During the summer of 1986, the Utilization Research Division of the Northwest Fisheries Science Center entered into a cooperative agreement with the Alaska Seafood Marketing Institute (ASMI) to study how time and temperature affect the quality and acceptability of pink and coho salmon (Oncorhynchus gorbuscha and O. kisutch, respectively) held on ice and in frozen storage. Changes in the quality of the salmon were determined by chemical, microbiological, and physical analyses which were correlated with results of sensory evaluations made by an experienced taste panel familiar with salmon.
Special emphasis was given to determining the maximum period that both species of salmon could be held refrigerated on ice before losing those characteristics typically associated with premium quality and to follow changes in the quality of those salmon during subsequent frozen storage. Results from these studies were compared to analytical and sensory results from a corresponding study to follow changes in the quality of pink and coho salmon frozen shortly after harvest.
Results of sensory analyses of the iced salmon indicated that both the pink and coho salmon retained their prime quality characteristics for about 8 days postharvest.
Multiple chemical indicators were used in this study to determine freshness or lack of freshness. Inosine monophosphate (IMP) levels in premium quality iced pink salmon ranged between 3.5 and 5.0 micromoles per gram, hypoxanthine (Hx) content ranged between 0.2 and 0.7 micromoles per gram, and trimethylamine (TMA) content was less than 0.4 mg nitrogen per 100 gram. IMP content in premium quality iced coho salmon ranged between 2.5 and 4.0 micromoles per gram, and less than 1.0 micromole per gram of Hx was detected. Premium quality coho salmon contained less than 1.0 mg per 100 grams of TMA.
The chemical indicator for oxidative rancidity (thiobarbituric acid number) in premium grade iced pink and coho salmon did not exceed 2.5 micromoles malonaldehyde per 100 grams in this study.
Premium quality iced salmon were characterized by low bacterial count (i.e., 2.8 to 6.7 x 103 no. per cm2).
After 3 months in frozen storage at -23¿C, the sensory scores for the pink salmon stored on ice prior to frozen storage or frozen immediately on landing indicated the fish were of acceptable, but less than premium quality because of rancidity. The quality of the pink salmon reference stored at -29¿C was considered organoleptically and chemically premium grade through 9 months of storage.
Overall, the subjective quality of both the coho salmon frozen at point of landing or held on ice prior to frozen storage at -23¿C remained premium grade for 6 months. The quality of the reference coho salmon after 1 year at -29¿C was superior to that of the coho salmon stored at -23¿C.
Tests for chemical rancidity generally reflected the organoleptic condition of the frozen pink and coho salmon in this study.
Results of cook-drip analyses showed that both species of salmon were affected by both storage on ice and by time in frozen storage, but cook drip was not greatly influenced by differences in storage temperature