Variation in the cross-linking pattern of porcine myofibrillar protein exposed to three oxidative environments

Myofibrillar protein (MP, 26 mg protein/mL in 0.6 M NaCl, pH 6.0) prepared from pork serratus ventralis muscle was incubated at 4°C for 24 h with three oxidizing systems: (1) an iron-catalyzed oxidizing system (IOS: 10 μM FeCl₃, 0.1 mM ascorbic acid, and 0.05-5.0 mM H₂O ₂), (2) a linoleic acid-oxidizing system (LOS: 0.05-5.0 mM linoleic acid and 3750 units of lipoxidase/mL), or (3) a H₂O ₂-activated metmyoglobin-oxidizing system (MOS: 0.05-0.5 mM metmyoglobin/ H₂O₂). Oxidation in IOS and MOS promoted extensive, dose-dependent cross-linking and insolublization of MP, notably myosin, while the effect of LOS was minimal. Chymotrypsin digestion indicated that the rod (tail) subfragment of myosin was the preferred target of hydroxyl radicals and ferryl oxygen species, although the s-1 (head) region was also susceptible. Disulfide bonds were responsible for most of the cross-linking, and malonaldehyde appeared to contribute to the cross-linking as well. However, dityrosine was minimally involved. Overall, the systems that generate hydroxyl radicals and ferryl oxygen species were more potent than the system that produces peroxide in the cross-linking and aggregation of MP; such covalent links were implicated in the functionality changes of low-temperature-processed muscle foods.