Nucleotide Degradation and Quality in Ordinary and Red Muscle of Iced and Frozen Swordfish (Xiphias gladius)

In iced dressed swordfish, inosine monophosphate, initially the predominant nucleotide (5.2 μmole/g), was dephosphorylated to inosine during 19 days storage. Hypoxanthine increased very slowly to about 1 μmole/g while quality (taste panel) showed no significant decrease to 15 days but was near borderline at 19 days. These changes occurred more slowly than in cod and related species. The sequence of nucleotide changes occurred much earlier in the red muscle. Rapid freezing and storage at −26 C for 4–5 months inhibited nucleotide enzymic activity, and quality remained unchanged. Slow freezing and storage for 1 week at −4 C significantly reduced quality to borderline or unacceptable levels, but only slightly affected the nucleotide degradation, indicating that other factors were responsible for the loss in quality. Dephosphorylation and hypoxanthine accumulation continued during further storage at −4 C. The levels of hypoxanthine reached during 19 days iced storage or 4–5 months frozen storage were not suffi...