Eating meat sometimes indicates that one is getting to the heart of the matter or finally getting down to the “meat of an issue.” Meat can also represent a bold and hearty grasp of the dreamer’s needs.
the skeletal musculature of slaughtered animals or game; for humans, one of the most important nutritional products. Meat is also composed of connective and fatty tissues, as well as an insignificant quantity of nerve tissue. Carcasses and parts of them (meat on bones) are also referred to as meat. Depending on the species of animal, meat may be called mutton or lamb, beef, or horsemeat, for example.
Chemical composition. Chemically, the muscle tissue of slaughtered animals is 73–77 percent moisture, 18–21 percent proteins, 1–3 percent lipids, 1.7–2 percent extractive nitrogenous substances, 0.9–1.2 percent extractive nitrogen-free substances, and 0.8–1.0 percent mineral substances. Myoglobin, the respiratory pigment in muscle, gives a freshly cut piece of meat its dark red color. Its derivative, oxymyoglobin, is responsible for the light red color that develops rapidly when meat is exposed to air. The nuclei of a muscle fiber consist chiefly of nucleoproteins. The myofibrils are made up of proteins of the actomyosin complex (about 60 percent of all proteins)—myosin, actin, and tropomyosin. The principal proteins in the connective tissue of meat are collagen and elastin, which are also components of the sarcolemma.
The extractive nitrogenous substances include carnosine, anserine, carnitine, phasphocreatine, creatine, creatinine, adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), inosine monophosphate (IMP), purine bases, amino acids, and urea. The nitrogen-free extractive substances include glycogen, glucose, hexose phosphates, and lactic and pyruvic acids.
The total lipid (fat) content of muscle tissue depends on the fatness of the animal. In muscle tissue (or lean meat) the level of phosphatides is fairly constant and fluctuates from 0.5 to 0.8 percent, depending on the type of meat. The total cholesterol content is 50–70 milligram percent (mg percent), and the total esterified cholesterol content, 3–5 mg percent. The triglyceride content varies greatly. Free fatty acids and monoglycerides and diglycerides are found in small quantities. Among the phosphatides in meat are lecithins, cephalins, sphingomyelins, and plasmalogens.
Most of the fatty acids (95–99 percent of the total content of fatty acids) of intramuscular lipids in slaughtered animals are higher fatty acids with an even number of carbon atoms. There are qualitative and quantitative differences in the composition of fatty acids in beef, pork, mutton, and lamb.
Lean meat contains 0.20–0.22 percent phosphorus, 0.32–0.35 percent potassium, 0.05–0.08 percent sodium, 0.020–0.022 percent magnesium, 0.010–0.012 percent calcium, 0.002–0.003 percent iron, 0.003–0.005 percent zinc, and many other trace elements, including copper, strontium, barium, boron, silicon, tin, lead, molybdenum, fluorine, iodine, manganese, cobalt, and nickel.
Biochemical processes after slaughter. Several hours after slaughter, rigor mortis begins to develop in muscle tissue. It is characterized by loss of flexibility and elasticity and by hardening of the muscles. When it is in a state of rigor mortis, meat is not suitable for use. Biochemical processes bring about the end of rigor mortis and cause the muscles to relax and soften.
The process that occurs after the death of the animal and that leads to significant improvement in the quality of the meat is called aging, a type of autolysis caused by the action of enzymes in the meat. In the meat industry, aging is promoted by keeping the carcasses in refrigeration chambers at 0°-4°C. Most of the biochemical reactions during aging involve the irreversible decomposition of certain cell components. Immediately after the animal’s death the decomposition of glycogen (glycogenolysis) begins. By a series of intermediate reactions, glycogen is converted into lactic acid, which plays an essential role in the aging of meat. Unless the meat contains sufficient glycogen, lactic acid will not form. If the animals are exhausted, ill, or excited before slaughter, their muscle tissue usually contains little glycogen, and they yield meat that is unstable in storage.
The principal changes in the nucleotides are dephosphorylation and deamination. The enzyme decomposition of ATP, which begins immediately after slaughter and ends 24 hours later, is accompanied by the accumulation of phosphoric acid and inosine monophosphate. Associated with these biochemical processes are physicochemical changes in meat proteins, which result in a significant change in the hydration of meat. Until the onset of rigor mortis, the meat of a freshly slaughtered animal retains water very well. During aging the meat becomes tender and juicy.
Flavor substances and other specific substances or their precursors, which, after culinary or technological processing, impart a characteristic flavor and aroma to a meat product, are formed during aging. The flavor of meat apparently depends on a number of water-soluble extractive substances, including inosinic acid, glutamic acid or its monosodium salt, free amino acids, and many other substances of low molecular weight. The flavor and aroma characteristic of different kinds of meat (beef, pork, mutton, or lamb) are due to lipids or compounds formed from these water-soluble substances. The optimal period for aging meat in a refrigeration chamber is 72 hours. When the storage period is increased (by up to ten days), the flavor, aroma, and tenderness of meat increase slowly.
