During frozen storage at −5 C, dimethylamine (DMA) was produced in the muscle of five gadoid species. The amount was lowest in haddock and increasingly higher in cod, pollock, cusk, and hake. When the dark lateral muscle was removed from the fillets before freezing, formation of DMA during frozen storage was either inhibited or greatly reduced. Under the same storage conditions no DMA was produced in the muscle of halibut, plaice, redfish, or wolffish.

In cod fillets undergoing deterioration during frozen storage, the dimethylamine content increases (and not the trimethylamine content as previously reported by us). There was no evidence to show an accumulation of dimethylamine in the muscle of frozen scallops, lobster, or shrimp that were purposely held at relatively high storage temperatures. It is suggested that for fish of the family Gadidae dimethylamine might be used as a measure of "frozen-storage deterioration" in much the same way as trimethylamine has been used as a measure of microbial spoilage in the unfrozen fish.

During frozen storage at −18 and −25 C the lipids in cod muscle did not undergo oxidation, as indicated by thiobarbituric acid values and odours. In fact they underwent a marked decrease in the ease with which they were oxidized by added Cu++, Fe++, or hemoglobin. This change preceded the protein denaturation that occurs in stored frozen muscle and appeared to be directly related to the formation of free fatty acids in the muscle. A similar change in the sensitivity to metal-induced oxidations could be produced in fresh, unfrozen muscle by the addition of mixed fatty acids prepared from several marine lipids.The addition of four pure saturated fatty acids had little or no effect on the development of rancidity in muscle, either in the presence or absence of added metal catalysts. Fish muscle appears to exert a protective action against the oxidation of added linolenic or linoleic acids. Unlike the mixed marine fatty acids, pure linoleic and linolenic acids did not suppress the development of metal-induced rancidities in fish muscle lipids.

1246Tnls note is concerned with a comparison of the effects of iced and frozen storage on production of trimethylamine (TMA) and dimethylamine (DMA) and decreases in extractable protein nitrogen (EPN) in fillets from four gadoid species. Though there is much in the literature on the production of TMA, there is little on that of DMA, and limited information on comparisons concerning DMA and EPN in iced and frozen fish.Materials and methods -Deep-sea Atlantic cod (Gadus morhua), pollock (Pollachius virens), cttsk (Brosme brosme), and hake (Merluccius bilinearis) were obtained from trawlers as they were being discharged on the wharf. They were immediately fi11eted and the opposite fillets from fish of each species were kept in separate piles. The fillets from the first set were individually packaged in heat sealed, laminated plastic pouches, frozen in a aNo J. D.lrs. 1973. Comparison of changes in trimethylamine, dimethylamine, and extractable protein in iced and frozen gadoid fillets. J' Fish.Res. Board Can. 30: 1246-1248.When flllets of Atlantic cod (Gadus morhua), pollock (Pollachius virens), cusk (Brosme brosme), and silver hake (Merluccius bilinearis) were iced and the opposite flllets frozen, large amounts of trimethylamine were rapidly produced in the iced fish but none was formed in the frozen fish within 60 days. Hake produced large, similar amounts of dimethylamine (DMA) in iced and frozen fillets. The other three species produced more DMA in the frozen than in the iced fillets, but always much less than in the hake. In both frozen and iced fish the production of DMA was accompanied by a corresponding decrease in extractable protein nitrogen. Casrnr,r,, C. H., W. E. Nrnr,, aNo J. Da.r,s. 1973, Comparison of changes in trimethylamine' dimethylamine, and extractable protein in iced and frozen gadoid fillets. J. Fish. Res. Board Can. 30: 1246-1248.Lorsque des filets de morue franche (Gadus morhua), goberge (Pollachius wrezs), brosme (Brosme brosme) et merlu argent6 (Merluccius bilinearis) sont p1ac6s dans la glace, et les filets oppos6s sont congel{s, il se produit de fortes quantit6s de trim6thylamine dans le poisson giai6, alors qo'il ne s'eniorme pas dans le poisson congel6, au cours d'une p6riode de moins de 60 jours. Le merlu argent6 produit de fortes quantit6s de dim6thylamine (DMA), les mOmes dans les filets g1ac6s et dans ies filets congel6s. Les trois autres espdces produisent plus de DMA dans les filets congel6s que dans les filets glac6s, mais toujours en quantit6s beaucoup moindres que chez le merlu argent6, La production de DMA, d la fois dans le poisson congeld et dans li poisson g1ac6, s'accompagne d'une diminution correspondante d'azohe prot6ique extractible.

Addition of free amino acids to blended cod muscle affected the subsequent development of rancidity. In the presence of trace amounts of Cu++, the aromatic, heterocyclic, and sulphur-containing amino acids exerted varying degrees of antioxidant acitivity. In the absence of added metallic ions the aliphatic amino acids and cysteine showed strong pro-oxidant activity. Tests were carried out to determine the effect of pH and the concentration of amino acid on these reactions.Amino acid-induced rancidity was inhibited by the commercial antioxidants NDGA, PG, and BHT and by the chelating agent, EDTA; but not by tocopherol; ascorbic acid enhanced the oxidation. A limited number of tests indicated that the fish muscle did not undergo a seasonal variation in sensitivity to the amino acid-induced rancidity, and thus differed from the Cu++-induced rancidity.Those amino acids which inhibited metal-induced rancidities did not retard rancidity induced by the addition of sodium chloride.