Freezing characteristics of fresh water fish (Labeo rohita) by liquid nitrogen vapor

The lean fish Labeo rohita was subjected to liquid nitrogen vapor in a batch freezer to determine its freezing characteristics. The moisture content of the fish muscle tissue was about 75%. The initial and average freezing points were found to be ? 1.34 and ? 5.25 °C, respectively. The fish slab sample showed a decreased rate of temperature change in that region. The suggested cut-off freezing temperature was ? 30 °C, corresponding to about 90% of total water frozen. Continued freezing below ? 30 °C resulted in negligible freezing of residual liquid water in the sample. The effects of low-density polyethylene (LDPE) bags and aluminum foil on the freezing times and the overall heat transfer coefficients were sufficiently small that the authors recommended thicknesses of up to 0.1 and 0.5 mm for LDPE bags and aluminum foil, respectively. In these cases there was only 5% increase in freezing time compared to unpackaged fish samples.