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Meat is largely made up of muscle fibres, which are long protein strands. The muscle mass of livestock and fish species used for human food accounts for 35 to 60% of their body weight. The type of muscle fibres present in the meat influences its quality, including colour, tenderness, and pH. For example, meat with higher levels of Type I and Type IIa muscle fibres will be brighter red, while Type IIb muscle fibres result in paler meat. The direction of the formation of the muscle fibres is known as the grain of the meat.
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What You'll Learn
Meat quality is influenced by muscle fibre composition
Meat is primarily composed of skeletal muscle, which makes up 35 to 60% of the body weight of livestock and fish species used for human food. Skeletal muscle is made up of muscle fibres and connective and adipose tissues. The muscle fibres are surrounded by loose connective tissue, which consists of cells and an extracellular matrix (ECM) that primarily consists of a composite network of collagen fibres.
Skeletal muscle consists of two types of muscle fibres: red (slow-twitch) fibres and white (fast-twitch) fibres. The composition of these fibre types directly influences meat quality attributes such as colour, tenderness, post-slaughter pH, and water-holding capacity. The colour of meat is primarily determined by the concentrations of myoglobin and haemoglobin present within muscle fibres. Type I and Type IIa muscle fibres have higher myoglobin levels, resulting in a bright red appearance, while Type IIb muscle fibres exhibit lower myoglobin levels, leading to a paler meat colour. The presence of Type IIb muscle fibres in skeletal muscle tissue is inversely related to meat quality.
The water-holding capacity of meat is influenced by the rate and extent of decrease in post-mortem pH. A high rate combined with a high muscle temperature can cause denaturation of muscle proteins, reducing the water-holding capacity and increasing cooking loss. The pH value of muscle tissue is influenced by the glycogen content and the rate of adenosine triphosphate (ATP) degradation within the animal's muscles at the time of slaughter. Type IIb muscle fibres, known for their glycolytic properties, contain high levels of glycogen and display significant ATP enzyme activity, resulting in a rapid decrease in pH value.
The texture of meat is also influenced by muscle fibre composition. The finer the texture, the more precision of movement from the muscle, such as the tenderloin. Coarse-textured muscles, such as shanks and shoulders, are the heavy working muscles that support the full weight of the animal and require less precision of movement.
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Meat colour is determined by muscle fibre type
Meat colour is indeed determined by muscle fibre type, but it is also influenced by a host of other factors. Meat colour is one of the key indicators of meat quality, along with pH, water-holding capacity, tenderness, and flavour. The quality of meat is largely dependent on muscle fibre characteristics, and the colour of meat is primarily determined by the concentrations of myoglobin and haemoglobin present within the muscle fibres.
There are three types of skeletal muscle, known as twitch fibres, with differing speeds of movement and colours. Fast glycolytic (white) fibres are found in skeletal muscles such as shanks, shoulders, and hips, and are known as voluntary muscles. They require no oxygen and move faster. The other two types are red (slow-twitch) fibres and white (fast-twitch) fibres. The red fibres have higher myoglobin content, resulting in a bright red appearance, while the white fibres have lower myoglobin content and lead to a paler meat colour.
Research has shown a positive correlation between the intensity of redness in meat and the proportion of Type I and Type IIa muscle fibres within the muscle structure. Type IIb muscle fibres exhibit lower myoglobin levels, which results in paler meat. Type IIb fibres are also known for their glycolytic properties, which can lead to a swift decrease in pH value, causing the meat to become pale, soft, and exudative.
The colour of meat is also influenced by various intrinsic and extrinsic factors, including breed, genotype, sex, hormones, growth performance, diet, muscle location, exercise, and ambient temperature. The histochemical characteristics of skeletal muscle are primarily the result of genetic and environmental factors.
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Tenderness of meat is influenced by muscle fibre type
Meat is predominantly made up of muscle fibres. Skeletal muscle, the most common muscle type in animals, is composed of two types of muscle fibres: red (slow-twitch) and white (fast-twitch). The tenderness of meat is influenced by the type of muscle fibre, as well as other factors such as the diameter, type, and quantity of muscle fibres, and the amount of connective and fat tissues.
Slow-twitch (Type I) and fast-twitch (Type II) muscle fibres are further divided into subtypes. Type II fibres, for instance, are divided into Type IIa, Type IIx, and Type IIb. The presence of Type I and Type IIa muscle fibres is positively associated with meat quality, whereas the presence of Type IIb muscle fibres is negatively associated with meat quality.
The colour of meat is primarily determined by the concentrations of myoglobin and hemoglobin present within muscle fibres. Type I and Type IIa muscle fibres have higher myoglobin levels, resulting in a bright red appearance, while Type IIb muscle fibres have lower myoglobin levels, resulting in a paler meat colour. Research has shown a positive correlation between the intensity of redness in meat and the proportion of Type I and Type IIa muscle fibres.
The texture of the muscles is determined by the bundle size and thickness of the connective tissue septa. Muscles with small bundles and thin septa have a fine texture, while those with larger bundles and thicker septa have a coarser texture. The finer the texture, the more precise the movement of the muscle. For example, the tenderloin has a fine texture and is a precision muscle, whereas the shoulder has a coarser texture and is a heavy working muscle that supports the full weight of the animal.
