Chemical Properties of Meat
Non-protein substances 3.5%
Water contributes to many of the characteristics of meat products.
Approximately 65% of the weight of fresh meat is from water which is directly related to the protein content of meat. There is a constant relationship of about 3.7 to 1 between water and protein content in fresh meat.
In all living animals, water contributes to cellular integrity, meaning it provides the internal pressure to keep cells from collapsing on themselves. Water also provides lubrication for muscle fibers, allowing smooth contraction and release of muscle tissue.
Protein binds with water in the cell because of a polar attraction between water and protein molecules. When an animal is slaughtered, the ability of the muscle to retain water is reduced. Postmortem changes will affect water loss in fresh meat. Several techniques are applied after slaughter to reduce water loss.
Postmortem is a term used to describe the state of the animal after it has been slaughtered. Once an animal has been slaughtered, rigor mortis, or the stiffening of body joints due to contraction of the muscle tissue, begins after a few hours. Rigor mortis occurs in a dead body because of the body’s inability to keep calcium ions out of the muscle cells.
Calcium ions promote the linking of actin and myosin, two types of muscle fibers, which begin to contract and are unable to release. The muscles will stay contracted until the muscle tissue begins to decompose, approximately 72 hours after death. Refrigeration and rapid cooling can delay the onset of rigor mortis, but the process will occur upon the thawing of the carcass. Meat is generally considered to be more tender if prepared after rigor mortis has passed.
Most of the reduction in water holding capacity of muscle is due to a decrease in the pH of the muscle. pH is a measurement of the acidity or alkalinity of a substance. The final water-binding ability depends on the rate and extent of the pH drop. When the pH drops rapidly during the conversion of muscle to meat (slaughtering), a lower water-binding capacity results.
The lowered pH is due to an accumulation of lactic acid, a product of glycogen metabolism, in the muscle of the animal. The lactic acid becomes concentrated in the muscle because the circulatory system, inactive after slaughtering, is unable to remove it.
As a source of protein, meat protein is the second largest component after the water one. Muscle protein is divided into 3 groups based on their solubility properties; firstly, sarcoplasmic protein (30%), myofibril protein (55%) and stromal protein or muscle tissue (15%).
Sarcoplasmic proteins are soluble in water and dilute salt solution contained in the sarcoplasmic. Myofibril protein is a protein-containing structures myofibril and is soluble in saline solution with a concentration of 1.5% or more. Stromal proteins are main constituent of connective tissue that is not soluble in salt solutions but soluble in alkali or acid treatment.Sarcoplasmic proteins include glyceraldehyde, aldose, enolase, creatine kinase, lactate dehydrogenase, pyruvate kinase, phosphorilase, myoglobin, calpain, chatepsin, extracellular proteins and membrane protein. Proteins are composed of myosin, actin, troponin, tropomyosin, M-protein, C-protein, Titin, Nebulin and Desmin. Myosin is the largest component in myofibril and dissolves into the solution with high ionic strength (greater than 0.3 M). Myosin has an important functional properties in meat, namely (a) is an enzyme with ATP-ase activity, (b) myosin form a complex with actin and (c) myosin form aggregate with each other to form filaments.
Stromal proteins include collagen, elastin and reticuline. This protein directly affects meat quality by:
- Lowering the tenderness of meat and it depends on the number of stromal protein and the degree of cross-linking other stromal proteins.
- Influencing meat emulsion capacity due to this protein is not soluble in water.
- Lowering Water Binding Capacity of meat because of the low content of hydrophilic and charged amino acids.
- Lowering meat nutritional value.
Muscle protein solubility is one of the factors influencing properties of water retention in the muscles and eventually affects meat quality. Physical and chemical bonding in muscle protein affects structural and texture muscle protein. There is a correlation between protein structure and solubility, and is related to tenderness or hardness of meat during processing and storage.
Other chemical components that are important in meat are fats. Although relatively few in amount, it is the 3rd largest chemical component in the flesh. Fat in meat has both beneficial and detrimental roles. One of the disadvantages is the oxidation. It affects meat processing. Fat is an important energy source because of the amount of energy produced can be doubled from that generated by proteins and carbohydrates. Fat in meat is generally in triglycerides form. The composition of triglycerides significantly determines meat tenderness and roughness. Fatty acid composition in each species is different and it is also has different effect on fat properties in each species. Total saturated fatty acids in sheep, cattle and pigs respectively 53%, 45% and 40%, while the unsaturated fatty acids respectively were 47%, 55% and 60%.
Soluble Non-Protein Organic Substances:
These substances fall into two categories: nitrogen-based substances such as free amino acids and vitamins, and carbohydrates such as lactic acid and glucose.
The major minerals consist of phosphorous and potassium together with small amounts of sodium, magnesium, calcium, zinc, and other trace metals. Thus meat is a good source of essential amino acids, minerals and vitamins, and a good source of energy (on average, beef yields 510 kJ and lamb yields 630 kJ per 100 g). All the essential amino acids required for life are present and highly bioavailable in raw muscle tissue. Iron, phosphorous and potassium (together with the sodium present in cured meats) are important minerals. Pork has a high vitamin B content, while liver is rich in a considerable number of vitamins, particularly vitamin A. Meat is an important dietary source of both vitamins B1 (thiamin) and B2 (riboflavin).
