Meat Technology Midterm PDF

GROSS STRUCTURE A meat animal possesses as many as 600 distinct muscles. Variations exist in respect of size and shape (triangular fan like or fusiform; long or short; broad or narrow) in the attachments (bones, cartilages, or ligaments); in blood or nerve supply; in association with...

GROSS STRUCTURE A meat animal possesses as many as 600 distinct muscles. Variations exist in respect of size and shape (triangular fan like or fusiform; long or short; broad or narrow) in the attachments (bones, cartilages, or ligaments); in blood or nerve supply; in association with other tissue; and in their action (fast, slow or intermittent) among muscles. These variations allow muscles to perform various type of movement ranging from gross as in the case of movement of limbs to very fine as in the case of eyes. However a basic structural pattern is common to every muscle, despite the variations listed above. Skeletal muscles are also known to as striated muscles as they appear as parallel striations of alternating light and dark bands. Muscles are composed of individual cells referred to as muscles fibres, which in turn is made up myofibrils, which in turn is composed of myofilaments. CONNECTIVE TISSUE ASSOCIATED WITH MUSCLE Muscles are composed of muscle fibre or muscle cells, the structural units of muscles.  A connective tissue sheath, referred to as epimysium is the outermost layer of every muscle. A finer connective tissue, referred to as perimysium emerge from the epimysium, penetrate the muscle, and divide muscle into muscle fibre bundles by aggregating muscle fibres, and cover the muscle fibre bundles. A finer connective tissue framework known as the endomysium, emanates from the perimysium and covers each individual muscles fibres. Connective tissue networks act as channels for passage of blood vessels and nerve fibres. Endomysium is an amorphous, non-fibrous sheath and is collagenous in nature. The collagenous fibres of the endomysium are associated with the cell membrane of the muscle fibre, sarcolemma by means of the basement membrane Sarcolemma is similar to plasmalemma of any other animal cell in respect of structure, composition and function and is endowed with great elasticity to endure the great distortion it undergoes during muscular contraction and relaxation. The sarcolemma, basement membrane and endomysium though closely associated, are distinct entities.  HISTOLOGICAL STRUCTURE - MYOFIBRE Muscle fibres, or muscle cells are long un-branched thread like multinucleate cells that taper slightly at both ends. Muscles fibres may attain the length of many centimetres though only rarely do they extend the entire length of a muscle as in the case of sartorius muscles, but is only about 10-100 µm in diameter. Invaginations of sarcolemma, referred to as transverse tubules or T system form a network of tubules and run along the entire length and around the entire circumference of the fibre. Motor nerve fibre endings terminate on invaginations of the sarcolemma at the myoneural junction. The structures present at the myoneural junction form a small mound on the surface of the muscles fibre. The entire complex is called motor end plate.  ORGANELLES OF THE MUSCLE FIBRE The cytoplasm of the muscle is called as sarcoplasm, in which, as is the case of any other cell, organelles and colloidal substances are suspended. Sacroplasm is composed of about 75- 80% water, and contain lipid droplets, glycogen granules, ribosome, numerous proteins, non-protein nitrogenous compounds and several inorganic constituents. The nuclei of the fibres are regularly distributed; about one every 5 µm, with increased numbers present at tendinous attachments and at myoneural junctions. Nuclei are located immediately beneath the sarcolemma in case of mammals, while they are centrally located in case of fishes. The nuclei are ellipsoidal in shape and their long axis is oriented parallel to the long axis of the fibre. The number and size of mitochondria in muscle fibres vary greatly. Mitochondria are relatively abundant at the periphery of the fibre near the poles of the nuclei and especially abundant at motor end plates. Mitochondria are located between myofibril, adjacent to Z disk, I bands or A – I junction (discussed below). Lysosomes are also present, as also are golgi bodies, plenty of which are found near the nuclei, though their total numbers are much less than in case of secretory cells. The endoplasmic reticulum is very well developed and is known as sarcoplasmic reticulum. Apart from these organelles, muscles fibres are principally composed of a unique organelle known as myofibrils. MYOFIBRILS Myofibrils are long thin, cylindrical rods, bathed by the sarcoplasm and usually 1-2 µm in diameter. A muscle fibre with a diameter of 50 µm from meat animals will have at least 1000 and could have as many as 2000 (or more) myofibrils. On microscopic examination, the myofibrils present an appearance of alternating light and dark bands.  