Effect of Liquid Nitrogen Freezing Temperature on the Muscle Quality of Litopenaeus vannamei

Abstract

The implications of different liquid nitrogen freezing (LNF) temperatures (-35 °C, -65 °C, -95 °C, and -125 °C) on the ice crystal and muscle quality of white shrimp (Litopenaeus vannamei) were investigated in this essay. The results showed that better muscle quality was maintained after LNF treatment compared to that after air blast freezing (AF) treatment. As the freezing temperature of liquid nitrogen decrease, the freezing speed accelerated, with the freezing speed of LNF at -125 °C being the fastest. However, an excessively fast freezing speed was not conducive to maintaining the quality of shrimp. Among all the freezing treatments, LNF at -95 °C led to the lowest thawing losses and cooking losses, and the highest L* values, indicating that LNF at -95 °C could keep the water holding capacity of frozen shrimp better than that with other freezing methods. At the same time, LNF at -95 °C resulted in higher water holding capacity, and hardness values for shrimps than those with other frozen treatments (p < 0.05). In addition, the results of the water distribution of shrimps showed that treatment with a -95 °C LNF reduced the migration rate of bound and free water. Meanwhile, the microstructural pores of shrimps in the -95 °C LNF group were smaller, indicating that the ice crystals generated during -95 °C LNF were relatively smaller than those generated via other frozen treatments. In conclusion, an appropriate LNF temperature (-95 °C) was beneficial for improving the quality of frozen shrimp, and avoiding freezing breakage.

Keywords: Litopenaeus vannamei; ice crystal; liquid nitrogen freezing; muscle quality; temperature.

Figure 1

Freezing curves of vannamei shrimps at different LNF temperatures (A), and freezing curves of vannamei shrimps at −35 °C AF (B).

Figure 2

Changes in thawing loss (A), cooking loss (B), water holding capacity (C), and hardness of vannamei shrimps with different frozen treatments (D). Different letters indicate a significant difference (p < 0.05).

Figure 3

Changes in water properties in vannamei shrimp muscle under different frozen treatments. T₂ relaxation times (A); different types of water content (%) (B); T_2b1 relaxation times (C); T_2b2 relaxation times (D); T₂₁ relaxation times (E); T₂₂ relaxation times (F); false-color images obtained via T₂-weighted magnetic resonance imaging (G). The velocity bar right shows the correspondence between proton signal intensity and color, the weakening of the proton intensity corresponds to a gradual reddening of the colour of the bands. P_2b1, P_2b2, P₂₁, and P₂₂ represent the content of strongly bound water, weakly bound water, immobilized water, and free water, respectively. Different letters in the same index indicate a significant difference (p < 0.05).

Figure 4

Light microscopy images (magnification: 400×) of vannamei shrimp muscles under different frozen treatments.

Figure 5

Scanning electron microscopy images (magnification: 100×) of vannamei shrimp muscles with different frozen treatments (A); SEM image of ice crystal area distribution statistics (B).