Dark-cutting beef mitochondrial proteomic signatures reveal increased biogenesis proteins and bioenergetics capabilities.

Mitochondria remain active in postmortem muscles and can influence meat color via oxygen consumption. Previous studies have shown that dark-cutting compared with normal-pH beef has greater mitochondrial protein and DNA content per gram of muscle tissue. However, the mechanism regulating mitochondrial content in dark-cutting vs. normal-pH beef is still unknown. Therefore, the objective was to compare mitochondrial proteomes of dark-cutting vs. normal-pH beef using LC-MS/MS-based proteomics and mitochondrial respiratory capacity using a Clark oxygen electrode. Dark-cutting compared with normal-pH beef has up-regulation of proteins involved in mitochondrial biogenesis, oxidative phosphorylation, intracellular protein transport, and cellular calcium ion homeostasis. Mitochondria isolated from dark-cutting phenotypes showed greater mitochondrial complex II respiration and uncoupled oxidative phosphorylation. However, mitochondrial membrane integrity and respiration at complexes I and IV were not different between normal-pH and dark-cutting beef. These results indicate that dark-cutting beef has greater mitochondrial biogenesis proteins than normal-pH beef, increasing mitochondrial content and contributing to dark-cutting beef. SIGNIFICANCE: Defective glycogen metabolism resulting from chronic stress before slaughter coupled with the greater mitochondrial protein and DNA content per gram of muscle tissue promotes muscle darkening in dark-cutting phenotypes in beef. However, the mechanistic basis for this occurrence in dark-cutting phenotypes is still unknown. In this work, we show that dark-cutting beef phenotype is caused, in part, as a consequence of over-proliferation of mitochondria. This is supported by the up-regulation of proteins involved in mitochondrial biogenesis, mitochondrial electron transport, calcium homeostasis, and fatty acid metabolism. Hence, the study of mitochondrial proteome changes provides a set of mitochondrial biogenesis proteins that could be used as potential candidate markers for detecting changes in pre-slaughter developmental events contributing to dark-cutting phenotypes in beef.