The pH value of muscle tissue is influenced by the glycogen content and the rate of adenosine triphosphate (ATP) degradation within the animal's muscles at the time of slaughter. Type IIb muscle fibres, known for their glycolytic properties, contain high levels of glycogen and exhibit significant ATP enzyme activity, resulting in rapid glycolysis and a swift decrease in pH value. Low pH values may cause the denaturation of muscle fibre proteins, leading to pale, soft, and exudative (PSE) meat.
In summary, the tenderness of meat is influenced by muscle fibre type, with Type I and Type IIa muscle fibres being associated with higher meat quality and tenderness, and Type IIb muscle fibres being associated with lower meat quality. Other factors such as muscle fibre composition, diameter, quantity, and connective and fat tissues also play a role in determining meat tenderness and quality.
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Moisture loss in meat is related to temperature
Meat is largely made up of muscle fibres, with skeletal muscle accounting for 35 to 60% of the body weight of livestock and fish species. The quality of meat is influenced by the structure and composition of these muscle fibres.
Moisture content is an important factor in the quality, taste, and safety of meat. Meat naturally has high moisture levels, with the U.S. Department of Agriculture reporting that muscle tissue is about 75% water, 20% protein, and 5% minerals, carbohydrates, and fats. Leaner meats tend to contain more water because water is essential for protein synthesis, which builds muscle.
Moisture loss in meat is influenced by temperature. During cooking, temperature-induced denaturation or structural changes in meat proteins can cause moisture loss. For example, myosin molecules start to denature at 40°C and completely denature when heated above 53°C. Similarly, severe shrinkage of collagen fibres starts at 57°C, and actin denaturation and shrinkage of myofibrils start at 66°C to 73°C. Cooking meat at higher temperatures leads to shrinkage first transverse to the fibre axes at about 40°C to 60°C and then parallel to the muscle fibres at about 60°C to 90°C.
Research has shown that moisture loss in meat increases at higher temperatures. In a study on the effect of meat temperature on moisture loss in broiler breast meat, samples were sorted into normal, woody breast (WB), and pale, soft, and exudative (PSE) groups. The samples were subjected to different temperatures ranging from 23°C to 90°C. The results indicated that moisture loss in the WB samples was greater than in the normal and PSE groups at temperatures of 68°C or 90°C, with the least moisture loss occurring at 53°C.
The relationship between temperature and moisture loss in meat is complex and influenced by various factors such as the type of meat, pH, and cooking method. Understanding this relationship is crucial for maintaining the quality, taste, and safety of meat products.
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Connective tissue and fat influence meat quality
Meat is composed of muscle fibres and connective and fat tissues. Skeletal muscle, the predominant muscle type in animals, is primarily composed of two types of muscle fibres: red (slow-twitch) fibres and white (fast-twitch) fibres. The content and composition of these different muscle fibre types directly influence meat quality indicators such as colour, tenderness, pH, and water-holding capacity.
The colour of meat is primarily determined by the concentrations of myoglobin and haemoglobin present within muscle fibres. Type I and Type IIa muscle fibres possess higher myoglobin levels, resulting in a bright red appearance, while Type IIb muscle fibres exhibit lower myoglobin levels, leading to a paler meat colour. The presence of Type IIb muscle fibres in skeletal muscle tissue is inversely related to meat quality, while the proportion of Type I and Type IIa muscle fibres is positively associated with meat quality.
The amount, distribution, and composition of connective tissue within muscle vary with muscle position in the carcass and animal age. Connective tissue plays a role in determining meat texture and toughness, with the perimysial component of intramuscular connective tissue (IMCT) being the most involved in defining the mechanical integrity of cooked meat. Meat tenderness generally decreases with animal age, and collagen-rich muscles show a more significant decrease than those with low IMCT content. The amount and thermal stability of IMCT collagen can be manipulated by factors such as growth rate, animal nutrition, and exercise.
Fat and long-chain fatty acids, whether in adipose tissue or muscle, contribute to important aspects of meat quality, including nutritional and sensory values. The lipid composition of intramuscular fat influences meat appearance, colour, tenderness, juiciness, flavour, and technological value. In fish, the edible part, or fillets, consists of several muscles separated by connective tissue sheaths, which contribute to the texture and quality of the flesh.
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Frequently asked questions
Meat fibres are the long protein fibre strands that make up the muscle meat of land animals. Each muscle fibre is a multinucleated cell made up of bundles of myofibrils.
There are two main types of muscle fibres: red (slow-twitch) fibres and white (fast-twitch) fibres. White fibres can be further divided into Fast Glycolytic (white) and three types of fast-twitch fibres: Type IIa, Type IIx, and Type IIb.
The content and composition of different muscle fibre types directly influence meat quality indicators such as colour, tenderness, pH, flavour, and water-holding capacity. For example, Type I and Type IIa muscle fibres have higher myoglobin levels, resulting in a bright red appearance, while Type IIb muscle fibres exhibit lower myoglobin levels, leading to a paler meat colour.
Heat causes changes in the texture and moisture-holding capacity of meat. Myosin and actin, the myofibrillar proteins within each sarcomere, are responsible for these changes. Myosin denatures around 104°F (40°C) and this change is what makes meat go from raw to being cooked and tender. Actin denatures at a higher temperature range, and this reaction is what makes meat tough and dry.
