Changes in baseline levels of nucleotides during ice storage of fish and crustaceans from the Portuguese coast

Adenine nucleotides and related compounds were measured in North Atlantic hake, monkfish. rockfish, Norway lobster, and red shrimp from the South of Portugal immediately after catch and after a 72-hours ice storage period. To preserve the samples until analysis, a freezing technique with liquid nitrogen was developed and data compared with those from immediate extraction. The use of plastic vials in liquid nitrogen freezing gave similar data as when immediate post mortem extraction was done. Inosine monophosphate (IMP) was the main nucleotide present in the fish species, whereas adenosine monophosphate (AMP) was the major component of crustaceans. During ice storage of fish, adenine nucleotides were almost completely converted to IMP. Rockfish showed a significant catabolism of IMP with conversion to hypoxanthine (Hx). Red shrimp and, especially Norway lobster presented an important transformation of AMP into IMP. In general, Hs was either not detected (crustaceans) or was present in very low amounts, the highest levels being detected in rockfish after ice storage. This species presented also after 72 h the highest K value (58%), whereas in the other cases the values ranged between 7% and 11%. Trigonelline (Trigo), a UV-absorbing betaine, was also present in both crustacean species together with adenosine triphosphate (ATP) and related compounds.