Summary written and edited by New Harvest Journal Club’s Christian Gainsley and Francis Runge, respectively.
Abstract: Cellular death is characterized by a complex pattern of molecular events that depend on cell type. Specifically, muscle cells first undergo rigor mortis due to ATP depletion, and later, on the time scale of days, muscle fiber degradation due to proteolytic enzyme activity. In the present review, we will refer to proteomic investigations on the post-mortem evolution of the protein patterns of animal muscle cells. These studies, carried out with the application of either bottom-up or top-down methods, are relevant for understanding the biochemical reactions that i) convert muscle to meat, ii) are associated with meat aging and iii) impact on meat tenderness, a feature of significant commercial value. We also report on the proteomic investigations that have been made to analyze the transformation of meat in industrial processes. These studies are primarily aimed at identifying protein patterns and/or individual proteins diagnostic of the quality of the final product. This article is part of a Special Issue entitled: Farm animal proteomics.
Overview: To better understand the cellular conversion of muscle from living tissue to edible meat product, the authors of this article surveyed existing research of proteomic analyses of different animal muscle after death and through various cooking methods. The proteomic analyses themselves are also an important focus of the article. Proteomics is the study of proteins and their effects in a cell.In the article, the authors examine not just the specific proteins or protein patterns identified in prior published examinations of animal post-mortem muscle, but also the types of analysis used, whether or not sufficient examination of the animals was carried out, and at correlations between the results of the studies.
Proteomic analysis is being used in some cases to help the meat industry better understand what constitutes good quality meat prior to slaughter (cell health, fat deposition). It is also being used to look at things like:
- Determining how different biological traits may influence outcome.
- Determining what disease(s) affect meat quality.
- Determining what the effects are from handling, transport, and slaughter.
- Determining how best to track the biochemical changes of muscle post-mortem; what makes for good quality meat (water retention, appearance, tenderness).
Biochemical changes include changes that occur as a result of cell death, changes that occur over time, as meat is ‘aged’, and changes that occur as muscle is processed through industrial means (cooking or preserving).
The authors also make mention of how proteomic analysis can be used to aid consumers by helping them pick out better quality meat and/or recognize fraud (mislabeled meat).
The two main proteomic analysis results came from the tissues of cattle and pork. This reason for this is because both have undergone more testing and are a larger part of the meat market in general.
The authors also surveyed proteomic analysis results of chicken, turkey, goat, sheep, and other less commonly slaughtered animals.
In conclusion, the authors find that among the animals that make up a substantial part of the global food chain (such as beef, chicken or pork), more testing has yet to been done. They state it would be difficult to draw any thorough enough conclusions for comparative analysis. It is recommended that researchers put further focus on testing breeds and species within larger herds.
Glossary:
Biomarkers – Particular proteins or protein patterns whose quantity changes after a certain change has occurred in the muscle (could be negative effects of stress, positive effects on tenderness, fat deposition, color, etc.).
2-DE – Two-dimensional gel electrophoresis, is a common method of analyzing proteins.
PSE – Pale, soft, exudative meat. A condition known to occur in the carcass of both pork and poultry. It is characterized by an abnormal color, consistency, and water holding capacity, making the meat dry and unattractive to consumers. The condition is believed to be caused by abnormal muscle metabolism following slaughter. This is, due to an altered rate of glycolysis and a low pH within the muscle fibers. Genetic predispositions and stress levels prior to slaughter are known to affect the incidence of PSE meat.
Drip Loss – Fresh meat from slaughtered animals contains about 70% water, which is essential to its quality. This water however, begins to leak away soon after death. Boning and cutting can result in losses of 1-2%. Further long-term storage can lead to much greater losses of up to 12%. Drip loss on this scale represents a large reduction in the yield of meat, leading to financial losses as well as affecting the appearance, nutritional value and palatability of the meat to the consumer.