A cross-section of myofibrils reveals a well-ordered array of dots of two distinct sizes. These dots are actually the myofilaments with different sizes corresponding to the thick andthin filaments of the myofibril. The thin filaments are almost all completely made up of a protein actin (actin filaments) , while the protein myosin (myosin filaments) is the sole constituent of the thick filaments. MYOFILAMENTS Areas of different density are visible within the light and dark bands of the myofibrils. The light band is singly refractive when viewed with polarized light, owing to the fact it exclusively contains actin filaments only, hence it is described as being isotropic and is called the I band. The broad dark band is doubly refractive when viewed with polarized light, as it contains both actin and myosin filaments, hence it is described as being anisotropic, and thus referred to as the A band. The ‘A’band is much denser than the ‘I’ band. Both the ‘A’ and ‘I’ bands are bisected by relatively thin lines. A dark thin band called the Z line bisects the ‘I’ band. A narrow dense band, known as the M line, bisects the centre of the ‘A’ band. The thick and the thin filaments differ in their dimensions, chemical composition, properties and position within the sarcomere. The thick filaments are approximately 14-16 nm (nanometres) in diameter (1 nm = one-billionth of a metre) and 1.5 µm long. The thick filaments constitute the ‘A’ band of the sarcomere. Since they consist almost entirely of protein myosin they are referred to as myosin filaments. They are held in transverse and longitudinal registers by thin cross bands located periodically along the length and by cross connections in the centre of the ‘A’ band. The alignment of these cross connections in the centre of the ‘A’ band corresponds to the transverse density characteristics of the M-line The thin filaments are about 6-8 nm in diameter and they extend approximately 1.0 µm on either side of the Z line. These filaments constitute I band of the sarcomere. They consist primarily of the protein actin and are referred to as the actin filaments. SMOOTH MUSCLE Smooth muscle is present in the greatest quantity in the walls of arteries, lymph vessels and in gastrointestinal and reproductive tracts. It is involuntary in nature. Smooth muscle fibres are long, unevenly thickened in the centre and tapering on both the sides. The myofibrils are homogenous and do not show alternating dark and light bands like those of skeletal muscle. There are no Z or M-lines.  The SR is also not much developed. Smooth muscle is poorly supplied with blood. CARDIAC MUSCLE Cardiac muscle possesses the unique property of rhythmic contractility, which continues from early embryonic life until death. Cardiac muscle has properties that resemble characteristic properties of both skeletal and smooth muscle. It is also involuntary. The muscle fibres are rounded to irregular in shape and give off branches, which get mixed up with those of nearby fibres. The nucleus is placed in the centre of the fibre. Myofibrils depict striations similar to skeletal muscle. The sarcoplasm shows numerous and much more mitochondria than the skeletal or smooth muscle. The intercalated discs are present at the position of Z-lines. GOLGI COMPLEX Golgi complex is located in the sarcoplasm near the nuclei. They consist of flattened vesicles, which apparently function as the “concentrating” and “packaging” apparatus for the products from the metabolic “production line” of the cell. The muscle fibre, being multinucleated, has numerous Golgi complexes. The vesicles of the Golgi complex resemble the membranes of the sarcoplasmic reticulum. PROTEINS OF THE MUSCLE Proteins of the muscle are classified based on their solubility characteristics as Sarcoplasmic proteins, which are soluble in water; Myofibrillar proteins, which are soluble in high ionic strength solutions and Connective tissue or Stromal proteins, which are insoluble in high ionic strength solutions, at low temperatures. Myofibrillar proteins, as the name indicates are associated with the myofibrils.  