1Laboratory of Food Biochemistry, Graduate School of Fisheries Sciences, Hokkaido University, Hakodate 041-8611, 2Central Research Laboratory, Nippon Suisan Kaisha Ltd., Hachioji, Tokyo 192-0906, Japan
Marine fish species such as the gadoid family contain a large amount of trimethylamine-N-oxide (TMAO) which is cleaved to equimolar amounts of dimethylamine (DMA) and formaldehyde (FA) during storage. The cleavage of TMAO was investigated at subzero temperatures in a model system containing Fe2+ and reductants, ascorbate and cysteine, in the presence or absence of TMAOase which was prepared from walleye pollack muscle. At −4°C in the supercooled solution, TMAO was cleaved to DMA and FA with TMAOase depending on enzyme concentration. Almost no nonenzymic cleavage occurred practically. However, in the frozen state at −4°C as well as at −20 and −40°C, the enzymic cleavage was completely depressed and DMA was rapidly and greatly produced by the nonenzymic pathway in a Fe2+-Cys system accompanied by a little formation of trimethylamine. Both enzymic and nonenzymic reactions required only Fe2+ with reductants to maintain the reaction.