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Until now freezing has been one of the most important means of storing fish. Several investigators have tried to solve the problems connected with the changes in the fish protein during frozen storage (Cowie et al. 1966, Olley et al. 1967).Changes in the lipid fraction of the fish may be of equal importance in lowering the quality of the fish, especially fatty fish, during frozen storage. The purpose of this study was to examine the effect of two different storage temperatures and two different means of packaging upon the organoleptic quality and the fatty acid composition of frozen rainbow trout. Material and methodsThe experiments were carried out with second-summer rainbow trout fed with Clark dry food for rainbow trout. The average weight of the fishes was 130 grams (from 85 to 201 grams) and the control fishes were transported to the laboratory alive. The rest of the fishes were killed and gutted and frozen rapidly at -40°C. One half of the fishes were glazed with water while the second half was individually packed in vacuum sealed polyethylene bags. The fishes were then transported to the laboratory in styrox containers into which CO a-ice had been added. The fish arrived at the laboratory 18 hours after gutting. At the laboratory the samples were divided again into two halves with storage temperatures of 18 and 32°C. For the organoleptic evaluation samples were taken from the control fish after 1 day, 1 week, 1 month and 3 months, and for the fatty acid analyses from the control fish after 1 day, 1 week, 1 month and 7 months.The organoleptic evaluation was performed according to Niinivaara et ai. 1966, and the fatty acid analyses in accordance with the methods used in the previous study (Varesmaa et al. 1968).

Bacteriological spoilage, organoleptical quality and amino acid composition of fresh trout were studied during storage at +4– +6° C. Experiments were carried out with living fish (control), with fish 4 hours after killing and during storage. The fish were kept in air, in ice and packed in polyethylene and vacuum bags. It was observed that the type of packing considerably influences both the bacteriological and organoleptical quality. These changes were not, however, directly correlated with each other. In connection with vacuum packing, the amounts of anaerobic sulphide producing bacteria were so high that this aspect needs a detailed investigation before vacuum packing can be recommended for fresh trout. The amino acid composition of iced trout changed only slightly during storage. Current experiments concerning changes in volatile amino acid contents will provide additional information in this respect.

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