A. MUSCLE STRUCTURE AND COMPOSITION
1. Meat as a Food
Meat is the edible portion of animal tissues, consisting primarily of skeletal muscle, together with variable amounts of connective tissue, adipose tissue, bone-associated tissues, blood vessels, and other components.
2. Major Meat-Producing Animals
Important meat-producing species worldwide include cattle, buffalo, sheep, goats, pigs, poultry, and various game animals. The relative importance of each species differs among countries, production systems, dietary practices, and cultural traditions.
3. Skeletal Muscle
Skeletal muscle is the principal tissue used for most fresh meat products. It is composed of muscle fibres, connective tissue, blood vessels, nerves, and associated structural components.
4. Types of Muscle
Muscle tissue is classified into skeletal, cardiac, and smooth muscle. Skeletal and cardiac muscles are striated, whereas smooth muscle lacks the characteristic striated appearance. Skeletal muscle is generally under voluntary control, while cardiac and smooth muscles are involuntary.
5. Connective Tissue in Meat
Important connective tissues associated with meat include collagenous and elastic tissues, adipose tissue, cartilage, and bone-associated tissues. Connective tissue has a major influence on meat texture and tenderness.
6. Epimysium
The epimysium is a connective-tissue sheath surrounding an entire skeletal muscle. Other connective-tissue layers include the perimysium around muscle fibre bundles and the endomysium surrounding individual muscle fibres.
7. Skeletal Muscle Fibres
Skeletal muscle fibres are long, cylindrical, multinucleated cells containing numerous myofibrils. Their diameter, metabolic characteristics, and contractile properties vary among muscles and species.
8. Muscle Fibre Types
Muscle fibres can be broadly characterized according to their metabolic properties as oxidative, glycolytic, and intermediate types. Oxidative fibres generally contain more mitochondria and myoglobin, whereas glycolytic fibres rely more heavily on anaerobic metabolism.
9. Sarcomere
The sarcomere is the fundamental contractile unit of the myofibril. It contains thick filaments composed mainly of myosin and thin filaments composed mainly of actin.
10. Myofibrillar Proteins
Myofibrillar proteins include myosin, actin, tropomyosin, troponin, and associated proteins. They are responsible for muscle contraction and contribute importantly to the functional properties and texture of meat.
11. Tendons and Ligaments
Tendons connect muscles to bones, whereas ligaments connect bones to one another and contribute to joint stability. Both contain substantial connective tissue.
12. Water in Muscle
Water is the major component of fresh muscle. Its proportion varies according to species, muscle, fat content, age, nutritional status, and processing conditions. Muscle water exists in different physical states and is associated with proteins and other cellular structures.
13. Protein in Muscle
Proteins are major structural and functional components of muscle. They are commonly divided into myofibrillar, sarcoplasmic, and connective-tissue proteins according to their location and solubility characteristics.
14. Myofibrillar Proteins and Water-Holding Capacity
Myofibrillar proteins, particularly myosin and actin, contribute strongly to the water-holding capacity, emulsification, gel formation, and texture of meat products. Their functionality is affected by pH, ionic strength, temperature, and postmortem changes.
15. Collagen
Collagen is the principal structural protein of connective tissue and is an important determinant of meat toughness. Its amount, distribution, thermal stability, and degree of cross-linking vary with species, muscle, age, and anatomical function.
B. CONNECTIVE TISSUE, FAT AND POSTMORTEM METABOLISM
16. Collagen and Gelatin
When collagen is heated in the presence of sufficient moisture, its ordered structure is disrupted and collagen can progressively convert into gelatin. The rate of conversion depends on temperature, time, moisture, collagen cross-linking, and tissue characteristics.
17. Tropocollagen
Tropocollagen is the basic molecular unit from which collagen fibrils are assembled. It consists of three polypeptide chains arranged in a characteristic triple-helical structure.
18. Meat Lipids
Lipids occur as subcutaneous, intermuscular, and intramuscular fat. They contribute to energy density, flavour, juiciness, appearance, and texture. Lipid composition varies among species, tissues, diets, and production systems.
19. Marbling
Marbling refers to visible deposits of intramuscular fat distributed within skeletal muscle. The amount and distribution of marbling can influence flavour, juiciness, tenderness perception, and cooking characteristics.
