Comparison of oxidation extent, structural characteristics, and oxidation sites of myofibrillar protein affected by hydroxyl radicals and lipid-oxidizing system

To compare the differences between direct protein oxidation (PO) and lipid-derived PO, the myofibrillar protein (MP) of obscure pufferfish was oxidatively modified by the hydroxyl radical oxidizing system (HOS) and the lipid-oxidizing system (LOS). The degree of oxidation, structural characteristics, and oxidation sites in MP were assessed. The results showed there was no significant thiol loss in LOS, compared with a 77.64% loss observed in case of the HOS. The secondary structure of MP was more vulnerable to HOS, but the tertiary structure was more susceptible to LOS. The cross-linking was largely attributed to the reversible disulfide links in HOS and the irreversible covalent linkages in LOS. Six amino acids and 10 specific oxidant products were identified in HOS. Only three amino acids and three specific oxidant products were identified in LOS. These findings may help deepen the understanding regarding the mechanism underlying PO in protein- and lipid-rich food materials.