The present study involved the measurement of fish muscle texture by both objective and subjective means. Reliable methods for the evaluation of fish texture as well as interpretation of results are discussed. The study demonstrated that significant correlations between the methods could be achieved if carefully controlled conditions *were maintained. The presence of dimethylamine in frozen hake (Urophycis chuss) appeared to be a good chemical indicator of toughness whereas the extractable protein nitrogen was not as reliable. Data suggest that although the enzymatic formation of formaldehyde was a major factor in the toughening of red.hake, other factors probably contribute to the textural deterioration observed during cold storage. It is evident that haddock (Melunogrammus aeglefinus) toughens when stored at relatively high temperatures (-5°C) and like hake, experiences a loss of water-holding capacity although no formaldehyde accumulates in the tissues. The molecular basis of toughening in fish was examined by SDS gel electrophoresis. Apparently, the formaldehyde produced by the TMAO-ase enzyme system in red hake resulted in the covalent cross linking of troponin and myosin light chains, forming higher molecular weight aggregates. Changes at the molecular level were not detected by this method in haddock. Textural changes in this species are not as pronounced as those of hake and are most likely due to secondary bonds such as hydrogen or electrostatic.

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During frozen storage at −10 C, deterioration in muscle of silver hake (Merluccius bilinearis) was marked by rapid and extensive production of dimethylamine, concomitant decrease in extractable protein, and by lipid hydrolysis. Evidence of lipid oxidation in this gadoid species of relatively high fat content (2–4%) was also obtained. In minced flesh the rates of deterioration were about twice as fast as in fillets. Holding round fish for up to 6 days in refrigerated sea water (RSW) at 0–1 C before processing extended the frozen storage life of fillets at −10 C by 2–3 wk and of minced flesh by 1 wk over that for comparable materials prepared from round fish held in ice. Materials prepared from winter (March) and summer (August) fish showed little or no difference in rates of deterioration. The susceptibility of silver hake to deterioration at −10 C is similar to cusk; deterioration is faster than in cod or haddock, but not as fast as in red hake (Urophycis chuss). In all silver hake materials negligible deterioration occurred during frozen storage at −26 C for up to 6 mo.During preprocessing storage of round silver hake in RSW, a firm texture and acceptable appearance were retained for several days longer than in round fish held in ice, where objectionable softening of the flesh occurred, particularly in summer-caught fish. Saturation of the sea water with CO2 retarded the onset of bacterial spoilage in RSW-held fish, which otherwise developed more rapidly than in iced fish.

Dimethylamine (DMA) formation occurs in the muscle of silver hake (Merluccius bilinearis) during frozen storage. The rate of its formation in fillets and minced flesh during subsequent frozen storage for 1 mo at − 10 C is not affected by preheating at temperatures up to 60 C. Preheating to 80 C, however, greatly retards DMA development. Lipid hydrolysis (free fatty acid accumulation) is arrested by preheating to 60 C, but is little affected by preheating at temperatures up to 45 C. These deteriorative reactions are faster in minced flesh than in fillets, and in materials prepared from summer (spawning) fish than in those prepared from winter fish.In breaded fishery products, preheat treatment as presently practiced is insufficient to inactivate these deteriorative enzymic reactions in sensitive gadoid species such as the hakes and pollocks.

Refrozen silver hake (Merluccius bilinearis), processed as fillets and minced flesh after thawing of stored round fish that had been frozen within 14 h of capture, underwent rapid deterioration during storage at −18 °C compared with once-frozen control materials from the same lot of fish. The estimated maximum storage life of silver hake refrozen as fillets after 3 and 6 mo storage of the round fish at −25 °C was reduced to about 4.5 and 1 mo, respectively, from 10 mo for once-frozen control fillets. Quality of the refrozen materials immediately after thawing and refreezing was similar to that of the round-frozen fish, except after 6 mo, where some initial deterioration occurred, particularly in minced flesh. Minced flesh was more unstable in frozen storage than fillets. In all once- and twice-frozen materials, formation of dimethylamine occurred concomitantly with decrease in protein extractability. Round-frozen fish underwent no loss in protein extractability during 6 mo storage at −25 °C, but some lipid hydrolysis occurred. These results suggest that the freeze–thaw–refreeze process as applied to silver hake will yield a final product of acceptable quality provided that storage of the round fish does not exceed 3–4 mo and that the refrozen materials are marketed within a month after processing. Key words: silver hake, Merluccius bilinearis, refrozen storage, dimethylamine, minced flesh