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University of Baghdad College of Veterinary Medicine Dept. of Vet. Public Health/ Meat Hygiene Division Meat Hygiene Course/ 5th. Year 2015-2016
Theory Lecture #: 3 2nd.Semester
Conversion of Muscle to Meat (Rigor mortis)
Muscle There are three types of muscle found in an animal carcass:
1) Skeletal muscle.
2) Smooth muscle.
3) Cardiac muscle.
Skeletal muscle (also known as voluntary muscle) makes up 35 to 65 percent of the carcass weight of a typical animal.
These are the muscles which allow an animal to move its body at will. They can be attached to bones, ligaments, fascia, cartilage, or skin.
There are two types of muscle fibers : red and white .
▶ While most muscles are composed of both red and white fibers, the intensity of the muscle color is due to the proportion of red fibers to white fibers.
▶ Muscles which appear red (such as the leg muscles of chicken and turkeys) have a higher proportion of red fibers than muscles which appear white (such as the breast muscles of chicken and turkey).
▶ Red muscle fibers have a higher myoglobin content which gives them their red color.
▶ Smooth muscle is much less abundant. It is primarily found in the walls of arteries, lymph vessels, and in the gastrointestinal and reproductive tracts.
▶ Cardiac muscle is found in the heart of the animal. It has the unique ability to contract rhythmically from early embryonic life until death. Like the skeletal muscle, it has microscopic banding (striations).
Adipose Tissue
▶ Adipose tissue is fat.
▶ The bodies of many animals species have two types of fat:
1) White fat
2) Brown fat. Page 3 of 8
▶ Most adipose tissue is white fat, but brown fat is present at birth, especially around the kidneys.
▶ Most brown fat is converted to white fat a few weeks after birth, but in some animals persists into adulthood.
Blood and Lymph
▶ Blood normally constitutes about 7 percent of the body weight of mammals.
▶ Blood consists primarily of three types of blood cells and the plasma in which they are suspended.
▶ The three types of blood cells are:
1) Platelets which stop bleeding by causing clot formation,
2) Red blood cells which carry oxygen and nutrients throughout the body,
3) White blood cells which fight infection.
4) Lymph is a fluid which circulates continually and passes through all tissues, organs, and lymph nodes of the body.
5) Lymph helps to carry dissolved nutrients to the body's tissues as it diffuses through very thin capillary walls.
6) It also plays a part in the body's immune defense as it flows through lymph nodes which filter out harmful foreign particles such as bacteria and cancerous cells.
composition of meat
▶ In general, meat is composed of: 1) water,
2) fat,
3) protein,
4) minerals
5) a small proportion of carbohydrate.
▶ The most valuable component from the nutritional and processing point of view is protein.
▶ Protein contents and values define the quality of the raw meat material and its suitability for further processing.
▶ Protein content is also the criterion for the quality and value of the finished processed meat products.
▶ The value of animal foods is essentially associated with their content of proteins.
▶ Protein is made up of about 20 amino acids.
. Approximately 65% of the proteins in the animal body are skeleton muscle protein,
. 30% connective tissue proteins (collagen, elastin)
. the remaining 5% blood proteins and keratin (hairs, nails).
Histological structure of muscle tissue Page 5 of 8
▶ The muscles are surrounded by a connective tissue membrane, whose ends meet and merge into a tendon attached to the skeleton (Fig. 1(b)).
▶ The structure of muscle resembles wires in a cable.
▶ Strands of fibers are grouped together in systems with connective tissue holding the system together.
▶ The connective tissue network is designed to combine and transmit the force of contraction to accomplish movement.
▶ As a result, there is a complex network in muscle beginning with an exterior muscle cover termed the epimysium.
▶ A subdivision of the epimysium divides the muscle into several muscle bundles which are visible to the naked eye and the connective tissue around each bundle is referred to as the perimysium.
▶ Between the muscle bundles are blood vessels as well as connective tissue and fat deposits.
▶ Finally, within each bundle are several muscle fibers or muscle cells each surrounded by connective tissue called endomysium.
The size and diameter of muscle fibers depends on 1. age, 2. type 3. Breed of animals.
Each muscle fiber (muscle cell) is surrounded by a cell membrane (sarcolemma). Inside the cell are sarcoplasma and a large number of filaments, also called myofibrils.
o The sarcoplasm is a soft protein structure and contains amongst others the red muscle pigment myoglobin.
• Myoglobin absorbs oxygen carried by the small blood vessels and serves as an oxygen reserve for contraction of the living muscle. • In meat the myoglobin provides the red meat color and plays a decisive role in the curing reaction.
▶ The sarcomere is the unit of muscle structure between the two Z lines (Fig. 1).
Other bands that can be observed with the light microscope include the A band, H band.
Areas that appear darkest are the Z line and the regions of the A band where thick (Myosin) and thin (Actin) filaments overlap.
The sarcomere length changes depending on the contractile state of the muscle.
The thick and thin filaments do not change length, but the degree of overlap between thick and thin filaments changes. Page 7 of 8 Dr. Zuhair Ahmed
MSc & PhD Meat Science & Hygiene