Myofibrillar proteins are further classified into Contractile proteins, Regulatory Proteins and Cytoskeletal proteins Contractile proteins as called so as they are involved in muscle contraction and the contractile proteins include actin and myosin. The proteins actin and myosin constitute approximately 65 percent of the protein in the myofibril. Regulatory proteins are so named because of their direct or indirect regulatory functions on the adenosine triphosphate-actin-myosin complex. The regulatory proteins include tropomyosin, troponin, two M proteins α-actinin, and β-actinin – listed in the decreasing order of concentration in the myofibril. The cytoskeletal proteins are involved maintaining the myofibrillar proteins in register and include titin, nebulin, C protein, M protein, desmin, filamentin, synemin and vinculin. Actin is a globular molecule about 5.5 µm in diameter. This is referred to as G-actin (for globular actin) and it constitutes the monomeric (single molecule) form of actin. o The fibrous nature of the actin filament is due to the longitudinal polymerization (linking) of G-actin monomers to form F-actin (fibrous actin). o In F-actin, the G-actin monomers are linked together in strands, similar to beads on a string. o Two strands of F-actin are spirally coiled around one another to form a “super helix “that is characteristic of the actin filament. o The isoelectric pH (pH of minimum electrical charge and solubility) of actin is approximately 4.7. o Actin possesses a relatively low charge. Myosin constitutes approximately 50-55 percent of the myofibrillar protein and is characterized by a high proportion of basic and acidic amino acids, making it a highly charged molecule. o The isoelectric pH of myosin is approximately 5.4. o Myosin, with lower proline content than actin, has a more fibrous nature. o The structure of the myosin molecule is an elongated rod shape, with a thickened portion at one end. o The thickened end of the myosin molecule is usually referred to as the head region and the long rod-like portion that forms the backbone of the thick filament is called thetail region. o The portion of the molecule between the head and the tail regions is called the neck. o The head region of the molecule is double headed and it projects laterally from the long axis of the filament. o When myosin is subjected to the proteolytic (protein breakdown) action of the enzyme trypsin, it is split near the neck into two fractions that differ in molecular weight;light meromyosin and heavy meromyosin.  In the centre of the ‘A’ band, on either side of the M line, the myosin filament contains the tail portion of the myosin molecules without any of the globular heads. This region within the H zone, on either side of the M line, is called the pseudo H zone. The polarity of the myosin filaments is such that the heads on either side of the bare central region of the A band are oriented at an oblique angle away from the M line. The protruding heads are the functionally active sites of the thick filaments during muscle contraction, since the myosin heads form cross bridges with actin filaments. During muscle contractions each myosin head attaches to a G-actin molecule of the actin filament. The formation of cross bridges through this interaction of actin and myosin filaments produces the chemical complex known as actomyosin. o The formation of actomyosin results in a rigid and relatively inextensible condition in the muscle. o Actomyosin is the major form of the myofibrillar proteins that is found in postmortem muscle and the rigidity associated with rigor mortis is largely due to this complex. o It is a transient compound in the living animal, since the cross bridges between the actin and myosin filaments are broken during the relaxation phase of the contraction cycle. (Cross bridges are almost nonexistent in muscle when it is at rest.) Tropomyosin constitutes 8-10 percent of the myofibrillar protein and like myosin, is highly charged molecule with a high content of acidic and basic amino acids. o The isoelectric point of tropomyosin occurs at a pH of about 5.1.  o Tropomyosin has a very low proline content, that contributes to its fibrous nature. o Tropomyosin molecules, consisting of two coiled peptide chains, attach end to end to one another and thus form long, thin filamentous strands. o In the actin filament, one such tropomyosin strand lies on the surface of each of the two-coiled chains of F-actin. o The tropomyosin strands lie alongside each groove of the actin super helix. o A single tropomyosin molecule extends the length of 7 G-actin molecules in the actin filament. Troponin, a globular protein with relatively high proline content, also constitutes 8-10 percent of the myofibrillar protein. o Like tropomyosin, troponin is present in the grooves of the actin filament where it lies astride the tropomyosin strands. o It is also probably present near the end of the tropomyosin molecules. o The troponin units shows a periodic repetitiveness along the length of the actin filament. o There is one molecule of troponin for every 7 or 8 G-actin molecules along the actin filament. o Troponin is a calcium-ion-receptive protein and calcium ion (Ca2+) sensitivity is its major function in the actomyosin-tropomyosin complex. α-actinin has proline content comparable to that of actin and it too is a globular molecule. o α-actinin is present in the Z line and constitutes about 2-2.5 percent of the myofibrillar protein. o It has been suggested that α-actinin functions as the cementing substance in the Z line.  