Protein Thiols Undergo Reversible and Irreversible Oxidation during Chill Storage of Ground Beef as Detected by 4,4′-Dithiodipyridine

Quantification of protein thiols and disulfides in ground beef during storage under high-oxygen atmosphere at 4 °C was performed by thiol detection using 4,4′-dithiodipyridine (4-DPS) before and after disulfide reduction using sodium borohydride. Two independent storage trials were performed, and in trial 1, only reversible thiol oxidation was observed (thiol loss was 30%). In trial 2, irreversible thiol oxidation occurred during the first days of storage, while further loss of thiols was caused by reversible disulfide formation (thiol loss was 33%, of which ca. half was lost because of irreversible oxidation). The results were compared to sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE) analysis of cross-linked myosin heavy chain formed by disulfide bonding. Both methods confirmed increasing disulfide formation because of thiol oxidation in meat during storage, but the 4-DPS method showed higher disulfide percentages than the SDS–PAGE method (22.2 ± 0.3% and 8.5 ± 1.2%, respectively). The 4-DPS assay provides an accurate method to evaluate the thiol–disulfide redox state in meat.