20. Muscle Glycogen
Glycogen is the principal carbohydrate reserve in skeletal muscle. The amount present at slaughter is influenced by nutrition, exercise, stress, fasting, and physiological condition.
21. Postmortem Glycolysis
After slaughter, oxygen delivery to muscle ceases and metabolism shifts toward predominantly anaerobic glycolysis. Stored glycogen is converted through glycolysis, producing lactate and contributing to a decline in muscle pH.
22. Importance of Postmortem Glycolysis
The rate and extent of postmortem glycolysis influence pH decline, colour, water-holding capacity, tenderness, microbial stability, and processing characteristics of meat.
23. Minerals in Meat
Meat contains minerals including phosphorus, potassium, sodium, magnesium, iron, and zinc. Mineral concentration varies among species, muscles, tissues, diets, and processing conditions.
24. Vitamins in Meat
Meat provides several vitamins, particularly B-group vitamins, although the concentration varies among species and tissues. Fat-soluble vitamins are more closely associated with adipose and organ tissues.
25. Effect of Stress Before Slaughter
Severe or prolonged pre-slaughter stress can alter muscle energy reserves and postmortem metabolism. Excessive stress may reduce muscle glycogen and adversely affect meat quality.
26. Dark, Firm and Dry Meat
When muscle glycogen reserves are substantially depleted before slaughter, postmortem acidification may be insufficient and the ultimate pH remains relatively high. In beef and some other red meats, this condition is associated with dark, firm, dry (DFD) meat, which generally has a dark appearance, firm texture, and reduced storage stability.
27. Pale, Soft and Exudative Pork
Very rapid postmortem glycolysis and pH decline while the carcass is still warm can contribute to pale, soft, exudative (PSE) pork. PSE meat commonly has pale colour, poor water-holding capacity, and increased drip and cooking losses.
C. POSTMORTEM CHANGES AND MEAT QUALITY
28. Stunning
Stunning is a procedure used in many slaughter systems to render an animal unconscious or insensible before slaughter. The method and legal requirements vary according to species, jurisdiction, equipment, and applicable animal-welfare regulations.
29. Carcass Cutting
Carcass cutting involves separating the carcass into primal, subprimal, and retail cuts according to anatomical structure, processing requirements, commercial practice, and consumer preferences.
30. Meat Inspection
Post-mortem meat inspection involves examination of the carcass and relevant organs and tissues to identify abnormalities, disease conditions, contamination, or other conditions affecting food safety and suitability for human consumption. Procedures vary according to species and national regulations.
31. pH Decline After Slaughter
The pH of living muscle is near physiological neutrality. After slaughter, anaerobic glycolysis produces lactate and causes muscle pH to decline. The rate and final extent of this decline vary among species, muscles, animals, and processing conditions.
32. Rigor Mortis
Rigor mortis is the postmortem stiffening of muscle associated mainly with depletion of ATP and the formation of stable actomyosin cross-bridges. Its development is influenced by temperature, muscle type, glycogen availability, and postmortem metabolism.
33. Water-Holding Capacity
Water-holding capacity (WHC) is the ability of meat to retain its water during storage and when subjected to external forces such as cutting, pressing, freezing, thawing, and cooking. WHC strongly affects product yield and quality.
34. Factors Affecting Water-Holding Capacity
Meat WHC is influenced by pH, protein structure, rigor development, temperature, ionic strength, freezing and thawing, mechanical treatment, and storage conditions. Changes in myofibrillar protein structure can substantially alter water retention.
35. Meat Tenderness
Tenderness is influenced by connective-tissue content, collagen cross-linking, sarcomere length, postmortem proteolysis, muscle fibre characteristics, animal age, processing, and cooking conditions.
36. Meat Colour
Meat colour is influenced principally by myoglobin, together with oxygen availability, pH, temperature, packaging atmosphere, light exposure, and oxidation state of the pigment.
37. Myoglobin
Myoglobin is the principal pigment responsible for the characteristic colour of muscle. It contains a heme group with iron and exists in different chemical states that produce different meat colours.
38. Deoxymyoglobin
In oxygen-depleted meat, myoglobin is predominantly present as deoxymyoglobin, which contributes to a dark purplish-red appearance.
39. Oxymyoglobin
When freshly cut meat is exposed to oxygen, myoglobin binds oxygen and forms oxymyoglobin, producing the bright red colour commonly associated with oxygenated fresh meat.
