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The colour of chicken muscle varies depending on the type of muscle and the activity level of the chicken. Chicken breast meat is typically white, while thigh meat is darker. This is because chicken breast muscles are not used as actively as thigh muscles and lack myoglobin, a protein that facilitates oxygen transport from the blood. When cooked, myoglobin turns into metmyoglobin, giving dark meat its colour. In addition, the amount and type of activity can affect the colour of chicken muscle, with endurance birds like wild geese having darker breast meat than birds that fly in short bursts.
| Characteristics | Values |
|---|---|
| Muscle Type | Slow oxidative muscle fibres (dark meat), fast glycolytic muscle fibres (white meat) |
| Muscle Location | Legs, thighs (dark meat), breast (white meat), wings (white meat) |
| Protein Content | Higher in indigenous chicken muscles than broiler muscles |
| Fat Content | Lower in indigenous chicken muscles than broiler muscles |
| Ash Content | Lower in indigenous chicken muscles than broiler muscles |
| Amino Acid Profile | Similar between indigenous and broiler muscles, except for slightly higher glutamic acid in indigenous muscles |
| Fatty Acid Content | Higher saturated and lower polyunsaturated fatty acids in indigenous chicken muscles than broiler muscles |
| Collagen Content | Higher total collagen in indigenous chicken muscles, lower soluble collagen |
| Lightness, Redness, and Yellowness | Higher CIE system values for indigenous chicken muscles |
| Shear Values | Higher for indigenous chicken muscles, especially after cooking |
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What You'll Learn
Chicken muscle colour depends on the type of muscle fibre
The colour of chicken muscle depends on the type of muscle fibre. Chicken muscle colour varies from white to dark, and this is determined by the different kinds of muscle fibres present.
Dark meat is a result of the predominant presence of slow oxidative muscle fibres, which are used for sustained activity by active muscles such as those found in the legs and thighs. These muscle fibres have a continuous rich supply of oxygen and generate low levels of force over long periods of time. They contain high levels of a protein called myoglobin that helps facilitate oxygen transport from the blood. Myoglobin is an iron-rich, red-pigmented protein that, when cooked, turns into metmyoglobin, giving dark meat its colour.
By contrast, fast glycolytic muscle fibres are mainly found in chicken breast and other muscle regions that are not used actively. These muscle fibres lack myoglobin but are capable of generating a large force over a short time span.
In some cases, a single chicken muscle can be composed of different types of muscle fibres. For example, the breast muscle primarily comprises glycolytic fibres, whereas the leg muscle comprises glycolytic and a few oxidative fibres, regardless of the breed.
The colour of chicken muscle is not a useful indicator of the presence of slow or fast muscle fibres. For instance, the tonic adductor profundus, a type of slow muscle, is white rather than red.
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Dark meat comes from slow oxidative muscle fibres
The colour of chicken muscle varies depending on the type of muscle fibre present. Chicken muscle can be classified into two types: slow oxidative muscle fibres and fast glycolytic muscle fibres. Slow oxidative muscle fibres, also known as Type I or slow-twitch fibres, are characterized by their relatively slow contraction speed and their use of aerobic respiration to produce ATP. These fibres are found predominantly in the legs and thighs of chickens, which require sustained activity and a constant supply of oxygen. They contain high levels of a protein called myoglobin that facilitates oxygen transport from the blood. Myoglobin, an iron-rich and red-pigmented protein, gives the dark meat its distinctive colour when cooked. It binds oxygen and stores it within the muscle fibres, helping them function for long periods without fatigue. Additionally, these fibres are extensively supplied with blood capillaries, further enhancing their oxygen supply.
In contrast, fast glycolytic muscle fibres, also known as Type II or fast-twitch fibres, exhibit rapid contractions and rely on anaerobic glycolysis as their primary energy source. These fibres are commonly found in chicken breasts and other muscle regions that are less active. They lack myoglobin but are capable of generating substantial force over short periods. Due to their lower oxygen requirements, they have a less substantial blood supply compared to slow oxidative fibres.