Β-actinin, which is also a globular protein, is located at the ends of actin filaments and is believed to regulate their length by maintaining a constant length of about 1µm in each half sarcomere. o In the absence of β-actinin, actin filaments in vitro attain lengths of 3-4 µm or more. Sarcoplasmic proteins include all the enzymes involved in glycolysis, TCA cycle and also myoglobin, which is the pigment responsible for the colour of meat. Connective tissue proteins include collagen, reticulin and elastin. Z LINE ULTRA STRUCTURE In longitudinal section, an actin filament on one side of the Z line lies between two actin filaments on the opposite side of the Z line. This arrangement indicates that the actin filaments per se do not pass through the Z line. The actin filaments are believed to terminate at the Z line. Ultra-thin filaments, called Z filaments, constitute the material of the Z line and they connect with actin filaments on either side of it. Near the Z line, each actin filament connects to four Z filaments that pass obliquely through the Z line. Each of the four Z filaments then connects with an actin filament in the adjacent sarcomere. This structural arrangement of the Z line shows each actin filament of one sarcomere oriented in the centre of four actin filaments from the next sarcomere. In longitudinal sections, this offset (or oblique) arrangement of the Z filaments results in the characteristic zigzag pattern of the Z line and explains why an actin filament on one side of the Z line appears to lie between two actin filaments of the apposing sarcomere.  MYOFILAMENTS Areas of different density are visible within the light and dark bands of the myofibrils. The light band is singly refractive when viewed with polarized light, owing to the fact it exclusively contains actin filaments only, hence it is described as being isotropic and is called the I band. The broad dark band is doubly refractive when viewed with polarized light, as it contains both actin and myosin filaments, hence it is described as being anisotropic, and thus referred to as the A band. The ‘A’band is much denser than the ‘I’ band. Both the ‘A’ and ‘I’ bands are bisected by relatively thin lines. A dark thin band called the Z line bisects the ‘I’ band. A narrow dense band, known as the M line, bisects the centre of the ‘A’ band. The thick and the thin filaments differ in their dimensions, chemical composition, properties and position within the sarcomere. The thick filaments are approximately  14-16 nm (nanometres) in diameter (1 nm = one-billionth of a metre) and 1.5 µm long. The thick filaments constitute the ‘A’ band of the sarcomere. Since they consist almost entirely of protein myosin they are referred to as myosin filaments. They are held in transverse and longitudinal registers by thin cross bands located periodically along the length and by cross connections in the centre of the ‘A’ band. The alignment of these cross connections in the centre of the ‘A’ band corresponds to the transverse density characteristics of the M-line The thin filaments are about 6-8 nm in diameter and they extend approximately 1.0 µm on either side of the Z line. These filaments constitute I band of the sarcomere. They consist primarily of the protein actin and are referred to as the actin filaments. MYOFIBRILS Myofibrils are long thin, cylindrical rods, bathed by the sarcoplasm and usually 1-2 µm in diameter. A muscle fibre with a diameter of 50 µm from meat animals will have at least 1000 and could have as many as 2000 (or more) myofibrils. On microscopic examination, the myofibrils present an appearance of alternating light and dark bands. A cross-section of myofibrils reveals a well-ordered array of dots of two distinct sizes. These dots are actually the myofilaments with different sizes corresponding to the thick andthin filaments of the myofibril. The thin filaments are almost all completely made up of a protein actin (actin filaments) , while the protein myosin (myosin filaments) is the sole constituent of the thick filaments. In longitudinal section, the thick filaments are aligned parallel to each other and are arranged in exact alignment across the entire myofibril. Similarly, the thin filaments are exactly aligned across the myofibril, parallel to each other and to the thick filaments. This arrangement of the myofilaments, and the fact that the thick filaments overlap in certain regions along their longitudinal axes, accounts for the characteristic banding or striated appearance of the myofibril. This banding effect, which takes the form of alternate light and dark areas, explains the use of the term striated muscle to describe skeletal muscle. The long axis of myofibrils in most muscles and in all mammals is parallel to the length of the muscle and extends the entire length of the muscle fibre.  