Studies on the Irradiation Cleavage of Trimethylamine Oxide in Fish Flesh-I

Decomposition Products Found in Several Fishes

Abstract

The flesh of fish rich in the content of trimethylamine oxide (TMAO), such as cod, Alaska pollack, shark and cuttle fish were subjected to gamma-irradiation at dosages from 0.6 to 5.6 Mrad, to observe how TMAO, a specific constituent in marine fishes, would break down and if it would result in causing undesirable effects on the quality of the irradiated fishes.
Trimethylamine (TMA), dimethylamine (DMA), and formaldehyde (FA) were identified after irradiation in all the samples of the fish flesh and in TMAO solution as well. An increase in the amount of ammonia was detected in the same fish samples after irradiation, but very little amount in the irradiated TMAO solution (Table 3).
The difference in the quantity of TMA produced by the irradiation was not so apparent among the fishes examined. But, the difference in the quantity of DMA was apparent, i.e., the amount of DMA formed in the flesh of gadoid fish was larger than that in shark or cuttle fish (Fig. 1, Table 2). And, a remarkable difference in DMA level was noted between two individuals of Alaska pollack irradiated at the same dosage. A significant fact was that the amount of DMA in one of the irradiated flesh of Alaska pollack was extremely larger than that produced from pure TMAO solution under the identical condition of irradiation.
The precursor of FA formed by irradiation of fish flesh would not be limited to TMAO, however, a comparatively large amount of “free” FA recovered from the irradiated flesh of gadoid fishes was presumed to be derived from TMAO in the tissues (Table 4).