In the previous paper, it was reported that the amount of DMA produced during gammairradiation was higher in the flesh of gadoid fishes than that in shark or cuttle fish, and, in some case, it was even higher than the amount of DMA found in pure TMAO solution irradiated under the identical condition. A certain agency was supposed to be involved in this extraordinarily large quantity of DMA formation.
The tissues of gadoid fishes, especially the viscera, have been known to bear an enzyme system able to convert TMAO into DMA and formaldehyde. In this context, the authors presumed that the enzyme might be concerned with DMA formation in gadoid fishes as a promoting factor during the irradiation. The presumption mentioned above was likely supported by the following findings of experiments mainly on cod flesh-cod viscera mixture (20:1) as samples subjected to irradiation at 3.0 Mrad.
1. The formation of DMA during the irradiation in cod or Alaska pollack flesh revealed a marked acceleration by the addition of the viscera of these fishes, especially by cod pyloric coeca (Figs. 1 and 2). A similar acceleration effect was also observed in the samples which consisted of horse mackerel flesh or TMAO solution and cod pyloric coeca (Figs. 6, 7 and 8).
2. The “acceleration effect” never occurred when the pyloric coeca was heat-processed before adding it to the flesh (Fig. 4).
3. The “acceleration effect” was very weak or scarcely observed in a test when cod flesh was mixed with each pyloric coeca of horse mackerel, skipjack and gurnard or hepatopancreas of carp; these tissues were assumed to possess very low level or none of the enzyme activity concerned with DMA formation from TMAO (Fig. 5).
No “acceleration effect” was observed when the irradiation on flesh or pyloric coeca was conducted separately, or either of these materials was irradiated alone, prior to the preparation of the mixture (Tables 2 and 3). In other words, the acceleration occurred during the irradiation only and not after the irradiation. This may suggest that the acceleration should be dependent on the active role of free radicals generated during the course of irradiation.