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.