Pork longissimus muscle samples were subjected to the following three marination conditions: (A) oxidation (40 min) in hydroxyl radical-generating solutions (HRGS; 10 μM FeCl(3)/100 μM ascorbate with 5 or 20 mM H(2)O(2), pH 6.2) containing 0.1 M NaCl and then marination (40 min) in 0.6 M NaCl with 15 mM pyrophosphate (PP); (B) simultaneous oxidation/marination (40 min) in HRGS containing 0.6 M NaCl and 15 mM PP; or (C) the same as condition B except that PP was omitted. Protein oxidation, measured by the carbonyl and tryptophan fluorescence changes, enhanced hydration but increased cooking loss of meat. Light microscopy revealed a dense muscle structure characterized by swollen fibers and reduced intercellular spacing in intermediately oxidized muscle samples marinated with 0.6 M NaCl and 15 mM PP. However, oxidized fibers were more susceptible to transverse shrinkage upon cooking than nonoxidized fibers, which was supported by the dynamic ultrastructural changes in myofibrils observed using phase contrast microscopy. These findings provide a further understanding of the complex impact of oxidation on meat hydration and water-binding.