Adenosine triphosphate breakdown products as a freshness indicator of some fish species and fish products

The breakdown products of adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), inosine monophosphate (IMP), inosine (Ino) and hypoxanthine (Hx) of some fish species and heated fish products were determined by high-performance liquid chromatography (HPLC) and rapid paper strip method. The K value, calculated from ATP degradation products, the percent of the sum of Ino and Hx divided by the sum of ATP, ADP, AMP, IMP, Ino and Hx increased almost linearly in the muscle of all Finnish fish species studied, when stored on ice. There were some variations of K value among fish species and also between individuals of the same fish species, while Kvalue did not depend on the location of whitefish fillets. The K value of cold smoked rainbow trout increased similarly to that of unheated fish. In hot smoked fish (whitefish, mackerel and rainbow trout) the K-value increased during heating but not at all after subsequent storage in a chill room. The sous vide (final internal temperature 73°C) treated whitefish behaved like the hot smoked fish species. The K value of rainbow trout increased more slowly during heating than the K value of other fish species (Baltic herring, whitefish and mackerel) and in the case of the hot smoked rainbow trout the K value could be an indicator of the freshness of the raw material used. The low K value could possibly be used as evidence of really fresh fish. The K value was used as a criterion when comparing the effects of catching method on the quality of Baltic herring. The K values of gillnet-caught fish were greater than those of fish caught by trapnet or by trawling. The duration of trawling time (2 h and 5 h) did not effect the K value when the water temperature was 8–16 °C.