The effects of an iron-catalyzed oxidation system on lipids and proteins of dark muscle fish

The effects of a hydroxyl radical-generating system induced by iron catalyzed oxidation (Fe2+/H2O2) on lipids and proteins of sardine, Atlantic bonito, anchovy and bluefish were investigated. Thiobarbituric acid-reactive substances (TBARs, mg malonaldehyde/kg fish muscle) formation was used to evaluate oxidative damage of the lipid in dark muscle fish due to iron catalyzed oxidation. The amount of TBARs was observed to increase significantly in sardine and anchovy as the incubation time increased, while Atlantic bonito and bluefish reached their maximum values of TBARs within the first 3 h of incubation, and after that did not change (p < 0.05). Carbonyl contents (nmol carbonyl/mg protein) of all fish samples measured as an index of protein oxidation were affected differently by the iron-catalyzed oxidation system during incubation. However, significant increases in the carbonyl groups were detected in sardine, Atlantic bonito and bluefish, but not in anchovy as a result of the long incubation time (5 h) (p < 0.05). When comparing to increases Atlantic bonito showed the maximum increase protein carbonyl. The electrophoretic patterns in the presence and absence of β-mercaptoethanol showed that a loss of proteins generally occurred in all fish at the end of incubation, and the greatest alteration in protein bands was observed in anchovy during Fe2+-catalyzed oxidation. The bands above 50 kDa disappeared within the first 1 h of incubation. The loss of protein (both high and low molecular weight) may involve disulfide and non-disulfide covalent linking during the iron catalyzed incubation. These data suggest that an increase in TBARs and fragmentation, and a loss of proteins exposed to iron-catalyzed oxidation may explain the oxidative damage of lipids and proteins which causes quality loss and limits the storage life of dark muscle fish.