The difference in colour between dark and light meat in chickens can be attributed to the presence of myoglobin in slow oxidative muscle fibres. Myoglobin is an oxygen-binding molecule similar to haemoglobin in red blood cells. It plays a crucial role in oxygen transport and storage within muscle fibres. When chicken meat containing high levels of myoglobin is cooked, the oxygen-rich, red-pigmented myoglobin converts into metmyoglobin, resulting in the characteristic dark colour of the meat. This conversion occurs during cooking due to the heat-induced oxidation process.
The presence of slow oxidative muscle fibres and their associated myoglobin content is not limited to chickens but is also observed in other animals, including cattle. Research has shown that cattle exhibiting dark-cutting meat possess a higher proportion of oxidative muscle fibres. Specifically, dark-cutting bulls were found to have a greater number of slow oxidative fibres compared to normal bulls, contributing to the darker colour of their meat.
The colour of chicken muscle is, therefore, influenced by the type of muscle fibre present, with dark meat arising from the presence of slow oxidative muscle fibres and their associated myoglobin content. These fibres, designed for sustained activity and oxygen supply, contribute to the distinctive colour and functional characteristics of dark meat in chickens.
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Myoglobin in dark meat turns into metmyoglobin when cooked
The colour of meat depends on the presence of a protein called myoglobin. Myoglobin is a protein that facilitates oxygen transport from the blood. It is found in the muscle tissue of most mammals, including chicken. Myoglobin has three natural colours depending on its exposure to oxygen and the chemical state of the iron it contains. When meat is exposed to air, it turns bright red, indicating the presence of oxymyoglobin. When meat is vacuum-sealed, it appears purple-red, which is the deoxymyoglobin state. Meat appears tan or brown when there is very little oxygen present. This is because the iron in the pigment becomes oxidized. This oxidized state is called metmyoglobin, and it is the reason cooked chicken appears brown.
Chicken meat can be categorized into white and dark meat. Dark meat, found in the legs and thighs, has a higher presence of slow oxidative muscle fibres. These fibres have a rich supply of oxygen and generate low levels of force over long periods. They contain high levels of myoglobin, which is why they are called dark meat. When cooked, the myoglobin in dark meat turns into metmyoglobin, giving it a brown colour.
White meat, on the other hand, comes from animals with low levels of myoglobin or no myoglobin at all. Chicken breast, for example, is considered white meat because it lacks myoglobin. Fast glycolytic muscle fibres are found in chicken breast and other muscle regions that are not used actively. These fibres can generate a large force over a short time span.
The colour of meat can also change due to chemical changes over time. Meat that has been sitting at the supermarket or in a refrigerator for a few days will start to turn brown due to the myoglobin losing its red colour. However, this does not necessarily indicate spoilage, and the "sniff test" is recommended to determine if the meat is still safe to consume.
Additionally, the cooking process affects the colour of meat. When meat is cooked, the myoglobin darkens as it is exposed to heat and loses moisture. This is why a rare steak appears redder than a well-done steak, which takes on a grey colour.
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Indigenous chicken muscles have higher protein content
The colour of chicken muscle depends on the type of muscle fibre and its oxygen supply. Dark meat results from slow oxidative muscle fibres, which are used for sustained activity by active muscles such as those in the legs and thighs. These fibres contain high levels of myoglobin, an iron-rich, red-pigmented protein that facilitates oxygen transport from the blood. When cooked, myoglobin turns into metmyoglobin, giving dark meat its colour. On the other hand, fast glycolytic muscle fibres, which lack myoglobin, are found in chicken breast and other muscle regions that are not used as actively.
Indigenous chicken muscles have been found to contain higher protein contents than broiler muscles. In particular, studies have shown that the pectoralis and biceps femoris muscles of Thai indigenous chickens (Gallus domesticus) have higher protein contents than those of commercial breed (CP707) broiler chickens. Additionally, indigenous chicken muscles had lower fat and ash contents, with slightly higher levels of glutamic acid. They also contained more saturated and less polyunsaturated fatty acids than broiler muscles.
