Relevance of trimethylamine oxide demethylase activity and haemoglobin content to formaldehyde production and texture deterioration in frozen stored minced fish muscle

Minces were prepared from white muscle or fillets of gadoid and non‐gadoid fish species. After the addition of blood, kidney or formaldehyde the minces were stored frozen for 6 months at −8 and −30°C. Blood and kidney of the gadoid species contained trimethylamine oxide demethylase (TMAOase), whereas in the tissues of the other species no activity of this enzyme could be detected. The formation of dimethylamine (and formaldehyde) was correlated with the TMAOase activity of the added tissues. The concentration of haemoglobin in the minces had no influence on the dimethylamine and formaldehyde production during frozen storage. The formaldehyde production was accompanied by an increase in the firmness of the texture as measured by mechanical and sensory tests.