CHEMICAL METHODS FOR THE DETERMINATION OF THE FRESHNESS OF FISH1 2

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Abstract
Various objective methods to estimate the degree of freshness of fish and fishery products were compared. The total volatile nitrogen (TVN) and ammonia-nitrogen of carp flesh reached values of 30–33 mg% when carp stored at 0.4°C. and 25–27°C. began to have a bad odor. For catfish stored at 0–4°C. and 25–27°C. these values reached 20–30 mg%. Trimethylamine was not found in fresh and spoiled carp and catfish. The determination of trimethylamine as an index of spoilage cannot be used for these fresh-water fish. The determinations of tyrosine and volatile reducing substances (VRS) cannot be used to estimate the degree of freshness of fish if the temperature at which the fish had been stored is not known. If these two methods were combined with TVN and ammonia-nitrogen one could determine the degree of freshness of fish and the temperature at which the fish were stored. The determination of tyrosine combined with TVN and ammonia-nitrogen can give further support as to whether fish are absolutely fresh. If the temperature under which fish have been stored is known each of the tests used in this study can be applied individually to determine the degree of freshness of fish.

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