Effect of pH on fluorescence formation related to fish deterioration

Abstract

Earlier studies have investigated fluorescence at different excitation/emission maxima during common types of fish processing. A shift towards higher wavelength maxima was observed and measured as the ratio between two of the maxima tested. This fluorescence ratio (δF) correlated with increased fish damage. The present work is focused on the effect that pH can have on the formation of fluorescent compounds in fish muscle systems. Minced hake muscle was homogenised with 0.1 M phosphate buffer of different pH values (5, 6, 7 and 8) and was stored at 30 °C for up to 30 days. Lipid damage, measured as the δF value of the aqueous reaction medium and the fish lipid extract, indicated little difference between the effect of different pH values under the conditions employed in the present experiment. The effetct of formaldehyde (FA) in the same reaction medium was also evaluated. It was observed that FA had a positive effect on the fluorescence shift occurring in the aqueous reaction medium, so that a higher δF value was observed for pH 7 and pH 8, especially for the latter. It is concluded that changes in the δF value during fish storage and/or processing are of special interest as, in addition to FA formation and lipid oxidation, significant pH increases are expected to occur as a result of damage.