Conditions for the effective chilling of fish using a nano-sized ice slurry

Abstract

Parameters for chilling fish using nano-sized ice crystals (NI) made from 3.6% salt water were investigated. Flake ice mixed with salt water (CS) was utilized for comparative purposes. The effect of ice : fish ratio (2:1, 1.5:1, 1:1) on chilling rates and on time, at, or below threshold temperatures (lowest achievable, 0 °C, and 4 °C) were investigated. Meltwater handling techniques were also investigated: initially drained (INIT), continuously drained (CONT), or non-drained (NODR). Ice : fish ratio did not significantly affect fish chilling time (p > .05). Increasing ice : fish ratio doubled time at or below 0 °C (11 → 24 → 41 hr) and increased it 1.5-fold for 4 °C (23 → 34 → 48 hr). Both NI INIT and CONT performed similarly as fish cooled to 0 °C. However, lowest internal fish temperature (–.81 °C) was achieved and fish were chilled for longer times at or below 0 °C and 4 °C with NI INIT. Practical applications Chilling and storage of fish in slurries of ice and seawater are common postharvest handling practices for fishing vessels. Chilling with a slurry ice is advantageous to solid ice because it more effectively interacts with the product surface to absorb heat. Limitations of slurry ice include the tendency of the ice to float to the container surface and form hard ice crusts. The resultant ice crusts have to be physically broken (usually with a shovel) by employees and this action often damages product. The nano-sized ice crystals in the slurry investigated does not create damaging ice crusts. It is also gel-like in texture and therefore less abrasive. Finally, it is created directly from salt water thereby negating the need for fishermen to buy their ice. The smaller ice crystal size, however, may result in more rapid melting and less effective chilling than more traditional slurry ice. The project demonstrated, that despite the small size of the ice crystals, this type of slurry ice is just as effective in chilling fish and keeping fish below temperature thresholds as currently commercially available ice slurries.