Aim:
The present study aimed to enhance the quality of thawed Atlantic salmon by implementing sub-chilling prior to freezing.
Methods:
Eighty salmon (4-5 kg) were electrically stunned and bled commercially and divided into two equal-sized groups. The first group (ice) was packaged on ice in expanded polystyrene boxes, whereas the second group (RSW) was immersed in a premade refrigerated seawater (RSW)-cooling system, created by using a 7% NaCl brine and ice, holding ~-1.0°C. After chilling, the fish was hand-filleted and vacuum-packed (99% vacuum) before the fillets were randomized (20 fillets per group) into a factorial design following the fixed factors “chilling condition” (ice versus RSW) and “storage condition” (fresh, one-, and four-months frozen, respectively). The “storage condition” fresh was used as a control. The control groups (ice-fresh and RSW-fresh) were, after packaging, directly placed in the cold room (0.6±0.5°C) and evaluated through a 16-day storage experiment. The fillets to be frozen (ice and RSW, one- and four-months frozen, respectively) were flash-frozen (30 minutes) with dry ice (-78.5°C) before being stored in a freezer (-28.5±1.4°C). After frozen storage (one- and four-months), fillets were thawed in a water-bath (4°C) for 4 hours before being transferred to a cold room (0.6±0.5°C). The salmon fillet quality throughout the storage experiments (fresh and after one- and four-months of frozen storage) was evaluated by following the fillet drip loss, texture, and colour, as well as protein denaturation, adenosine triphosphate degradation, and microbial parameters on day 1, 5, 12, and 16 post packaging/thawing.
Results:
Sub-chilled fish (RSW groups) had a higher drip loss than those ice-chilled, with lower aerobic plate counts and higher concentrations of inosine monophosphate. Moreover, frozen fish showed a higher drip loss than the fresh controls, lower total viable psychotropic counts, surface-breaking force, firmness, chroma, and higher hue. All groups showed a decrease in quality through storage.
Conclusion:
It is concluded that sub-chilling prior to freezing improved the overall quality of fresh and frozen-thawed salmon fillets, whereas no effect of frozen storage time was observed.