40. Metmyoglobin
Oxidation of the iron in myoglobin produces metmyoglobin, which is associated with brown discoloration. The formation of metmyoglobin is influenced by oxygen availability, pH, temperature, storage time, lipid oxidation, and packaging conditions.
D. CHILLING, FREEZING AND MEAT PROCESSING
41. Chilling of Meat
Chilling reduces meat temperature after slaughter and slows microbial growth and biochemical reactions. Chilling rate must be controlled because excessively rapid chilling of susceptible pre-rigor muscles can contribute to cold shortening.
42. Cold Shortening
Cold shortening occurs when certain pre-rigor muscles are chilled too rapidly. Excessive calcium release and muscle contraction can cause sarcomere shortening and increased toughness. The risk varies with species, muscle type, carcass temperature, and chilling conditions.
43. Prevention of Cold Shortening
Cold-shortening risk can be controlled through appropriate chilling rates, carcass-temperature management, electrical stimulation where appropriate, and validated post-slaughter handling procedures. No single temperature-time combination is universally applicable to all meats.
44. Thaw Rigor
Thaw rigor can occur when susceptible pre-rigor muscle is frozen before rigor mortis has developed and subsequently thawed. Severe contraction can occur during thawing, resulting in increased toughness and substantial fluid loss.
45. Freezing of Meat
Freezing preserves meat by reducing temperature and converting a substantial proportion of available water into ice, thereby slowing microbial growth and chemical and enzymatic reactions. Freezing does not sterilize meat.
46. Packaging of Meat
Fresh meat may be packaged using materials and atmospheres selected according to the desired shelf life, colour stability, microbial control, storage temperature, and distribution system. Common technologies include vacuum packaging, modified-atmosphere packaging, and oxygen-permeable overwraps.
47. Vacuum Packaging
Vacuum packaging removes most of the air from the package before sealing. Reduced oxygen can slow oxidative reactions and the growth of many aerobic microorganisms. Vacuum packaging must be combined with appropriate refrigeration and validated food-safety controls.
48. Modified-Atmosphere Packaging
Modified-atmosphere packaging (MAP) uses a selected gas mixture, commonly involving oxygen, carbon dioxide, and nitrogen, to influence meat colour, oxidation, microbial growth, and shelf life. The appropriate atmosphere depends on the specific meat product and intended storage conditions.
E. FISH AND POULTRY TECHNOLOGY
49. Fish as a Highly Perishable Food
Fish and other aquatic foods are highly perishable because of their high moisture content, active endogenous enzymes, susceptible lipids, and microbial activity. Rapid icing or chilling, hygienic handling, temperature control, and appropriate packaging are essential for maintaining quality and safety.
50. Poultry Meat
Poultry meat is obtained primarily from domesticated birds such as chickens, turkeys, ducks, and geese. Poultry muscle undergoes postmortem glycolysis, pH decline, rigor development, protein changes, and water-loss processes similar to those observed in other meat species. Safe poultry processing requires hygienic slaughter and dressing, effective chilling, prevention of cross-contamination, appropriate packaging, and continuous temperature control.
IMPORTANT SCIENTIFIC POINTS FOR MEAT, FISH AND POULTRY TECHNOLOGY
Meat quality cannot be explained by a single factor. Muscle structure, protein composition, connective tissue, fat distribution, glycogen reserves, postmortem glycolysis, pH decline, temperature, chilling rate, freezing and thawing, packaging, and storage conditions interact to determine the final quality of meat.
Numerical values such as muscle composition, ultimate pH, chilling temperature, freezing temperature, storage temperature, microbial limits, or processing times should not be treated as universal values. Appropriate values depend on the species, product, processing system, intended shelf life, and applicable food-safety standard.
International requirements also differ among jurisdictions. Codex Alimentarius provides international food-hygiene standards and codes of practice, while national authorities establish legally enforceable requirements. Relevant regulatory frameworks may include FSSAI in India, DFTQC and applicable Nepalese standards in Nepal, FDA/USDA and FSIS requirements in the United States, CFIA and Health Canada in Canada, EU legislation in the European Union, FSANZ in Australia and New Zealand, and UK food legislation in the United Kingdom.
For scientific and regulatory writing, meat, fish, and poultry technology should therefore distinguish between scientific principles, typical industry values, validated processing parameters, and legally binding requirements.