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Summary Frozen fillets from cod which had been starved in an aquarium developed less cold store flavour or odour at −10°C than was developed by fed controls. Cis-4-heptenal, the major compound responsible for the off-flavour, was found to be present at a much lower level in the starved fish. At the same time the relative proportions of phospholipids and of the most important polyunsaturated fatty acids were found to be reduced by starvation. It was concluded that selective mobilization of precursors reduced the formation of the flavour compound during subsequent frozen storage. A seasonal variation in cold store flavour (and odour) therefore seems almost inevitable.

The post-mortem pH of cod muscle, which strongly influences its attributes as a food, is subject to seasonal variation. For most of the year the average of a batch lies above about 6.7, but for a short time in the summer it suddenly drops to low values, rising again just as suddenly. It is now thought that heavy feeding immediately after starvation causes this sharp fall. Fillets from fish frozen at such a time gape and have a tough texture after cooking. The low-pH period is fairly short, so cod are in fact suitable for freezing for all of the year outside certain summer months. The phenomenon has been observed in cod from a wide range of fishing grounds. Haddock show no such seasonal variation, but their post-mortem pH is lower on average than that of cod.

The post-mortem pH value of the muscle of cod, Gadus morhua L., is shown to be a valid indicator of the muscle glycogen level after rapid capture, stunning and rapid sampling (a level thought to be little different from that current before capture). Good correlations between initial glycogen values and post-mortem pH were obtained in fish of a wide range of nutritional states comprising fed, starved for different periods, and refed on different diets after starvation. Inconsistencies in results published in the literature are attributed to variations in the initial glycogen values as measured, which in turn stem from the fish struggling on capture, differing degrees of which reduce muscle glycogen by different amounts but probably do not affect the post-mortem pH. Variations in the time taken to sample the glycogen would also affect the results.

Revue bibliographique concernant les etudes de texture et d'ultrastructure et le comportement a l'homogeneisation a la congelation, a la decongelation, de chair de poisson (cabillaud). Analyses au niveau tissulaire et moleculaire (proprietes des proteines)

The viscosity of cod muscle, homogenised in 65% sucrose solution, was measured after the fish had been cold stored at-15° or -30° for various periods. The results differed according to the locality where the fish were caught, probably because of variations in the post-rigor pH of the muscle arising from differences in nutritional state. It was found that the values decreased during cold storage, and it was concluded that the method showed promise for assessing the texture of the fish after thawing and cooking.

The solubility of Lemon Sole muscle in 5% sodium chloride after storage at — 14 to — 15°C was shown to fall to the same minimum level as that of cod, but the reaction was very much slower. After storage for 5 years the protein had still been fairly soluble, and appeared to have reached the asymptote, but in the present experiment the fish were stored for over 17 years and the reaction was now evidently complete. It is complete in cod at this temperature in about 15 weeks.

Furan-containing fatty acids, which occur widely at a low level in fish lipids, become dominant in the liver lipids of starving cod.