Postmortem Physicochemical Changes in Unfrozen Newfoundland Trap-Caught Cod

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Abstract
Cod (Gadus morhua) caught in traps along the shores of Newfoundland are shown to be high in muscle glycogen, reaching a peak in late July and, unfrozen, reach a lower pH post-mortem than do cod caught in other Newfoundland fishing operations. Seawater temperature, muscle glycogen at death, and free drip developed in the fillets were minimal in June and maximal in late July. Fillets of these latter fish, after freezing during rigor, were of significantly poorer texture that those prepared earlier and later in the season.Fish which were not iced as soon as caught entered rigor mortis within 1 or 2 hr and although iced in the interim, were out of rigor in 24–36 hr. Fish iced at the trap were in full rigor 8–15 hr later; although rigor did not disappear completely for 70–90 hr, the fish could be filleted, by hand, in 24 hr.Generally, there were small weight losses in whole eviscerated fish not iced until several hours after capture but this weight was regained completely after 34 hr.Whole, eviscerated fish iced at capture developed less drip in the fillets than fish permitted to warm before icing. In fillets of fish in all stages of rigor there was a consistent trend for drip to increase with decreasing pH at filleting. The pH levels in turn were dependent on season of catch and on glycolysis after killing. In late midseason (August 2) catches, muscle glycogen appeared to be directly responsible for pH drop whereas in fish captured earlier, feed, physiological condition, and seawater temperature appeared to be the principal catalysts of pH change. Fillets prepared during rigor (August catches) showed no further drop in pH from that of the parent, iced material and developed 2–3% free drip in 24 hr; those processed before or after rigor mortis showed a further drop in pH from that occurring in the whole fish, and drip developed was much greater than in the samples filleted during rigor. Because considerable variability was noted in the rate of rigor development in any one catch, the particular state of rigor at filleting was found to correlate better with the amount of free drip in the fillets than was postmortem, age. The development and resolution of rigor in fillets was accompanied by considerable reduction in the solubility of the proteins (in 0.6 M NaCl solution), significantly more than in whole fish.If, for production reasons, trap fish must proceed into rigor before freezing, they should be chilled and stored in the whole, eviscerated state rather than as fillets.

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