The housing system of chickens may also influence muscle fibre accretion. For instance, chickens raised in free-range conditions exhibited higher quantities of PAX3 and PAX7 mRNA and protein in their pectoralis major and thigh muscles compared to penned or caged chickens. This suggests that the expression of Pax3 and Pax7 genes may be coordinated by the housing system, impacting muscle development in adult chickens.
Furthermore, meat from indigenous chickens has been found to possess unique features that may increase their demand among consumers. For instance, indigenous chicken meat tends to be darker and redder, with lower fat content and a firmer texture compared to broiler meat. These characteristics can enhance the sensory experience and appeal to those who prefer chewy, low-fat chicken meat.
Overall, the higher protein content and favourable attributes of indigenous chicken muscles can contribute to their nutritional value and market desirability.
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Broiler chicken muscles have higher fat and ash content
The colour of chicken muscle depends on the type of muscle fibre present. Dark meat results from the predominant presence of slow oxidative muscle fibres, which are used for sustained activity by active muscles such as those in the legs and thighs. These muscle fibres contain high levels of myoglobin, an iron-rich, red-pigmented protein that facilitates oxygen transport from the blood. When cooked, myoglobin turns into metmyoglobin, which gives dark meat its colour. On the other hand, fast glycolytic muscle fibres are mainly found in chicken breast and other muscle regions that are not used actively. These muscle fibres lack myoglobin and are typically lighter in colour.
Broiler chickens, which are bred for rapid growth and heavy muscle development, have higher fat and ash content in their muscles compared to indigenous chickens. Specifically, the biceps femoris and pectoralis muscles of broiler chickens have been found to have higher fat and ash content than their indigenous counterparts. This difference in composition may be due to the selective breeding practices used in the broiler chicken industry, which prioritize rapid growth and muscle development.
The higher fat and ash content in broiler chicken muscles can have implications for both the birds' health and the quality of the meat they produce. For the birds themselves, the focus on rapid muscle growth can lead to bone deformities and injuries, as their bones may struggle to support the increased muscle mass. This has raised welfare concerns in the industry.
From a meat quality perspective, the higher fat content in broiler chicken muscles may impact the taste, texture, and nutritional profile of the meat. Higher fat content can affect the mouthfeel and flavour of the meat, potentially making it juicier and more flavourful. Additionally, the increased ash content, which is a measure of the mineral content in the muscles, can influence the overall nutritional value of the meat.
While the higher fat and ash content in broiler chicken muscles may have some implications, it is important to consider the context of the specific chicken breed, rearing practices, and consumer preferences. The fat and ash content can vary between different breeds of broiler chickens, and selective breeding practices can further modify these characteristics. Ultimately, the desired fat and ash levels in chicken meat depend on the intended use and the preferences of consumers, with some favouring the juiciness and flavour associated with higher fat content, while others may seek leaner options.
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Frequently asked questions
Chicken muscle can be either white or a darker colour, depending on the part of the chicken and how active those muscles are.
The colour of chicken muscle depends on the type of muscle fibre present. Dark meat is the result of slow oxidative muscle fibres, which are used for sustained activity by active muscles in the legs and thighs. These fibres contain high levels of the protein myoglobin, which is rich in iron and gives the meat its colour. White meat comes from fast glycolytic muscle fibres, which are found in chicken breasts and wings and are capable of generating large force over a short time span.
No, the colour of chicken muscle is determined by the type of activity, not the amount. For example, a chicken that flies for a long time will not develop red breast meat like a duck.
Yes, the breed of chicken can also affect the colour of the muscle. For example, the meat of Thai indigenous chickens tends to be lighter in colour than that of commercial broiler breeds.
Dark meat contains more heme iron than white meat due to the higher levels of myoglobin and hemoglobin. Heme iron is easily absorbed by the body and is an important nutrient. However, white meat may be lower in fat and calories, so it is considered a leaner option.
