Influence of formaldehyde in the formation of fluorescence related to fish deterioration

In previous studies fluorescence detection at different excitation/emission maxima during common fish processing has been used. A bathochromic shift towards higher wavelength maxima was observed and measured as the ratio between absorption at two of the maxima tested. This fluorescence ratio (delta F) value correlates positively with fish damage. In the present work, the influence of formaldehyde (FA) on the value delta F was studied. A model system was set up in which FA reacted at 30 degrees C for 25 days with propylamine and fish muscle. It was observed that FA was less able to produce fluorescent compounds compared with common fish oxidation products that were also tested, i.e. propanal and hexanal. However, in the presence of both lipid oxidation aldehydes, the FA-containing mixtures led to a higher delta F value. Model systems consisting of FA and fatty fish (sardine) muscle produced more fluorescence than FA and lean fish (cod), because of the formation of lipid oxidation compounds under the reaction conditions of the former systems. It is thus concluded that the presence of FA in a reacting medium enhances fluorescence formation, such that delta F be can used as an accurate measure of fish damage. It is thought that measurement of delta F in processes such as the freezing of gadoid fish, in which both FA and lipid oxidation are produced, could be of benefit.