The changes which occurred in the concentrations of ATP, ADP, AMP, inosine monophosphate, inosine and hypoxanthine in skeletal muscle of rainbow trout, salmon and goldfish during the onset and resolution of rigor mortis were investigated. The effects of ante mortem handling and methods of slaughter on the concentrations of these nucleotides in muscle immediately after death and during storage of fish at 3° and at -30° were examined. Very careful handling of fish and killing by a method which did not cause contraction of muscle were essential if concentrations of ATP were to be at levels indicative of resting muscle (4 to 6∐mol/g tissue). Fish which were anaesthetised ante mortem and killed by cervical fracture or by clubbing had a high concentration of ATP and a relatively slow onset of rigor. Fished slaughtered by CO2 stunning or asphyxiation struggled violently at death and the muscle had very low concentrations of ATP, very high concentrations of inosine monophosphate and rapid onset of rigor. The ratio of the sum of the concentrations of inosine and hypoxanthine to the total concentration of the six nucleotides was used as a criterion of freshness. Quality and freshness were also evaluated by physical and sensory procedures, texture by measurement of muscle shear force and freshness by measurement of the dielectric constant of the whole fish and by a standard method of visual appraisal of the fish. The results demonstrated that there is a relationship between biochemical data, texture, dielectric constant and visual evaluation for both fresh chilled) and frozen fish. During rigor, the resolution of rigor and in the post rigor state freshness and quality declined on the basis of an increase in K value and a decrease in shear force, dielectric constant and visual assessment. There were significant differences in all four assessments of quality between fish which died tranquilly (clubbing) and those which struggled during asphyxiation. The slaughter procedure therefore appears to have an influence on several aspects of quality in fish during storage at 3°C and -30°C.
free text keywords: fish, muscle, skeletal, adenosine triphosphate, adenine nucleotide metabolites, texture, quality, Biochemistry, Biophysics, and Structural Biology