DENATURATION OF FISH PROTEINS DURING FROZEN STORAGE - ROLE OF FORMALDEHYDE

Proteins of fish muscle undergo chemical and physical changes during f rozen storage which may result in, under certain conditions (i. e. lon g periods of storage, poor freezing practices, temperature fluctuation s, etc), loss of quality, reflected mainly by an unacceptable texture as well as an undesirable flavour, odour and colour. In frozen gadoid fish species, most of these changes are caused by the production of fo rmaldehyde in the muscle. Formaldehyde is produced, along with dimethy lamine, by the enzymatic reduction of trimethylamine oxide (TMAO). Man y aspects of formaldehyde production by TMAO demethylase (TMAOase) hav e been studied throughout the last decade. In addition, different appr oaches have been used to investigate the effect of formaldehyde produc tion on protein denaturation and the associated muscle textural change s. Some insight into the reaction between protein and formaldehyde has clarified the possible mechanism of formaldehyde-mediated denaturatio n. However, evidence of covalent bonding between proteins and formalde hyde, to form crosslinks, has not explained fully the changes observed in fish proteins during frozen storage. The study of cold-induced den aturation of proteins might give new clues for further investigation o f the problem. The implications of formaldehyde in toxicological and n utritional issues is also reviewed, as general concern about the safet y of food products is a growing field in food science. Finally, differ ent approaches have been proposed to avoid the detrimental action of f ormaldehyde during frozen storage of gadoid fish; they art: some of th e practical applications of the knowledge acquired after years of stud y of different workers in the field.