Physical Properties of Meat
- Water Activity Water Holding Capacity
- Meat Texture
- Odour And Flavor
- Principal component of meat.
- estimated close to 70 –75% (muscle is 65 to 85 %)
- Most variable component
- Most of the meats water is in the free state.
- Affects juiciness.
Water activity (Aw):
- Water activity (aw) is the term for the amount of free (not chemically or physically bound) water, which is available for the growth of microorganisms.
- This information is particularly important, as higher amounts of free water favour the growth of microorganisms, while lower amounts (drier products) result in less microbial growth.
- Bacteria usually require at least aw 0.91 and fungi at least aw 0.7
- This property affects odor, color, flavor, texture and shelf-life.
- The Aw is measured using a water activity meter.
- Typical aw in Meat Products
|Fresh meat||0.99 (0.99 to 0.98)|
|Raw-cooked sausages||0.97 (0.98 to 0.93)|
|Liver sausages||0.96 (0.97 to 0.95)|
|Dried meat||0.70 (0.90 to 0.60)|
Water Holding Capacity:
- The meats ability (myofibril protein) of retaining its water or added water, during the application of external forces such as cutting, grinding or pressing.
- Importance due to its influence on:
- Texture and firmness of raw meat
- Palatability characteristics
- Juiciness and tenderness of cooked meat
- Meat with high WHC will have a stronger structure and a dry texture.
- Conversely, if WHC is low then flesh is soft, moist texture/ watery and toughness of meat is lost.
- The most widely employed method for its determination is the filter-paper press technique.
- Texture is a degree of meat fineness or coarseness.
- Texture measurement can be visually, touched or chewed.
- Texture, hardness and structure of meat are influenced by several factors, including the WHC, rigor status, marbling fat, connective tissue content in meat and muscle bundle size.
- Meat with high WHC will have a stronger structure and a dry texture. Conversely, if WHC is low then flesh is soft, moist texture/ watery and toughness of meat is lost.
- Meat in pre rigor state has long sarcomere. When rigor, sarcomere shortened and peak rigor state, sarcomere lenght is very short. (The short sarcomere indicates that sarcomerer contract to form the actomyosin or cross bridge bond. The formation of this bond, meat becomes harder and stronger).
- The presence of fat marbling gives a soft texture. Low marbling content in meat marbling cause meat looks rough and dry. However, if excessive marbling produce meat with watery texture and it is also not good, Meat become soft and less rigid.
- Besides a role in texture, marbling fat also influence the aroma and juiceness meat. Fat marbling will give the distinctive aroma of meat and usually preferred by consumers.
- The proportion of high connective tissue that causes the coarse-textured meat and feels more hard and not soft.
Muscle Firmness or Wetness:
- Muscle firmness or wetness can be described as soft and exudative (SE), firm and normal (FN), or firm and dry (FD).
- Soft and exudative means that the meat does not hold its shape and that moisture drips from the meat. Soft and exudative meat is often drier and tougher when cooked, so it is less desirable to consumers; it does not work very well for processing into sausage products.
Soft and exudative meat is often associated with pale colored meat; this is known as PSE, or pale, soft and exudative meat.
- Both firm and normal and firm and dry meat are considered acceptable in the meat industry and to consumers.
Odour and Flavor:
- Meat odour and flavour depends on animal age, sex, the amount of fatty tissue and the nature of its distribution.
- Meat of previously sick, scraggy animal will always taste worse.
- Flavour of fresh meat is specific, somewhat sweetish.
- The pH of meat can range from 5.2 to 7.0.
- The highest quality products tend to fall in the pH range of 5.7 to 6.0.
- External appearance is characterized by overall appearance of a product or carcass meat.
- attention is paid to presence of mould on the surface, extraneous inserts and drawing of a cut (of products), drying of carcass meat.
- Bruising, clots, residues of skin and the internal organs not only impairs commercial appearance of meat but also decreases its durability for storing.
- Dependent on
- Pigment content
- Ultimate pH and rate of pH decline postmortem
- Nature of group attached to the iron and the state of the iron
- Ingredients, processing, packaging
- Two main pigments: myoglobin and hemoglobin
- Majority of color is due to myoglobin
- Amount of myoglobin in the muscle
- Age: Veal<Calf<Young beef<Old beef
- Looses affinity for oxygen as age increases
- Species: <Lamb<Beef
- Type: Support<Locomotive
Factors Affecting Meat Color
- Chemical State of Myoglobin
- Ferrous (Fe++)
- H2O→ Purple → Deoxymyoglobin
- O2 → Red → Oxymyoglobin
- NO → Unstable pink → Nitric oxide myobglobin
- CO → Red → Carboxymyoglobin
- Ferrous (Fe++)
- Vitamin E feeding of cattle
- Prevents oxidation; retards conversion of myoglobin to metmyoglobin
- Produce metmyoglobin, choleglobin, and sulfmyoglobin pigments
- Nitrosylhemochromogen is the stable cured meat pigment