SUMMARY– In order to assess green meat of tuna in preparation for canning, it is necessary to determine the trimethylamine oxide (TMAO) content of the raw meat.A simple and rapid TMAO determination method combined with a reduction method, which converts TMAO to trimethylamine (TMA), was developed. Using this method, the distribution of TMAO content in the muscles of yellowfin tuna was investigated to determine the most suitable sampling portion of the fish.A recommended practical method of sampling and determining TMAO for assessing green tuna is presented.

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SUMMARY– To predict green tuna after cooking, a practical measurement to select green tuna using 100 pieces of iced and clipper‐frozen yellowfin tuna was discussed. The most suitable sampling portions, the lowest level of trimethylamine oxide (TMAO) and the total trimethylamine content (TTMA) in tuna muscles were examined. It was recognized that the prediction of green tuna after cooking would be possible by determining TTMA content at the superficial layer of the central dorsal raw muscle (E portion). The lowest level of TMAO‐N was 8–9 mg%, and that of TTMA‐N was 11–12 mg% in an iced and 9 mg% in a clipper‐frozen green tuna. The predictive measurement accuracy was 96% on the lowest level of TMAO‐N or TTMA‐N.

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