|Amino acid composition of fresh fish and influence of storage and processing|
Bramstedt, F. (1962). Amino acid composition of fresh fish and influence of storage and processing, in: Heen, E. et al. Fish in nutrition. pp. 61-67
In: Heen, E.; Kreuzer, R. (1962). Fish in nutrition. Fishing News (Books): London. XXIII, 447 pp., more
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VLIZ: Biological Resources 
Recent investigation indicates that muscles of fish and shellfish contain large amounts of free amino acids, the pattern of which is characteristic for the different species. Great differences are seen in the amount of the free amino acids only. The protein-bound amino acids show a very uniform pattern. The uniformity of the pattern of free amino acids makes it possible to investigate the influence of factors such as storage, spoilage and processing on the composition of the free amino acids. Recent investigations showed that the proteolytic and peptidase enzymes in fish muscle play an important part in the degradation of proteins and peptides, especially during the initial stage of storage before the bacterial invasion takes place. Environmental conditions such as salt concentration of the sea water obviously influence only a few free amino acids probably those involved in osmo regulation. Glycine is an important factor for the individual taste of the flesh of different fish species. It seems, however, that there might also be a relation between the individual taste of fish species and the free amino acids in the flesh. Biochemical changes in the free amino acids of fish muscle have been found occurring in the early stages of ice storage even under optimal conditions on board modern fishing boats. Investigations showed, for example, that lysine was the subject of the greatest quantitative variations. For example, the content of free lysine in cod muscle increased from 3.73 mg. per cent in first-quality fish to 24.25 mg. per cent in fourth quality. In fish unfit for human consurnption the amount of lysine decreases in proportion as the malodorous substances increase. In order to obtain perfect preservation of fish flesh, it is essential to inhibit fish muscle enzymes. Although deep freezing is a very effective method for inhibiting enzymes, it was found that cod muscle enzymes were still active at -17°C. In ice storage the amount of free amino acids decreases until the fifth or seventh day, but increases when bacterial activities start. Investigations have shown that free β-alanine occurs in cod muscle just after the fish has passed rigor mortis, and that most of it derives from de-carboxylation of aspartic acid. Very little is known about the influence of various processing methods on amino acids in fish muscle, and further work is urgently necessary .The same applies to the action of fish muscle enzymes, especially during the initial stages of spoilage.