[Determination of K-value and histamine of mackerel and tuna, by using the oxygen-sensor method]

Determination of K-value (fish freshness index) and histamine (Hm) of mackerel and tuna during storage at various temperatures was done by using the oxygen-sensor method. Hm in mackerel increased even at low temperature (5 degrees C), and reached the Defect Action Level (DAL) of the U.S. FDA, 5 mg/100 g, before the K-value approached the inedible level. As the storage temperature was increased, the rate of Hm formation increased remarkably and the amount of Hm in fish meat passed through the DAL, and reached the real hazard level, AL (50 mg/100 g), in a short time. The initial Hm level of raw tuna was too low to determine by our oxygen-sensor method, and the final Hm level after 8 days' storage at under 5 degrees C was only 0.6 mg/100 g. But, when the storage temperature was elevated, the rate of Hm formation increased rapidly, as in mackerel, and the Hm level reached the DAL, then the AL, in a short time. Simultaneous determination of K-value and Hm is recommended for accurate and reliable quality inspection of fish and fish products.