Addition of partly reduced bovine serum albumin to a metmyoglobin-fortified washed cod system gives reduced formation of lipid oxidation products and increased degradation of proteins

The aim of the investigation was to study the pro-oxidative system of washed cod with added horse metmyoglobin (metMb) regarding lipid and enzyme oxidation plus protein degradation. The changes were studied at pH 5.6 and 2 °C for 47 h. Bovine serum albumin (BSA) with 0.2 or 3.5 thiol (reduced) groups per molecule was added as an antioxidant protein and as providers of free thiols. BSA with the higher amount of thiols decreased the formation of lipid peroxides and thiobarbituric acid reactive substances (TBARS) in the washed cod system. Metmyoglobin (metMb) addition slowed down the enzymatic release of proteins and protein fragments from insoluble washed cod proteins while the opposite was observed with added reduced BSA. Addition of metMb strongly inactivated the thiol proteases cathepsin B + L and effectively oxidized the low molecular weight thiols in the system while reduced BSA slowed down inactivation of the proteases. The endogenous proteases degraded BSA to a fragment of 41.7 kDa. Formation of this fragment was reduced when metMb was added. BSA (not reduced) did not influence TBARS formation in the washed cod system with metMb, but increased the formation of lipid peroxides after 47 h compared to the system without BSA.