OXIDATIVE STABILITY OF FRESH AND HEAT‐PROCESSED DARK AND LIGHT MUSCLES OF MACKEREL (Scomber scombrus)

Oxidative stability of light and dark comminuted muscle of raw and thermally processed mackerel stored at 4C was studied over a 21 day period by monitoring changes in conjugated dienes (CD) and 2-thiobarbituric acid (TBA) values. The quantity of headspace (HS) volatiles, propanal, and hexanal as well as the ratio of aliphatic to olefinic (Rao) or diallylmethylene (Rad) protons in the proton nuclear magnetic resonance (1 NMR) spectra of oils were determined. The content of CD of light and dark ground mackerel muscle samples exhibited a consistent increase over the entire storage period. Furthermore, secondary oxidation products as reflected in the TBA values and content of propanal, hexanal and HS gases, generally, showed a gradual increase in their level. The concentration of propanal, the dominant volatile of the HS gases, increased markedly up to day 6 of storage, but afterwards began to decline continuously. A similar trend was noted for hexanal, but at a lesser extent. The Rao and Rad values in the 1H NMR spectra of lipids from all stored samples increased constantly during storage. In all samples, the dark ground muscle exhibited a higher degree of oxidation than its light counterpart. Furthermore, heat-processed dark comminuted muscle oxidized faster than its raw counterpart while generally an opposite trend was observed for the light ground muscle.