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Chemical changes that occur in the proteins, nucleotides, and lipids of fish tissue during storage at low temperatures were investigated. Homogenized tissue, prepared from fresh rock-fish (striped hass, Roccus species), was stored up to six days at temperatures from -10° to 4°C and then analyzed. At 0°C and below, the solubility of myofibrillar proteins decreased. There were also changes in polyacrylamide gel electrophoretic patterns of protein extracts. The total nucleotide content decreased rapidly at all temperatures. The lipids were extracted from each sample and separated into neutral lipids, phospholipids, and free fatty acids by column chromatography. The fatty acid composition of each fraction was determined by gas chromatography. In the fresh tissue, polyunsaturated acids occurred in greatest proportion in the free fatty acid and phospholipid fractions, whereas inono-unsaturated acids were inofe highly concentrated in the neutral lipids. The percentages of saturated acids were approximately the same in all fractions. During storage, there were considerably larger losses of individual acids from phospholipids than from neutral lipids. The polyunsaturated acids of the phospholipid fraction were affected most. Over 10% of these aeids were lost in six days at ice temperature, but only a small proportion of the losses was accounted for by increases in free fatty acids. Oxidative proo esses may account for the imbalance because the rate of oxidation, as measured by the thio-barbituric acid test, increased with storage temperature in the same manner as the rale at which unsaturated fatty acids were lost from the pliospliolipuls. Losses of polyunsaturated acids from the neutral lipids were much smaller, suggesting a selectively protective mechanism or environment in that fraction. The changes in the phospholipid fatty acids may provide the basis for useful objective tests of fish lecomposilion.

The stability of fish lipids during storage of fish tissue at ice temperature was investigated. Homogenized tissue from rockfish (striped bass, Roccus species) was stored 16 days at melting ice temperature. Lipids were extracted at intervals and separated into various components by silicic acid column chromatography. Changes in the weights of individual lipid components were correlated with gas chromatographic data on changes in individual acids of these components. In the fresh tissue, the phospholipid fraction contained the highest proportion of polyunsaturated acids and the neutral lipid fraction contained the highest proportion of monounsaturated acids. During storage of the tissue, there were decreases in the weights of total phospholipids and neutral lipids and an almost equivalent increase in the amount of free fatty acids. Although there were changes in all acids during storage, the polyunsaturated acids, eicosapentaenoic (C20:5) and docosahexaenoic (C22:6), were affected most and were lost at a faster rate from phospholipids than from neutral lipids. The loss of polyunsaturated acids was apparently by a selective process because most of the loss was from the cephalin fraction, even though it contained only about ¼ of the total polyunsaturated acids. Relatively small amounts of these acids were lost from the neutral lipids and virtually none from the lecithin.