INFLUENCE OF LIPIDS ON DIMETHYLAMINE FORMATION IN MODEL SYSTEMS OF HAKE (MERLUCCIUS-MERLUCCIUS) KIDNEY DURING FROZEN STORAGE

The role of non-oxidized and oxidized lipids in fish muscle proteins d uring frozen storage is a matter of controversy: some studies have sho wn that they have a detrimental effect, whereas others have shown a pr otective effect through a reduction in the amount of formaldehyde (FA) and dimethylamine (DMA) formed from trimethylamine N-oxide (TMAO) dur ing frozen storage. A model system based on an extract of hake kidney as a source of trimethylamine N-oxide demethylase (TMAO-ase) and the s ubstrate TMAO was prepared to study the effects of nonoxidized lipids and oxidized lipids with increasing peroxide values (POV) and of a cry oprotectant (glycerol) on TMAO-ase activity during frozen storage, usi ng response surface methodology (RSM). At low POV, the oxidized lipids increased DMA formation, but at oxidation levels equal to or higher t han 500 meq kg(-1) they reduced the amount of DMA produced. This behav iour corroborates the hypothesis that oxidizing/reducing conditions st rongly 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 .