Abstract
The role of non-oxidized and oxidized lipids in fish muscle proteins during frozen storage is a matter of controversy: some studies have shown that they have a detrimental effect, whereas others have shown a protective effect through a reduction in the amount of formaldehyde (FA) and dimethylamine (DMA) formed from trimethylamine N-oxide (TMAO) during frozen storage. A model system based on an extract of hake kidney as a source of trimethylamine N-oxide demethylase (TMAO-ase) and the substrate TMAO was prepared to study the effects of non-oxidized lipids and oxidized lipids with increasing peroxide values (POV) and of a cryoprotectant (glycerol) on TMAO-ase activity during frozen storage, using response surface methodology (RSM). At low POV, the oxidized lipids increased DMA formation, but at oxidation levels equal to or higher than 500 meq kg–1 they reduced the amount of DMA produced. This behaviour corroborates the hypothesis that oxidizing/reducing conditions strongly influence the capacity of the enzyme to catalyse the reaction. However, non-oxidized lipids were found to have a very weak inhibitory effect. Glycerol had a significant inhibitory effect on DMA formation, greater than that of oxidized lipids in the present enzymatic system.
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