Meat: Postmortem Muscular Manifestation

Meat constitutes the edible portion derived from the remains of living animals, encompassing both domesticated species like cattle, hogs, sheep, goats, and poultry, and wild animals such as deer, rabbit, and fish.

Considering that the primary constituent of edible animal tissue is muscular, it can be conveniently recognized as the postmortem expression of muscles.

Striated muscles are categorized as either cardiac or skeletal. Cardiac muscles are confined to the heart and are consistently engaged in pumping and circulating blood throughout the body.

Skeletal muscles, identifiable by their striated appearance, are attached to the backbone and participate in voluntary movements, contributing to both locomotion and posture. These muscles exhibit a diverse range of shapes, sizes, anatomical locations, and physiological functions.

The structure of skeletal muscles is intricate, encompassing not only muscle fibers but also connective, adipose, vascular, and nervous tissues. The essential qualities that consumers value in meat, such as color, texture (including tenderness and juiciness), and flavor, hinge on the structural and chemical makeup of the muscle.

Roughly 90% of a skeletal muscle is composed of muscle fibers, while the remaining 10% comprises connective and fat tissues. A muscle is typically enveloped by a dense layer of connective tissue called the epimysium and further divided into bundles of fibers by the perimysium. The individual muscle fibers are encased by a plasma membrane, surrounded by a thin layer of connective tissue known as the endomysium.

Skeletal muscles play a pivotal role in regulating locomotion, maintaining posture, and protecting vital organs. On average, a meat animal carcass contains approximately 100 bilaterally symmetrical pairs of individually distinctive muscles, varying in size, shape, color, and tendon concentration based on their respective functions and locations.
Meat: Postmortem Muscular Manifestation

Actin in muscle tissue

Muscle tissue is primarily composed of only a few types of proteins, with myosin and action being the two most important types in cooking.

About two-thirds of the proteins in mammals are myofibrillar proteins. The amount of actin and myosin differs by animal types and region.

Actin is the second most abundant myofibrillar protein in the myofibrils of cardiac and skeletal muscles, composing approximately 20% of the total.

A monomeric actin molecule is a globular protein and is often referred to as G-actin. These globular monomer are then assembled into an actin filament, called F-actin.

The molecular weight of G-actin is approximately 42,000, the diameter of each G-actin misnomer is approximately 5.0 nm, and each thin filament in skeletal muscle contains approximately 400 molecules of actin.
Actin in muscle tissue

Epimysium of muscle

The individual muscle cells are encased in collagenous tissue that can be subdivided into the portion that is intimate contact with the cell called the basement membrane and a more distal portion called endomysium.

A group of fascicle of muscle cells is surrounded by a more robust collagenous connective tissue network called the perimysium.

An anatomical muscle consists of group of fascicles and is surrounded by the epimysium. It is a thick layer of connective tissue around the entire muscle. It is through the epimysium that the main product of muscle (shortening) is coupled to bone via the myotendinous junction.

The epimysium is generally easily separated from the body of the muscle, whereas perimysium and endomysium are not practically separated from meat.

The epimysium is generally continuous with the tendons. In some cases, the epimysium may appear to extend into the body of the muscle.
Epimysium of muscle

Components of myofibrils

The most obvious structures within the muscle fiber are the myofibrils which are the units responsible for contraction and relaxation of the fiber.

Each myofibril consists of two sets of filaments: a thick set of filaments containing the protein myosin and thin set of filaments containing the protein actin. These two sets are arranged within the myofibril.

It is the light and dark bands of the myofibrils that give the muscle fiber its striated appearance. The dark, anisotropic, A-Bands correspond to the presence of myosin (thick) filaments, while the light, isotropic, I-bands contain the actin (thin) filaments.

In the center of the light I-band the line is called Z-line. Actin filaments are attached to these Z lines (or Z disc) and extend in both directions.

The thin filament (I bands) extend longitudinally from Z lines, which the thick filament (A band) span the gaps between the tips of the opposing actin units.

Components of myofibrils

Myofibrils of muscle fiber

Skeletal muscles vary in shape and size. The central portion of a whole muscle is called the belly. The belly comprises smaller compartments called fascicule.

Each fasciculus consists in turn of approximately 100 to 150 individual muscle fibers that range from 1 to 40 micrometers in length and 10 micrometers in dimeter.

A muscle fiber comprises a number of long, thin, cylindrical rods known as myofibrils, the essential contractile units of muscle, which are separated from one another by a highlight specialized network of tubules the sarcoplasmic reticulum.

The sarcoplasmic reticulum, a specialized organelle that’s stores and releases calcium, is an interconnecting network of tubules running parallel with and wrapped around the myofibrils.

The major significant of the sarcoplasmic reticulum is its ability to store, release and take up calcium and thereby control muscle contraction.

Myofibrils are bathed in an aqueous fluid (sarcoplasm), which is about 75-80% water and contains mitochondria, enzymes, glycogen, adenosine triphosphate, creatine, phosphate and myoglobin.

Myofibrils range in diameter from 1 to 2 micrometers. They are grouped in clusters and run the length of the muscle fiber. In turn each myofibril comprises long, thin strands of serially linked sarcomeres. Sarcomeres are the functional unit of a muscle.
Myofibrils of muscle fiber

What is meat?

Meats consumption by the hunter-gatherers predated the agricultural revolution, of which it then became an integral part.

Meat is defined as the flesh of cattle, swine, sheep or goats that is consumed for food. Beef meat is from cattle, including bulls, claves, cows, steers and oxen.

Cattle, sheep and pigs are often referred to as ‘red meat’ species and poultry as ‘white meat’. Meat consists of muscle fibers held together by connective tissue and interspersed with nerve and blood vessels, which normally accompany tissue.

Connective tissue is a fibrous structure composed primarily of collagen fibrils. A single muscle contains a number of fiber bundles, held together by sheath of connective tissue, epimysium.

Group fiber is associated into fiber bundles which in turn, are surrounded by a sheath of connective tissue, by perimysium. The basic unit of muscle is the fiber, and it is bounded by the endomysium and sarcolemma.

Muscles in mature animals have higher contents of collagen cross-links than the same muscles from young animals. The type of collagen cross-link is also different; as the animal age increases many of the collagen cross-links are transformed from a soluble type to an insoluble type, resulting in increased toughness of meat.

All meat sold in United States must be inspected for wholesomeness by the government, usually by the USDA nationwide. USDA also grades meat.  Beef cuts are judged by the palatability characteristics of the meats.
What is meat?