Concentration effects of hydroxyl radical oxidizing systems on biochemical properties of porcine muscle myofibrillar protein

The objective of the study was to determine the dose-dependency of myofibrillar protein oxidation on oxidizing ferric ion. Pork myofibrillar protein isolates (MPI) were suspended in 15 mM piperazine-N,N bis(2-ethane sulfonic acid) (PIPES) buffer (pH 6.0) with 0.6 M NaCl, and incubated at 4 °C for 24 h with two levels of ferric ion (0.01 and 0.1 mM FeCl3) at eight concentrations of hydrogen peroxide (0.00–10 mM H2O2). In both high and low [FeCl3] oxidizing systems, the Ca-ATPase activity steadily increased with the H2O2 concentration. On the other hand, K-ATPase activity, protein carbonyl content, and 2-thiobarbituric acid-reactive substances increased with H2O2 up to 1.0 mM, and then gradually declined. Protein unfolding and loss of myosin heavy chain occurred continuously with increasing H2O2 concentrations. All changes, except for K-ATPase activity, were generally more rapid and extensive in the high [FeCl3] oxidizing system. Overall, the biochemical changes in MPI exposed to ferric iron-oxidizing systems were more pronounced at high [FeCl3] than at low [FeCl3], but the pattern of the biochemical alterations appeared to be independent of the FeCl3 concentration.