POSTMORTEM GLYCOLYSIS AND pH DECLINE In the absence of oxygen, anaerobic glycolysis leads to the formation of lactic acid from the glycogen reserves: The accumulation of lactic acid lowers down the muscle pH, which is an important postmortem change during the conversion of muscle to meat. The rate and extent of pH decline are variable, being influenced by the species of food animal, various preslaughter factors, environmental temperature, etc. In most species, a gradual decline continues from approximately pH 7 in the living muscle during first few hours (5-6 hours) and then there is a little drop in the next 15-20 hours, giving an ultimate pH in the range of 5.5 – 5.7. The rate of pH decline is enhanced at high environmental temperature. A low ultimate pH is desired to have a check on the proliferating microorganisms during storage. A sharp decline in postmortem pH even before the dissipation of body heat through carcass chilling may cause denaturation of muscle proteins. So, the muscles depict pale, soft and exudative (PSE) condition. Contrary to this, muscles which maintain a consistently high pH during postmortem conversion to meat due to depletion of glycogen prior to slaughter depicts a dark, firm and dry (DFD) condition. Both the conditions are undesirable.  RIGOR MORTIS It refers to stiffening of muscles after death and is another important postmortem change in the process of conversion of muscle to meat. It is now very well-known that a particular level or concentration of ATP complexed with Mg++ is required for breaking the actomyosin bond and bringing the muscle to a relaxed state and as it drops, permanent actomyosin crossbridges begin to form and muscle gradually becomes less and less extensible under an externally applied force. During the period immediately following exsanguination, the actomyosin formation proceeds very slowly at first and the muscle is relatively extensible and elastic. This period is called the delay phase of rigor mortis. Then actomyosin formation picks up and the muscle begins to loose extensibility. This phase is called the fast or onset phase of rigor mortis. When all the creatine phosphate (CP) is depleted, ADP can no longer be phosphorylated to ATP, muscle becomes quite inextensible and stiff. This stage marks the completion of rigor mortis is rapid. When postmortem pH decline is very slow or very fast, the onset and completion of rigor mortis is rapid. The onset of rigor mortis is enhanced at ambient temperature above 20°C. The phenomenon of rigor mortis resembles that of muscle contraction in a living animal muscle except that rigor mortis is irreversible under normal conditions. The resolution of rigor mortis takes place mainly due to proteolytic activity of lysosomal enzymes or microbial degradation of muscle structure in due course of time. Pre-rigor meat is quite tender but its toughness keeps on increasing until rigor mortis is completed. It continues to be tough for some more time. However, with the resolution of rigor due to denaturation or degradation or aging, meat becomes tender. The onset of rigor mortis is also accompanied by a decrease in water holding capacity. This is true even when rigor mortis takes place at a high pH due to disappearance of ATP and consequent formation of actomyosin. CONVERSION OF MUSCLE TO MEAT Meat is the post-rigor aspect of muscle and the conversion of 'Muscle' to 'Meat' is the result of series of biochemical biophysical changes initiated in muscle at the death of the animal due to stoppage of the blood circulation. The most immediate change caused due to bleeding is the cessation of the oxygen supply to the muscle resulting in inhibition of the cytochrome system & therefore, oxidative phosphorylation.  The sarcoplasmic ATPase depletes the ATP levels that increase the inorganic phosphate, which in turn stimulates the breakdown of glycogen to lactic acid. The ineffectual resynthesis of ATP by anaerobic glycolysis cannot maintain the ATP level and as it drops, actomyosin forms and the inextensibility of rigor mortis ensue. The loss of extensibility, which reflects actomyosin formation proceeds slowly at first (the delay period) then with great rapidity (the fast phase), extensibility then remains constant at low levels. The time to the onset of the fast phase of rigor at a given temperature depends most directly on the level of ATP. Synthesis of ATP from creatine phosphate and ADP or by glycolysis cannot maintain the ATP level for too long. Higher glycogen content of the muscle can prolong that time to some extent but not indefinitely. The onset of rigor is accompanied by a lowering in water holding capacity (WHC). This is not solely due to drop in pH and the consequent approach of the muscle proteins to their isoelectric point or due to denaturation of sarcoplasmic proteins. It has been shown that even when rigor mortis occurred at high pH, there was a loss of water holding due to the disappearance of ATP and to the