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.
Study of the rate and extent of octopine formation in ice-stored sea scallop meat (Placopecten magellanicus) confirms that it, rather than lactate, is a principal end product of carbohydrate metabolism in this species. Little or no octopine is detectable in fresh muscle dissected from live scallops, but on subsequent iced storage octopine accumulates, with reciprocal decrease in arginine, to maximum levels of about 1% in 6–10 days. An active octopine dehydrogenase, catalyzing the reductive condensation of arginine and pyruvate, was present, and lactic dehydrogenase activity was absent. Octopine accumulation occurs concomitantly with nucleotide degradation (dephosphorylation of adenosine 5′-triphosphate (ATP)). Its formation is linearly related to decline in muscle pH.Octopine production had usually attained its maximum considerably before the point of inedibility was reached; hence, the use of octopine content as an index of quality in scallop meats seems limited to the early postmortem storage period, as confirmation of freshness.
In scallop adductor muscle stored at 0 C, postmortem degradation of adenosine triphosphate (ATP), the predominant nucleotide at death, primarily follows the route ATP → adenosine diphosphate (ADP) → adenosine monophosphate (AMP) → adenosine → inosine → hypoxanthine (Hx). In one lot of scallops, however, inosine monophosphate (IMP) was present as an intermediate along with AMP. Hence, an alternate pathway, similar to that in fish muscle, whereby AMP is degraded to inosine and Hx via IMP rather than adenosine, may exist under certain (undefined) conditions. ATP dephosphorylation was much slower than in fish muscle; however, a rapid turnover of the intermediates in the degradative sequence, indicating relatively high activities of the enzymes catalyzing these reactions, resulted in the formation of appreciable amounts of Hx (3–4 μmole/g) within the edible storage period. In preliminary tests, taste scores correlated well with Hx contents, suggesting that measurement of Hx content may be a useful index of quality in scallop meats.Column chromatographic analyses showed that adenine nucleotides and their degradation products accounted for about 90% of the total acid-soluble purines and pyrimidines in scallop adductor muscle, with nicotinamide adenine dinucleotide and uridine diphosphate glucose as the principal minor nucleotide constituents. The muscle also contained considerable amounts of homarine (2–3 μmole/g). Glycolysis showed no relation to nucleotide degradation, both processes demonstrating a relatively slow postmortem catabolic rate in scallop muscle.
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.
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