can better inhibit protein freezing denaturation, fat oxidation and the effect of microorganisms, and better maintained the freshness of Synechogobius hasta. Liquid nitrogen quick freezing was better than supply air freezing and still air freezing with the best preservation effect, which can better maintained the quality of Synechogobius hasta.