Logan Steele
Fish fillets are a popular food product, with fish providing almost 16% of the animal protein consumed globally. The fillet consists of two bundles of large lateral muscles that run on either side of the backbone. The term muscle and fillet are often used interchangeably, but there are some differences in common usage. The muscle structure of fish is complex, consisting of myosepta, myomeres, myotomes, myofibrils, and sarcomeres. The unique sensory characteristics of fish, such as flavor, color, odor, and texture, are determined by their chemical composition. Heating fish fillets changes their color and texture, and can also prolong their shelf life.
Characteristics and Values of Fish Fillet Muscle
| Characteristics | Values |
|---|---|
| Definition | The flesh of a fish which has been cut or sliced away from the bone by cutting lengthwise along one side of the fish parallel to the backbone. |
| Composition | The fillet consists of two bundles of large lateral muscles that run on both sides of the backbone. |
| Connective Tissue | Myocommata, a thin connective tissue membrane, divides fish muscle into muscle blocks known as myotomes. |
| Muscle Fibers | Each myotome is composed of muscle fibers generally less than 20 mm long and 0.02–1 mm in diameter. |
| Myofibrils | Each muscle fiber contains 1000–2000 myofibrils, with diameters ranging between 1–2 µm. |
| Sarcomeres | The myofibril consists of small subunits named sarcomeres, composed of the main contractile proteins, actin (thin filament) and myosin (thick filament). |
| Collagen Content | The intramuscular connective tissues mostly consist of sheets of collagen, which affects the textural properties of the fish muscle, such as firmness. |
| Color | The superficial lateral red muscle, which is rich in myoglobin, exhibits a generally brown color, while the white muscle is translucent. |
| Taste and Flavor | Heating methods such as boiling, baking, roasting, frying, and grilling enhance the taste and flavor of fish fillets. |
| Texture | Upon heating, the muscle becomes opaque and firm, and the collagen network gelatinizes, resulting in a flake-like texture. |
| Protein Denaturation | Thermal denaturation of muscle involves the unfolding of protein molecules due to the breakage of intermolecular hydrogen bonds, reducing water binding capacity and shrinkage of the muscle. |
| Waste | In the preparation of fish, up to 50% of the whole fish is commonly discarded as waste, including skeletal structure, intestinal organs, and edible fish muscle that cannot be easily removed from the bone structure. |
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What You'll Learn
Fish fillets are made up of two bundles of lateral muscles
Fish fillets are a popular food product, providing almost 16% of the animal protein consumed by humans globally. They are prepared by cutting the flesh of a fish lengthwise along one side of the fish, parallel to the backbone. This process is repeated on the other side to produce a double fillet.
The fish fillet consists of two bundles of large lateral muscles that run on both sides of the backbone. These muscles are separated by a thin connective tissue membrane called "myocommata", which divides the muscle into muscle blocks known as "myotomes". Each myotome is made up of muscle fibres generally less than 20 mm long and 0.02-1 mm in diameter. Each muscle fibre contains 1000-2000 "myofibrils", which consist of small subunits called "sarcomeres" composed of the main contractile proteins, actin and myosin. The intramuscular connective tissues are composed of sheets of collagen, which directly affect the textural properties of the fish muscle, such as firmness.
The muscle structure of fish is more complex than that of terrestrial animals, with three main types of muscle: a major white muscle, a superficial red muscle (along the skin), and an intermediate pink muscle. These muscles are present in each myomere, with intramuscular adipose tissue located within the myomere and between the muscle fibres. The red muscle, which is rich in myoglobin, exhibits an intense brown colour, while the white muscle is translucent. In salmonids, the presence of carotenoid pigments in the muscle fibres gives the flesh its orange-red colour.
The chemical composition of these muscle types can vary within the same species, as seen in pink salmon and albacore tuna. These muscles also play different physiological roles in fish. The unique structure and composition of fish muscle influence the quality of meat and flesh, including its colour, flavour, and texture. For example, heating the muscle causes protein denaturation, leading to changes in colour and texture.
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The colour of fish fillets is influenced by the presence of myoglobin
Fish is a primary source of protein and other nutrients, and its unique sensory characteristics, such as flavour, colour, odour, and texture, make it popular among consumers. The colour of meat is one of the vital criteria indicating its freshness, quality, and acceptability. The colour of fish fillets, or fish muscle, is influenced by the presence of myoglobin, an oxygen-carrying protein in muscle.
Myoglobin is an iron-rich protein that gives meat its colour. It stores oxygen in muscle cells, similar to how haemoglobin stores oxygen in blood cells. The more myoglobin content meat contains, the darker red it will appear in colour. Myoglobin content is higher in beef and lower in poultry, with lamb and pork having intermediate amounts. The age of the animal will also impact the myoglobin content of the muscles, with older animals having more myoglobin and darker meat.
In fish, the fillet consists of two bundles of large lateral muscles that run on either side of the backbone. The red muscle cells primarily rely on aerobic metabolism (using oxygen) to provide energy for consistent muscle work and are richer in lipids, nucleic acids, myoglobin, and vitamin B compared to white muscle cells. The red muscle usually lies directly under the skin along the side of the body and, in certain active species, also in a band near the spine. The red muscle is similar to the heart muscle in that it is rich in mitochondria, is well supplied with capillaries, and has a higher content of myoglobin, resulting in greater oxygen availability.
