Effect of Liquid Immersion Freezing Temperature on the Frozen Storage Stability of Snakehead (Channa argus) Fillets: Water Retention, Protein Secondary Structure, and Ice Crystal Morphology

This study investigated the effects of freezing method and temperature on the quality stability of snakehead fillets during frozen storage. Fillets were subjected to air freezing (AF) and liquid immersion freezing (LIF) at −20 °C, −40 °C, and −60 °C, followed by storage at −30 °C for 6 months. Results showed that freezing caused a reduction in hardness, an increase in water loss, and significant changes in protein secondary structure compared with fresh samples. Compared with AF at the same freezing temperature, LIF produced smaller ice crystal areas and diameters, suggesting reduced freezing-induced structural damage. During storage, overall quality progressively declined, as evidenced by increased water loss, decreased hardness, pH changes, alterations in protein secondary structure, and ice crystal enlargement. Among all treatments, AF-20 exhibited the most severe quality deterioration after 6 months of storage, whereas LIF-40 and LIF-60 showed better quality retention. Although LIF-60 generated the smallest ice crystals, LIF-40 also effectively reduced thawing loss and total weight loss during storage. These findings suggest that liquid immersion freezing at appropriately low temperatures can improve the frozen storage stability of snakehead fillets, with LIF-40 and LIF-60 showing favorable quality retention during prolonged storage.