Application of proteomics in mechanism research of fresh meat color changes

Abstract: Meat color is a major quality attribute that influences the purchasing decisions of consumers at the point of sale. The stability of meat color gradually decreases after slaughter which then eventually leads to the discoloration. The discoloration will result in lost value during retail display. So, the mechanism behind slaughtering meat color variation is always a hot topic in the field of meat science which has been widely studied in order to improve meat color stability. Many factors from both preharvest and postharvest can influence the color stability, including pH value, temperature, different muscle, package, lipid oxidation, processing and so on. However, in this complex system, the inherent factors that determine meat color include the microstructure changes and biochemical functions. The structural protein determines the micro spatial structure of muscle, which affects the meat color from the aspects of water holding capacity, light scattering, and projection, etc. Enzymes and chaperones in sarcoplasmic protein mainly represent meat color by maintaining intracellular homeostasis, and regulate metabolism and myoglobin status. So far, the effects of many factors on meat color have been described in detail, and the role of myoglobin in meat color has been much clear. However, the appearance of meat color is a complex biochemical system, and there are still many unknowns to be explored. What happens to myoglobin and other functional proteins in this complex system remains unknown. Recently, many protein markers have been found in the application of proteomics in meat color research, and the pathways related to these biomarkers have been highlighted. However, that is still far from enough to clearly understand the variable color changes. The complex interaction between myoglobin and other functional proteins or enzymes are not fully understood. Therefore, the present article reviews the major achievements of recent proteomic researches on meat color of the biological functions and further summarized the potential mechanism of fresh meat discoloration. The differential proteins related to meat color were mainly analyzed. These differential proteins mainly include actin, myosin and titin in structural proteins, as well as chaperone proteins, heat shock proteins, metabolic enzymes and oxidoreductases in sarcoplasmic proteins. Effects of these proteins on meat color and its possible regulatory mechanisms were analyzed. The effects of structural protein abundance differences on light transmittance, absorption and scattering are reviewed from a physical point, and finally lead to the color changes. The difference proteins in sarcoplasmic proteins were reviewed from the perspective of biochemistry. Chaperones can maintain the stability of protein and slow down the denaturation of protein, thus helping to maintain the stability of meat color. Metabolic enzymes mainly affect a* value and metmyoglobin reductase activity. But due to different treatments in previous studies, the results of some metabolic enzymes have not reached a consistent conclusion. Further work still needs to be done to get the final conclusion. Oxidoreductases can maintain the stability of redox state in cells, and then benefit to maintain the color stability. Peroxidase can inhibit lipid oxidation and then help maintain color stability. It suggests that in future, protein biomarkers may be used to explain and predict meat color development. In this research, the mechanism of meat color improvement and the regulation of biomarkers were proposed.