Factors affecting solubilisation and oxidation of proteins during equine metmyoglobin-mediated lipid oxidation in extensively washed cod muscle

Lipid and protein changes in extensively washed cod muscle were studied at pH 5.6 and 2 °C for 47 h in the absence and presence of horse metmyoglobin (metMb). MetMb significantly increased lipid peroxides and TBARS formation. MetMb addition reduced solubility of proteins, such as myosin heavy chain and its fragments, and slowed down the enzymatic release of soluble proteins and protein fragments, e.g. fragments from collagen.Changes in thiols were monitored during storage as an indicator of protein oxidation. Added metMb reduced the number of soluble thiols as observed after 1.5 h using fluorescent labelling of formed disulfides and at later times for both soluble and insoluble proteins when determined by colorimetric measurements. Loss in the activity of the thiol-dependent proteases cathepsin L + B was observed with metMb addition. MetMb also became less soluble during the incubation period and a small amount of metMb was degraded by the still remaining protease activity.