This is an accepted article with a DOI pre-assigned that is not yet published.Post-translational modifications (PTMs) of proteins play critical roles in biological processes. PTMs of muscle proteins influence meat quality. Nonetheless, myoglobin (Mb) PTMs and their impact on fresh beef color stability have not been characterized yet. Therefore, our objectives were to identify Mb PTMs in beef longissimus lumborum (LL) muscle during postmortem aging and to characterize their influence on color stability. The LL muscles from nine (n = 9) beef carcasses (24 h postmortem) were subjected to wet-aging for 0, 7, 14 and 21 d. At the end of each wet-aging period, steaks were fabricated. One steak for analyses of PTMs was immediately frozen at –80°C, whereas other steaks were assigned to refrigerated storage in the darkness under aerobic packaging. Instrumental color and biochemical attributes were evaluated on d 0, 3, or 6 of storage. Mb PTMs were analyzed using two-dimensional electrophoresis and tandem mass spectrometry. Surface redness (a* value), R630/580 (color stability), and Mb concentration decreased (P < 0.05) upon aging. Gel image analyses identified six Mb spots with similar molecular weight (17 kDa) but different isoelectric pH. Tandem mass spectrometry identified multiple PTMs (phosphorylation, methylation, carboxymethylation, acetylation, and HNE alkylation) in these six isoforms. The amino acids susceptible to phosphorylation were serine (S), threonine (T), and tyrosine, whereas other PTMs are detected in lysine (K), arginine (R), and histidine residues. Additionally, distal histidine (position 64), critical to heme stability, was found to be alkylated. Overall, Mb PTMs increased with aging. The aging-induced PTMs, especially those occurring close to hydrophobic heme pocket, could disrupt Mb tertiary structure, influence heme affinity, and compromise oxygen binding capacity, leading to decreased color stability of fresh beef. Furthermore, PTMs at K45, K47, and K87 were unique to Mb from non-aged beef, whereas PTMs at R31, T51, K96, K98, S121, R139, and K147 were unique to Mb from aged counterparts, indicating these Mb PTMs could be used as novel biomarkers for fresh beef color stability.
Keywords: post-translational modifications, myoglobin, longissimus lumborum, beef color stability, aging