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What Causes Rigor Mortis in Poultry?

Last Updated: 05.06.20

 

Besides getting the right chicken waterer, poultry meat producers need to handle rigor mortis right, to get high-quality meat. After a bird’s death, the muscles consume the remaining adenosine triphosphate they contain as energy, before getting into rigor mortis, which usually takes between 3 and 6 hours. 

When we hear the words “rigor mortis” we know they are not related to something positive. On the other hand, poultry meat producers need to be aware of this phenomenon, given that it affects the quality of the product they are making. Rigor mortis is also known as postmortem rigidity, and it’s actually the third stage of death. 

This phase is characterized by overall body stiffness and it’s caused by changes in muscles as blood is no longer circulating within the body, which means that oxygen is not provided to all of the muscle cells. As cells and tissues die, once the animal is no longer alive either, they cannot respond to their environment, as they did beforehand. 

The process of rigor mortis is central to meat quality, and for this reason, the muscles should be considered aggregates of cells. Each of these muscle cells is undergoing a particular response to the environment and, of course, to death. Before we go into details on how this affects poultry, let’s see how the process takes place. 

 

How does the process take place? 

As animals die, the muscle cells keep on producing and consuming what is known as adenosine triphosphate, or ATP. This is the main currency when it comes to cellular energy, and as this gets depleted, cells remain solely dependent on anaerobic metabolism. 

The end product of anaerobic metabolism, namely lactic acid, accumulates given that there is no blood to move it around, which leads to stopping the production of ATP. However, its consumption continues until the first phase of rigor mortis begins. Once the ATP reaches a concentration of about 0.1 mM/g, rigor mortis is developed. 

In this phase, the muscle cannot relax, thus becoming stiff, the overall process being determined by the strength of opposing muscle groups. Temperature also plays a role in the process of rigor mortis, as this can influence how fast it develops. 

Studies have shown that birds are dead somewhere between 1.5 and 6 minutes after they are sacrificed, which means that they become unresponsive. However, muscle cells need a longer time before becoming unresponsive, which would mean the development of rigor mortis, with the average period being around 3 up to 6 hours.  

This period can also depend on the type of muscles we are talking about, given that differences were noticed between aerobic and anaerobic muscles. Research has shown that individual protein molecules, as well as aggregates, can respond to various factors within the chemical environment, namely temperature, pH, water activity, color, texture, and others. 

This means that muscles or their components never really fail to respond to the environment, which indicates that the quality of the meat can be influenced until its consumption. 

 

 

Quality control 

As you can imagine, all of these findings are important for meat producers, given that they indicate various ways in which the quality of the end product can be ensured. On the other hand, before getting into more details when it comes to poultry meat, it’s a good idea to define what the term “quality” means. 

This task might prove to be more difficult than one would expect, given that every person along the production and distribution chain can define quality in his or her own way, and considering particular characteristics. For example, someone who is trying to sell poultry meat might define the product’s quality based on how well it sells and how customers perceive it. 

Of course, there are a lot more aspects that need to be considered when it comes to this type of product, and somehow consumers are closer to the truth. Anyone who buys a poultry product and cooks it for the family, expects it to look and taste in a certain way. If these characteristics are not met, the product is not considered to be a high-quality one, which is probably true. 

While consumers determine a product’s quality based on how they perceive it, producers need to know that there are several factors that can determine its overall quality, especially in terms of texture, appearance, and flavor. In the next lines, we’re going to take a closer look to see what these are. 

 

Poultry meat color 

One of the first aspects that any consumers take into consideration, whether we’re talking about cooked or raw poultry meat, is its color. This is crucial for producers since consumers always associate it with freshness, and this can determine whether they are going to buy the product or not. 

Poultry is also a unique type of meat, given that it can be sold either with or without its skin. It’s also the only species known for its muscles that range dramatically in color, from white all the way to dark meat. Breast areas are expected to have a pale color in its raw state, while the leg and thigh ones are expected to be a darker red when raw. 

If the meat doesn’t have the expected colors, as it can sometimes happen, this poses some serious problems for producers and sellers. The aspect of color can be affected by various factors such as the bird’s diet, age, intramuscular fat, sex, meat moisture content, or on pre-slaughter conditions and other processing variables. 

The color can also depend on whether muscle pigments such as hemoglobin and myoglobin are present or not. Any discoloration that appears can be limited to a specific area if a bruise occurred for example, or it can cover the entire muscle. 

Breast muscles are known for often being subject to discolorations because they account for a significant percentage of the live weight, which is actually a lot. Moreover, their light appearance also makes any changes even more noticeable. Extreme temperatures or other aspects, such as stress that can occur due to live handling, can cause turkey breast meat to be discolored, studies show. 

 

 

Texture 

Besides the product’s color, consumers also assess its texture and tenderness as they eat it in order to determine whether they are going to buy the same brand again. When it comes to poultry meat, whether it’s tender or not depends on various factors, such as the extent and rate of the physical and chemical changes that occur when the muscle becomes meat. 

Going back to rigor mortis for a bit, it’s important to know that the muscles eventually become soft again, which means that families can enjoy their tender texture when cooked. Situations in which the process of rigor mortis or the softening process that follows it are interfered with, affect the product’s texture and tenderness. 

For example, if birds struggle in the process, their muscles run out of energy faster, which means that rigor mortis installs quicker. The resulting meat will be somewhat tougher, and the same happens if birds are exposed to various types of environmental stress, such as very hot or cold temperatures. 

The product’s tenderness can also be influenced by the timing of the deboning process. When this takes place early postmortem, the muscles still have the energy to contract, and if this happens, they become tough. Studies show that if producers wait for some time between 6 and 24 hours (also known as ‘aging time’), chances are that they are going to obtain tender meat. 

On the other hand, this means higher production costs, so the poultry industry has come up with solutions to meet both the needs of the producers and those of consumers in terms of quality. Electrical stimulation has been a good answer to this issue, and if this is done immediately after death, it hastens the entire process by reducing the ‘aging’ time necessary before deboning. 

This solution works because, as opposed to the energy depletion of the live bird that causes the meat to get tough, electricity acts like a nerve impulse, which means that muscles contract, use up their energy and get into the rigor mortis phase at a faster rate. 

While muscle energy depletion in live birds makes the meat tougher, when this is done after death, the result is quite the opposite. The deboned poultry is ready within 2 hours postmortem, which is much quicker than the 4 to 6 hours needed in the normal aging process. 

 

 

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