Insight into the molecular mechanism underlying the enhancement of antioxidant activity in ovalbumin by high-energy electron beam irradiation

The effects of high-energy electron beam irradiation (HE-EBI) at various doses (0, 25, 50, 75, and 100 kGy) on the antioxidant activity of ovalbumin (OVA) were studied, and the molecular mechanism was investigated. The results showed that the antioxidant activity of HE-EBI-treated OVA was significantly enhanced in a dose-dependent manner. The irradiated OVA structure gradually unfolded to form a "honeycomb" structure, exposing the buried hydrophobic and free sulfhydryl groups inside the molecule. Two oxidation sites (M35 and T170), adjacent to the antioxidant peptide were identified by mass spectrometry, possibly exposing the antioxidant peptide through structural deconvolution. In addition, aspartic residues generated dicarbonyl compound under high-energy electron beam stress, and its accumulation further enhanced the antioxidant activity. Conclusively, HE-EBI can enhance the antioxidant activity of OVA through ionization effects, providing valuable information for the potential application of HE-EBI in the food industry.

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.

Proteomic profiling and oxidation site analysis of gaseous ozone oxidized myosin from silver carp (Hypophthalmichthys molitrix) with different oxidation degrees

Ozone is used to in surimi production and affects the conformation of myosin and gelling properties. Amino acid analysis, SDS-PAGE, in-gel trypsin hydrolysis and LC-MS/MS were used to investigate the effect of the ozone treatment time on the oxidation principle of amino acids to identify the oxidation site and oxidation mechanism of myosin with different oxidation degrees. The results showed that the order of ozonation of amino acids from easy to difficult was tyrosine > cysteine > histidine > proline. The protein structure near the SH1-SH2 region initially changed when the ozone treatment time was 50 s. Prolonging the oxidation to 80 s leads to an irregular distribution of oxidation sites. Ten min of ozone treatment resulted in the aggregation from the SH1 helical region and myosin rod. This study helped to clarify the mechanism of ozone oxidation, thus providing a theoretical basis for producing surimi products of improved quality.

Investigation of the effect of oxidation on the structure of β-lactoglobulin by high resolution mass spectrometry

In this work, high-resolution mass spectrometry was used to identify the oxidation sites and forms of β-lactoglobulin (β-Lg) induced by hydrogen peroxide with 1.5% concentration, and the influence of oxidation sites on the structure of β-Lg was discussed from the molecular level. Twelve kinds of oxidation products and 36 oxidation sites were identified, including sulfoxidation in sulfur-containing amino acid residue, hydroxylation in aromatic group residue, deamination in amino-containing amino acid etc. The destruction of hydrogen bonds and disulfide bonds in β-Lg caused by oxidation is the main factor causing its structural changes, which were manifested in the decrease of β-sheet component and increase of β-turns and random coil contents, intrinsic fluorescence intensity and surface hydrophobicity. In addition, several peptides as potential oxidative markers were found to be capable of monitoring the degree of oxidation of β-Lg. In short, this work provided insights into structural changes of β-Lg by oxidation.