This study has demonstrated that the extraction step is very important when analysing ATP and its degradation products. An important factor is whether the sample is fresh, frozen or thawed when homogenised since thawing of the sample will lead to rapid loss of ATP. During frozen storage it was found that ATP in cod (Gadus morhua) was stable at −40 °C in small samples for at least 12 weeks. At −20 °C it was found that ATP content increases initially and thereafter falls. It was demonstrated that degradation of ATP in small samples occurs faster at 0 °C than at −2 and −5 °C. Furthermore, it was found that in whole cod ATP could be synthesised at a significant rate at −7 °C. © 1999 Society of Chemical Industry

Variation in glycogen, ATP, and IMP contents within individual cod muscles were studied in ice stored fish during the progress of rigor mortis. Rigor index was determined before muscle samples for chemical analyzes were taken at 16 different positions on the fish. During development of rigor, the contents of glycogen and ATP decreased differently in relation to rigor index depending on sampling location. Although fish were considered to be in strong rigor according to the rigor index method, parts of the muscle were not in rigor as high ATP concentrations were found in dorsal and tail muscle.

No abstract

Changes in ATP, IMP, lactate and glycogen contents in the muscle of cod were followed during freezing at temperatures of −20C and −45C. ATP degradation was accompanied by a corresponding increase in IMP content. Simultaneous measurement of temperature showed that at both freezing rates, the greatest decrease in ATP content was observed when the temperature reached ‐0.8C. Glycolysis occurred during freezing of cod as indicated by an increase in lactate content. The changes found in all measured metabolites were more pronounced when freezing was performed at a slow rate compared to a fast rate due to the thermal arrest time at about 0.8C.

The ratio of pre rigor fish in frozen cod blocks was monitored. The fish (264 from 11 batches) was classified as either in rigor and post rigor or as pre rigor according to ATP and glycogen content. The average amount of pre rigor fish was found to be between 10 and 57% depending upon the criteria for determination of rigor state in frozen cod. The percentage of pre rigor fish in individual batches varied from a few percent to 100%.Principal component analysis of sensory and chemical data showed a correlation between gaping of the thawed fillet and the contents of ATP and glycogen. In conclusion, fillets from frozen whole fish with high content of ATP and glycogen (pre rigor) were more likely to gape when the fish was thawed at a high temperature compared to fish with high content of Ino and Hx (post rigor).