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Effect of brine- and plate-freezing at sea on chemical, physical, and organoleptic properties of three species of fish. Botta, Joseph Richard

Abstract

The effect of brine- and plate-freezing and length of subsequent frozen storage upon flesh pH, thaw drip, color, flavor, TBA (2-thiobarbituric acid) values, and long chain free fatty acids of Pacific halibut, Chinook and Coho salmon was determined. The effect of freezing method upon sodium, potassium, and chloride concentration was also determined. Flesh pH of all three species generally declined significantly (P ≤ 0.05) with length of storage. The thaw drip of Pacific halibut and Chinook salmon was less for the brine- than the plate-frozen samples after storage for 9 to 31 weeks whereas subsequently the brine-frozen samples had approximately equal or greater thaw drip than the plate-frozen. The thaw drip of all samples, except those from plate-frozen halibut, tended to increase with length of storage. The Hunter 'a' and a/b values of Chinook and Coho salmon generally increased during storage. The difference in flavor between brine- and plate-frozen outside muscle of halibut and Chinook salmon reached a maximum at 31 and 26 weeks of storage respectively, and then steadily decreased. In contrast, the difference in flavor between brine- and plate-frozen Coho salmon outside muscle steadily increased during storage. The difference in flavor between brine- and plate-frozen inside muscle of all species, except for the Coho salmon at 10 weeks and halibut at 31, 62 and 81 weeks of storage, was not significant. The difference in TBA values (an index of oxidative rancidity) between brine- and plate-frozen outside muscle samples rapidly increased and reached a maximum at 45, 26, or 27 weeks (the brine-frozen samples having the higher values) then decreased until there was approximately no difference at 81, 77 and 78 weeks of storage for halibut, Chinook and Coho salmon, respectively. Method of freezing or length of storage had little effect on the TBA values of inside muscle for all species. Method of freezing had little effect on the concentration of individual free fatty acids (percentage of total free fatty acids analyzed). The concentrations of several free fatty acids was affected by length of storage but the pattern of change during storage was erratic. Freezing method had an effect on the concentration of some individual free fatty acids (μ.g per gram of neutral lipid) of halibut and Chinook salmon but not of Coho salmon. In general, with all species, the concentration of the individual free fatty acids was greatest in the inside muscle. Also for halibut and Chinook salmon, particularly where there was a significant difference among storage times, the concentration of the free fatty acids rapidly increased during the first 26 to 31 weeks of storage. Method of freezing and length of frozen storage had a significant effect on total free fatty acids analyzed for only Chinook salmon. Total free fatty acids significantly (P ≤ 0.05) differed between inside and outside muscle of halibut and Chinook salmon but not of Coho salmon. The effect of method of freezing upon potassium concentration was small and varied with species. The effect of brine-freezing upon most variables measured was either small and/or complex. For all three species the sodium and chloride concentration was two to three times greater in the brine-frozen outside muscle than in all other samples. The taste panel results and the TBA values indicate that brine-freezing does impair the quality of the outside muscle of halibut and Chinook salmon during the early stages of frozen storage.

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