The difference in colour between white and red fish fillets depends on the amount of myoglobin and the type of food the fish consumes. The red muscle, with its higher myoglobin content, exhibits an intense (generally brown) colour, while the white muscle is rather translucent. The pink colour found in salmon and sea trout, on the other hand, does not stem from myoglobin content but from the consumption of crustaceans, which contain the red carotenoid astaxanthin.
The colour of fish fillets can also be influenced by other factors, such as chemical composition, post-harvest handling, storage, processing, and cooking methods. Heating, for example, can cause denaturation of muscle proteins and pigments, leading to oxidation and colour changes.
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Fish fillets are commonly regarded as boneless
The term "fillet" refers to the flesh of a fish that has been cut or sliced away from the bone by cutting lengthwise along one side of the fish, parallel to the backbone. This is in contrast to fish steaks, which are cut perpendicular to the spine and include the larger bones. The remaining bones with attached flesh after filleting are called the "frame" and are often used for making fish stock.
The fish fillet consists of two bundles of large lateral muscles that run on both sides of the backbone. These muscles are known as "myocommata" and are separated by a thin connective tissue membrane. Each muscle is composed of smaller muscle fibers, which contain contractile proteins such as actin and myosin. The muscle fibers themselves are surrounded by intramuscular connective tissues, primarily made up of collagen, which influences the textural properties of the fish muscle, such as firmness.
The color of the fish fillet is also influenced by the type of muscle it contains. The superficial lateral red muscle, rich in myoglobin, exhibits a brown color, while the white muscle appears translucent. In salmonids, the presence of carotenoid pigments, such as astaxanthin, contributes to the orange-red color of the flesh. Heating the fish fillet can further alter its color due to the denaturation of muscle proteins and pigments.
In summary, while fish fillets are generally considered boneless due to the absence of larger bones, they may contain smaller pin bones. The fillet consists of lateral muscles, muscle fibers, and connective tissues, contributing to its texture and color. Heating the fillet can affect its sensory characteristics, including flavor, color, odor, and texture.
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Fish is a primary source of protein
Fish is a rich source of high-quality protein and vital nutrients, making it an invaluable food. It contains healthy protein and many nutrients that are not found in comparable quantities and varieties in cereals, crops, or meat. These include certain fatty acids, vitamins, and minerals. Lean fish, such as pollock, cod, and haddock, are a source of low-fat muscle meat, containing 15 to 20% protein. Fatty fish, like salmon and mackerel, are a good source of omega-3 fatty acids and vitamin D, which is found in very few foods.
The unique combination of nutrients in fish provides multiple health benefits. For example, proteins containing selenium may help prevent cancer, while taurine is important for brain development and retinal tissue growth. Vitamin D is essential for human health and is mostly found in fatty fish. Fish also contain all the important amino acids for human nutrition, including essential amino acids, which the human body cannot produce on its own.
The muscle structure of fish consists of two bundles of large lateral muscles that run along both sides of the backbone. These muscles are divided into muscle blocks called "myotomes" by a thin connective tissue membrane called "myocommata." Each myotome is made up of muscle fibers, which contain contractile proteins like actin and myosin. The intramuscular connective tissues are primarily composed of collagen, which affects the textural properties of the fish muscle, such as firmness.
In summary, fish is a primary source of protein for a significant portion of the world's population, providing essential nutrients and contributing to food security, improved nutrition, and poverty alleviation. The muscle structure of fish is composed of various types of muscle fibers, connective tissues, and contractile proteins, which give it unique sensory characteristics and nutritional benefits.
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Fish fillets are a product of the fish processing method, filleting
The filleting method is a classic example of a processing approach that produces practically no waste material. Apart from the fillets, minced meat can be produced from the waste material, and the remainder sold as animal feed. The process is also profitable for small fish processing plants as it allows for the production of value-added products.
The filleting process varies slightly depending on the type of fish. For example, the process involved in filleting whitefish is moderately different compared to the filleting of oily fish. Oily fish, such as salmon, tuna, mackerel, herring, and anchovy, have oils throughout their tissues and in the stomach cavity around the gut. Up to 30% of oil is found in the fillet, varying across species. Due to the oil content, gutting and heading are avoided to reduce the risk associated with oily surfaces. The oily skin is kept as it retains the quality of the flesh.
The filleting process can be done manually or with the use of filleting machines. Hand filleting is hard work and requires skill and experience. Filleting machines work as long as different species are of the same size and have a similar body shape. They have two disk knives set at a distance equal to the thickness of the fish's backbone.
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Frequently asked questions
A fish fillet is the flesh of a fish that has been cut or sliced away from the bone by cutting lengthwise along one side of the fish parallel to the backbone. The term "fillet" is used interchangeably with "muscle" in this context, although there are some differences in common usage.
Fish fillets contain three main types of muscle: a major white muscle, a superficial red muscle (along the skin), and an intermediate pink muscle. These muscles are present in each myomere, which are bundles of large lateral muscles that run on both sides of the backbone.
Cooking fish fillets causes conformational changes in the muscle proteins, particularly contractile proteins, leading to protein denaturation. This results in the muscle becoming opaque and firm, with the collagen network gelatinizing and the muscle tissue disintegrating into a flake-like texture.
