Proteomic study on structural characteristics of wheat germ protein induced by lipid rancidity during storage

This project aimed to investigate the effect of lipid rancidity of wheat germ during storage on oxidation of wheat germ protein (WGP). Wheat germ was stored at 25 °C under 70 % relative humidity for 2, 4, 10, and 16 days. Oxidative and structural changes in WGP were subsequently characterized. The types and sites of oxidative modifications in WGP were analyzed using LC-MS/MS-based proteomics. Results showed that fatty acid value gradually increased during storage. Carbonyl content increased from 2.31 ± 0.14 to 16.96 ± 0.43 nmol/mg prot during storage. After 16 days of storage, free sulfhydryl content decreased by 53 %, and total sulfhydryl content by 29.4 %. Disulfide bonds increased by 43.66 %, and di-tyrosine by 170.39 %. These data indicate that WGP oxidation occurred concomitantly with lipid oxidation. Oxidation induced changes in surface hydrophobicity, tertiary structure, and secondary structure, accompanied by protein aggregation. Amino acid composition was altered after oxidation, with nearly all amino acids showing reduced levels. Tyr, Pro, His, and Lys exhibited the most significant losses, decreasing by 24.95 %, 20.14 %, 18.64 %, and 18.42 %, respectively, after 16 days of storage. The proteomic results showed that the amount of oxidized peptide increased from 174 in the fresh sample to 353 in the samples stored for 16 days. Primary modification types included oxidation, 4-hydroxy-2-nonenal adduction, and carbonylation. This study elucidates the oxidation mechanism of WGP induced by lipid oxidation during storage and provides a scientific basis for precise control of WGP oxidation.