consequent formation of actomyosin. The lowered ATP levels make it difficult to maintain the structural integrity of proteins. The lowering in pH, due to accumulation of lactic acid also makes liable to denature. Denaturation is accompanied by loss of power to bind water and the fall in pH causes the myofibrillar proteins approach their isoelectric point. Both events cause exudation. Denaturation of sarcoplasmic proteins also makes them liable to attack by cathepsin. The breakdown of proteins to peptide and amino acids and the accumulation of various metabolites from glycolytic and other processes afford a rich medium for bacteria. Resolution of rigor is a term used glibly to denote the decrease in tension generated in the muscle, during actinomyosin formation and muscle contraction. The resolution of rigor, is not on account breakdown of actinomyosin, but takes place due to decreasing tension, which is due to proteolytic degradation of specific myofibrillar proteins that lead to dissolution of Z discs, loss of ultrastructral integrity. Muscle, post the resolution of rigor is referred to as meat.  AGEING Ageing is the holding of carcasses just above its freezing point so as to obviate microbial spoilage, and this process is accompanied by an enhancement in tenderness and flavour of meat. The enhancement in flavour is mainly attributed to inosine(inosine monophosphate), a breakdown product of ATP(adenosine monophosphate). The breakdown of protein and fat during ageing resulting in formation of hydrogen sulphide, ammonia, actaldehyde, acetone, and di-acetyl and an increase in free amino acids also adds to the development of characteristic meat flavour. The improvement in tenderness is on account of the subtle proteolytis that take place in the cytoskeletal proteins. Calpains are causally responsible for the proteolysis associated with ageing, which brings about the tenderness associated with ageing Ageing period in different species of food animals o Cattle : 14 days o Sheep and Goats : 7 days o Pigs : 5 days o Chicken : 2 days Techniques commonly adopted to decrease ageing periods include electrical stimulation of carcasses (should be within half an hour of slaughter, to be effective); Calcium chloride infusion into carcasses or injection into meat INTRODUCTION Since muscle is the principal component of meat, a brief discussion of its composition is necessary. Like the animal body, muscle contains water, protein, fat, carbohydrate and inorganic constituents. Muscle contains approximately 75% water (range: 65- 80 %) by weight. Water is the principal constituent of the extracellular fluid and numerous chemical constituents are dissolved or suspended in it. Because of this it serves as the medium for the transport of substances between the vascular bed and muscle fibres. Proteins constitute 16-22 % of the muscle mass and are the principal component of the solid matter. Muscle proteins are generally categorized as sarcoplasmic, myofibrillar and stromal proteins based primarily upon their solubility.  The sarcoplasmic proteins are readily extractable in water or low ionic strength buffers (0.15 or less). However, the more fibrous of the myofibrillar proteins require intermediate to high ionic strength buffers for their extraction. The stromal proteins are comparatively insoluble. The sarcoplasmic proteins include myoglobin, hemoglobin and the enzymes associated with glycolysis, the citric acid cycle and the electron transport chain. Although the enzymes of the TCA cycle and the electron transport chain are contained within the mitochondria, they are readily extractable, along with those found directly in sarcoplasm. The myofibrillar proteins constitute the proteins associated with the thick and thin filaments. They include actin, myosin, tropomyosin, troponin, alpha - and beta - actinin, C protein and M proteins. These salt soluble proteins are required for emulsion stabilization in the manufacture of emulsion type sausage products. In addition to proteins, other nitrogenous compounds are present in muscle. They are categorized as nonprotein nitrogen (NPN) and include a host of chemical compounds. Notable among these are amino acids, simple peptides, creatine, creatine phosphate, creatinine, some vitamins, nucleosides and nucleotides including adenosine triphosphate (ATP). The lipid content of muscle is extremely variable, ranging from approximately 1.5 to 13 %. It consists primarily of the neutral lipids (triglycerides) and phospholipids. While some lipid is found intracellularly in muscle fibres, the bulk of it is present in the adipose tissue depots associated with the loose connective tissue septa between the bundles, the latter type of fat deposit is called Marbling or intramuscular fat. The carbohydrate content of the muscle tissue is generally quite small. Glycogen, the most abundant carbohydrate in the muscle, has an abundance that varies from approximately 0.5-1.3 % of the muscle’s weight. The bulk of the remainder of the carbohydrate is comprised of the mucopolysacharides associated with the connective tissues, glucose and other mono- or disaccharides and the intermediates of glycolytic metabolism. Finally, muscle contains numerous inorganic constituents notable among which are cations and anions of physiological significance, calcium, magnesium, potassium, sodium, iron, phosphorous, sulphur and chlorine. Many of other inorganic constituents found in the animal body are also present in muscle.  