Partial freezing as a means of preserving fish freshness. I. Changes in free amino acids, TMA-N, ATP and its related compounds, and nucleic acids during storage.

Abstract

In order to develop a storage procedure to be used in place of iced or frozen storage for the preservation of fish freshness, partial freezing for periods of up to 2-3 weeks was examined using sea bass. The criteria for evaluation were made according to the changes in the amounts of free amino acids and trimethylamine nitrogen as well as post-mortem autodegradation of nucleotides and nucleic acids in fish muscle.The changes in the free amino acids of muscle during storage at -3°C differed significantly from those observed during ice storage, though no significant differences were observed between the muscles iced and stored at -2°C. During storage at -3°C, no appreciable amount of trimethylamine nitrogen was detected, initial spoilage of the fish being greatly reduced. The K value of fish muscle stored at -3°C reached 20% after 2 weeks, whereas that of iced muscle reached 58% in 5 days.The possibility that nucleic acids in fish muscle might be broken down to their mononucleotide constituents during ice storage or storage at -3°C was almost negligible as far as could be determined colorimetrically with the phloroglucinol reaction. However, degradation of nucleic acid molecules in iced muscle was indicated by the results of chromatography on methylated albumin kieselgur, whereas the degradation was reduced noticeably in muscle stored at -3°C.From the present results with sea bass, storage by partial freezing at -3°C seems to be effective as a means of preserving fish freshness when storage must be prolonged beyond the storage life of iced fish.