In addition to naturally occurring formaldehyde in foods,
formaldehyde is added into some food products as a preservative
[9]. European Commission Directive 95/2/EC allows
formaldehyde in provolone cheese at a residual concentration
of 25 mg/kg [10]. In 2006, the European Food Safety Authority
concluded that formaldehyde is not carcinogenic by the oral
route [11]. European Commission Directive 2009/10/EC allows
a maximum level of formaldehyde residues of 50 mg/kg in
gelling additives [12]. With the exception of its use as food
additives, the therapeutic use of formalin in the aquaculture
industry is approved in both the US and Canada [13]. However,
Australia, Europe and Japan have not approved formaldehyde
as an aquatic chemotherapeutant because of its association
with oncogenesis. Although formaldehyde occurs endogenously
in fish, Bianchi et al pointed out that in 1985, the Italian
Ministry of Health proposed standard maximum limits of
60 mg/kg for Gadidae and 10 mg/kg for crustaceans [14].
As formaldehyde is sometimes used illegally as a food
preservative in aquatic products, many countries have
investigated the form and content of formaldehyde in seafood
products for the sake of food safety regulations [14e19].
Nielsen and Jørgensen found that trimethylamine oxide
aldolase could break down trimethylamine N-oxide (TMAO)
into formaldehyde and dimethylamine even at freezing temperatures
[20]. Formaldehyde can react with a number of
amino acid residues in proteins, resulting in protein denaturation
and cross-linking. Formaldehyde-deteriorated
aquatic products are characterized as tough, hard, fibrous and
dry.