CHEMICAL COMPOSITION OF A TYPICAL ANIMAL MUSCLE Sl.No. COMPONENT PERCENT (WET BASIS) 1. Water (range 65 to 80) 75.0 2. Protein (range 16 to 22) 18.5 Myofibrillar Proteins 9.5 Myosin 5.0 Actin 2.0 Tropomyosin 0.8 Troponin 0.8 M protein 0.4 C protein 0.2 a -actinin 0.2 b -actinin 0.1 Sarcoplasmic Proteins 6.0 Soluble sarcoplasmic &mitochodrial 5.5 enzymes 0.3 Myoglobin 0.1 Hemoglobin 0.1 Cytochromes and flavoproteins 3.0 Stroma or Connective Tissue Proteins 1.5 Collagen and reticulin 0.1 Elastin 1.4 Other insoluble proteins 3. Lipids (variable range 1.5 to 3.0) 3.0 Neutral Lipids (range 0.5 to 1.5) 1.0 Phospholipids 1.0 Cerebrosides 0.5 Cholesterol 0.5 4. Non-protein Nitrogenous Substances 1.5 Creatine and Creatinine phosphate 0.5 Nucleotides o (Adenosine triphosphate (ATP), 0.3 o Adenosine dephosphate (ADP), etc.) Free Amino acids o Peptides (Anserine, carnosine, etc.) Other nonprotein substances [Creatinine, 0.3 urea, inosine monophosphate (IMP), nicotinamide adenine dinucleotide (NAD), 0.1 nicotinamide adenine dinucleotide phosphate (NADP)] 5. Carbohydrates and Non Nitrogenous 1.0 Substances (range 0.5 to 1.5) 0.8 Glycogen (variable range 0.5 to 1.3) 0.1 Glucose 0.1 Intermediates and products of cell metabolism (Hexose and triose phosphates, lactic acid, citric acid, fumaric acid, succinic acid, acetoacetic acid, etc) 6. Inorganic constituents 1.0 Potassium 0.3 Total phosphorus(Phosphates & inorganic phosphorus) 0.2 Sulphur (including sulphate) 0.2 Chlorine 0.1 Sodium 0.1 Others (Including magnesium, calcium, 0.1 iron, cobalt, copper, zinc, nickel, manganese, etc.)  MEAT FATS Meat fats contain ample amount of essential fatty acids (EFA) and the nutritional demand of EFA human beings is easily met by intramuscular fat itself. The calorific value of fat in meat is attributed to fatty acids in triglycerides. The number of calories from lean meat is frequently less than those derived from equal weights of many other foods. In fact, the calorific value of particular meat depends on the amount of fat in the meat cuts. The most important fatty acid in meat fat is oleic acid (mono unsaturated FA) followed by palmitic and stearic acids (saturated FA). The EFA in human diets are linoleic, linolenic, and arachidonic acids. Pork and organ meats are relatively good sources of linoleic and linolenic acids. It may be noted that excess dietary linoleic acid is converted to arachidonic acid in human body to meet its demand. The phospholipids are essential components of the cell wall as well as mitochondria and play a vital role in cellular metabolism. Meat fat always contains some quantity of cholesterol and blood cholesterol level increases after ingestion of cholesterol in food. However, dietary and serum cholesterol are not directly related. Organ meats have remarkable high cholesterol content as compared to skeletal meat. MINERALS In general, meat is a good source of all minerals except calcium. The minerals are in close association with lean tissues in meat. Of these, quantitatively potassium is most abundant followed by phosphorus. Meat is a good source of iron, which is required for the synthesis of haemoglobin, myoglobin and certain enzymes and thus plays a vital role in maintaining good health.  Since human body has a very limited capacity to store iron, mainly in liver, it has to be a part of regular dietary intake. Meat provides this important mineral in a form that is easily absorbed in the system. VITAMINS Lean meat is an excellent source of B-complex group of vitamins. Fat-soluble vitamin found in meat is associated with body fat. Vitamin C is almost absent in lean meat, although certain organs contain it in minor quantities. Among the B-complex group of vitamins thiamine, riboflavin and niacin are present in high concentrations. It may be noted that pork surpasses several meats with regard to B-complex vitamins are concerned. In fact, lean pork has 5-10 times more thiamine than other meats. It has been noted that in monogastric animals like pigs, intake of vitamins in feed is directly reflected in their tissues. Several organ meats have slightly less protein and fat than skeletal meats. However, these are quite often more economical sources of protein and vitamins than retail cuts of skeletal meats. Liver is a rich source of iron, riboflavin, niacin and vitamin.