Concentration of carbon monoxide in commercial fish flesh and in fish flesh exposed to carbon monoxide gas for color fixing

Abstract

A survey of the concentration of carbon monoxide (CO) in flesh from a variety of fish was conducted to see whether fish which had been exposed to CO gas could be detected. CO in fish flesh was obtained by head-space gas chromatography and determined after conversion of CO to methane with a methanizer. Concentrations of CO ranged from 3 to 12 μg/kg fish flesh, showing a narrow range in each species of fish except tilapia (Tilapia mossambica). CO was high in the red-flesh fish and low in the white-flesh fish. CO in sliced tilapia (a species of white flesh fish), however, ranged from 7 to 957 μg/kg. In tilapia, a high concentration of CO was observed in a sample in which the blood-colored parts of the slice were bright red, whereas the CO concentration was low in a sample in which the blood-colored parts were dark brown. The CO concentration in sliced tilapia containing 8 μg CO/kg increased to 234 μg/kg when the slice was exposed to CO gas. The blood-colored parts of the slice became bright red after the exposure. CO in the homogenate prepared from the CO-exposed sample decreased to less than 50 μg/kg within 4 days on storage in a refrigerator (5°C). The concentration of CO in the control increased slightly during this period. Among 19 commercial samples of tilapia, CO slightly increased in 5 samples containing about 10 μg CO/kg and decreased in 14 samples containing more than 50 μg CO/kg when the homogenate was kept at 5°C for 2 days. The blood-colored parts of the former group containing lower concentrations of CO were dark brown and those of the latter group containing higher concentrations of CO were bright red. The latter group of tilapia was suspected to have been exposed to CO gas.