Effect of liquid nitrogen spray freezing conditions - temperature, sample volume and exposure depth - on the resulting temperature fluctuation, microstructure, and quality of large yellow croaker fish during frozen storage

Abstract

The microstructure and physicochemical properties of large yellow croaker (Larimichthys crocea) fish frozen by air freezing (AF, −20 °C) and liquid nitrogen spray freezing (LNSF) at −20, −60, and −100 °C, during frozen storage at −30 °C were evaluated. LNSF at −100 °C resulted in small and uniform ice crystals with a significantly (P < 0.05) lower cross-sectional area (187 μm²) as compared to AF (7844 μm²), thereby better preserving the structure of myofibrils, and reducing the thawing loss from 11.6% to 7.0%. The rate of lipid oxidation and protein degradation significantly decreased with an increasing freezing rate. The effects of sample volume and depth on temperature fluctuations and changes in the ice crystal size were explored based on changes in the ice fraction. The temperature fluctuations decreased from 0.94 to 0.65 °C, and the cross-sectional area decreased from 457 to 287 μm², as the product depth increased from 2 to 20 mm. Therefore, the sample volume, depth, and freezing temperature had significant effects on the microstructure and quality deterioration. LNSF at −100 °C effectively maintained the best quality and longest shelf life of frozen large yellow croaker.