Condition of Newfoundland Trap-Caught Cod and Its Influence on Quality After Single and Double Freezing
Authors: MacCallum W. A. , Jaffray June I. , Churchill D. N. , Idler D. R. 
Published: April 2011

Quality assessments, based on organoleptic evaluations and chemical tests, were conducted before and after cold storage, on trap-caught cod (Gadus morhua) which was unfrozen, once-frozen, or twice-frozen. The cod was processed both before and during rigor, after icing or after handling without ice, at various times during the catching season.Lactate determinations and pH measurements on whole fish at killing showed a seasonal variation. There was a correlation between lactate determinations and pH measurements in freshly killed and freshly frozen fillets that had been frozen both before and during rigor. Icing immediately after killing slowed the rate of lactate accumulation.Differences in the state of pre- and in-rigor chilled fish at freezing, as assessed by muscle glycogen, lactate, and reserves of ATP, resulted in differences in texture, thaw-drip, and pH. Patterns in texture may be predicted by the amounts of thaw-drip and the pH measured in the cold-stored pack.Intensity of mealiness and short-grained features in freshly frozen (once) fish was correlated with the level of ATP immediately before cooking. Fillets frozen before rigor toughened very slowly in storage at −23 C and the mealy condition eventually disappeared. Hence, fish downgraded for mealiness at freezing improved or maintained initial overall texture scores during 6 months in storage. Although the panel showed a clear preference for fish frozen pre-rigor, it would be impossible for industry to freeze more than a portion of the landings pre-rigor. To obtain the next best once-frozen product, chilled in-rigor fish should be processed.Double freezing gave the next best product from chilled, prerigor fish. Fish frozen pre-rigor in the "dressed" condition and stored at −23 C, then thawed, processed, and refrozen at 16 weeks, was equal in quality to once-frozen controls. The texture in the twice-frozen material prepared from iced, prerigor frozen fish dropped after a further 10 weeks storage, making it little better than the twice-frozen product of commercial-like handling. A very satisfactory twice-frozen product was obtained also by holding unfilleted blocks of non-iced, gutted fish at −46 C before thawing and refreezing, followed by remaining storage at −23 C. However, such low temperature storage is not within the scope of present commercial operations.With pre- and in-rigor frozen material a correlation was found between thaw-drip and pH, thaw-drip and overall texture (in-rigor freezing only), pH and overall texture values, and between pH and toughness. There was also a correlation between extractable protein nitrogen (EPN) values and overall texture scores of fish frozen in various stages of rigor (encountered during unfrozen storage of upwards of 24 hr before processing) but not between EPN and overall acceptability. With twice-frozen fillets prepared from material also handled unfrozen as above, there was significant correlation between EPN values at tasting and overall texture scores and between EPN and overall acceptability scores.Free fatty acid (FFA) values of the trap fish were high and showed no increase as the result of thawing and refreezing or further storage at −23 C or with pre- and in-rigor freezing. Storage at −46 C resulted in less FFA development. There was significant correlation between EPN and FFA values for June-caught once-frozen fish and between FFA values and strictly taste scores for June and July fish but no correlation between FFA and overall texture scores, or in the case of twice-frozen fish of any particular pre-freezing treatment, between FFA and taste, overall texture, or overall acceptability.