Microbiological processes after slaughter. There are no microorganisms in healthy animals that are well rested before slaughter. Fatigue fosters the appearance of microorganisms from the intestinal tract in muscle tissue. The use of meat from fatigued animals or from animals that have been poorly fed for a long time may cause food poisoning. To increase the stability of meat and to protect it from the effects of microbes, a number of conditions are observed. The animals are given sufficient rest before slaughter, and the hide and hooves are cleaned. The carcass is bled thoroughly, dressed properly, and chilled rapidly. The temperature of the storage chamber is kept at 0°C, and the relative humidity at 85 percent.
During prolonged refrigeration (especially if the temperature regime is interrupted), the continuous increase in microorganisms on the meat’s surface usually results in sliming and putrefaction. The biochemistry of the processes that occur during putrefaction is fairly constant. Under the action of the enzymes of putrefactive microorganisms, proteins decompose, forming intermediate and end products of putrefaction, including malodorous ones (ammonia, hydrogen sulfide, carbon dioxide, mercaptans, skatole, indole, cresol, phenol, volatile fatty acids,
| Table 1. Protein and fat content and caloric value of the assimilable part of various meats | ||||
|---|---|---|---|---|
| Chemical composition of edible part (in percent) | Kilocalories1 per 100 g of edible part | |||
| Proteins | Fats | |||
| 1 1 kilocalorie = 4.19 kilojoules | ||||
| Mutton and lamb, Prime grade | ||||
| Refrigerated.......... | 13.9 | 16.0 | 206.0 | |
| Frozen | 15.0 | 17.0 | 220.0 | |
| Beef, prime grade.......... | ||||
| Refrigerated | 15.2 | 9.9 | 154.0 | |
| Frozen | 16.1 | 10.5 | 164.0 | |
| Pork, fatty............ | ||||
| Refrigerated............ | 12.2 | 35.6 | 381.0 | |
| Frozen................ | 12.8 | 36.1 | 388.0 | |
| Pork, lean.......... | ||||
| Refrigerated............ | 13.9 | 20.2 | 245.0 | |
| Frozen........... | 14.4 | 21.0 | 234.0 | |
| Veal, milk-fed........... | 16.1 | 7.0 | 131.0 | |
carbonyl compounds, amines, and alcohols, for example). Chemical methods of detecting spoilage are based on the chemistry of meat spoilage.
In the human diet, meat is a basic source of complete protein. It consists of valuable muscle proteins (myosin, actin, and globulin), which contain all the essential amino acids, and connective-tissue, incomplete proteins made up of collagen and elastin. When heated, collagen is converted to gluten (gelatin), which has biological value but does not contain the important amino acid tryptophan. Elastin, which does not soften even after prolonged cooking, has no nutritional value. The extractive nitrogenous substances, which are powerful stimulants to the digestive glands, are biologically the most active components of meat. Concentrated bouillons and roasted meat are very rich in these subtances. Because boiled meat contains few of them, it is used in dietotherapy. (See Table 1 for the content of proteins and fats in various meats.)
Because of the characteristic predominance of hard saturated fatty acids in them, meat fats have high melting points (beef fat, 45°-52°C; mutton and lamb fat, 45°-56°C; and pork fat, 34°-44°C). The assimilability of the fat depends on its melting point. Beef fat is 90 percent assimilable, and pork fat 97–98 percent.
Meat is also a source of some mineral substances and a number of trace elements, including copper, cobalt, and zinc. It also contains a good balance of the B vitamins (0.10–93 mg percent of thiamine [B1], 0.15–0.25 mg percent of riboflavin [B2], 2.7–6.21 mg percent of nicotinamide [vitamin PP], 0.3–0.61 mg percent of pyridoxine [B6], and 80–113 mg percent of choline).
K. S. PETROVSKII
Veterinary-sanitary appraisal. Appraisal of meat involves examination of animals before slaughter, as well as postmortem examination of the carcasses and organs. Only clinically healthy animals delivered from farms that are free of infectious diseases may be slaughtered for meat. These sanitary conditions are confirmed by veterinary certificates issued for each lot of cattle to be slaughtered. Each carcass and the organs from it undergo postmortem examination, which includes pathologicoanatomical, microbiological, and biochemical analysis. Organoleptic and physicochemical methods based on the chemistry of meat spoilage are used to evaluate freshness. In the early 1970’s histological analysis based on the detection of microstructural changes in stale meat was introduced. Meat is a perishable product that requires refrigeration and limitation of storage periods.
V. N. RUSAKOV