The objective of this study was to investigate the effect of chemical oxidation on proteolysis susceptibility of myofibrillar proteins. Myofibrils were prepared from pig M. longissimus dorsi and oxidised by a hydroxyl radical generating system. Protein oxidation level was measured by the carbonyl content, free thiol group content and bityrosine formation. Oxidised or non-oxidised myofibrillar proteins were exposed to papain and proteolysis was estimated by fluorescence using fluorescamine. Oxidation of myofibrillar proteins was dependent upon the oxidising agent concentration. Disulfide bridge and bityrosine formation indicated that oxidation by OH° can induce protein polymerization. Electrophoretic study showed that myosin was the protein most sensitive to oxidation. Results showed a direct and quantitative relationship between protein damages by hydroxyl radical and decreased proteolytic susceptibility. Electrophoretic observations suggest that polymerization and aggregation may explain in part decreased susceptibility of myofibrillar proteins to proteolysis.

The aim of this work was to compare the oxidative processes occurring in myofibrillar proteins during meat maturation and after an in vitro exposure to different enzymic and nonenzymic oxidative systems. Myofibrils were prepared from bovine Longissimus lumborum and Diaphragma pedialis at day 1 and day 10 post-mortem. Myofibrillar protein oxidation was measured by the carbonyl content, with the 2,4-dinitrophenylhydrazine (DNPH) method, and by (thiol group) SH content with the 2,2‘-dithiobis(5-nitropyridine) (DTNP) method. Polymerization and/or fragmentation of oxidized proteins were estimated by SDS-PAGE and Western blot analysis using a polyclonal antibody to myosin. Oxidation of myofibrillar proteins is dependent upon the different metal-catalyzed oxidation (MCO) systems. The increase in carbonyl content and also the decrease in SH content of myofibrillar proteins, after maturation of 10 days, were similar to those obtained after a 1 h incubation of myofibrillar proteins in the presence of several MCO systems. Electrophoretic studies showed that myosin was the protein the most sensitive to oxidation, and to a lesser extent, troponin T. Myosin-oxidative products were also detected by Western blot analysis. Keywords: Beef; myofibrillar proteins; protein oxidation; carbonyl content; SH-content; metal-ion catalyzed oxidation system; SDS−PAGE; Western blotting

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