Milk
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Milk
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, foodmilk, liquid secreted by the mammary glands of female mammals as food for their young. The milk of the cow is most widely used by humans, but the milk of the mare, goat, ewe, buffalo, camel, ass, zebra, reindeer, llama, and yak is also used. The composition of milk varies with the species, breed, feed, and condition of the animal. Jersey and Guernsey cows produce milk of high butterfat content; Holsteins produce larger quantities of milk but with a lower butterfat content.
Milk prepared for sale is often homogenized; in this process it is pumped under pressure through small openings to break up the milk-fat globules, thus ensuring an equal distribution of fat throughout the milk rather than permitting it to rise to the top as cream. In most countries where milk is a commercial product, it is subject to regulations concerning its composition (i.e., the proportion of butterfat and other solids) and its purity, with sanitary measures in force that cover milk handlers, herds, plants, and equipment. Pasteurization (partial sterilization by heating) checks bacterial growth, thereby making milk safer to drink and increasing its keeping qualities and range of transport.
Milk, an almost complete food, consists of proteins (mainly casein), fat, salts, and milk sugar, or lactose, as well as vitamins A, C, D, certain B vitamins, and lesser amounts of others. (Many people are unable to digest milk after childhood because they stop producing an enzyme needed to break down lactose, but usually they still can digest yogurt, hard cheeses, and lactose-reduced milk products.) Commercial dairies often supplement natural vitamin D with a concentrate. Milk is a major source of calcium and a good source of phosphorus. Low-fat and skim milk fortified with vitamins A and D have the same nutritional value as whole milk, but with fewer calories and less cholesterol. Whole milk has 3.5% milkfat, low-fat milk 1% to 2%, and skim, 0.5%. Heavy cream has a minimum of 36% milkfat, half-and-half not less than 10.5% nor more than 18%.
A patent was issued for the production of dried milk in Great Britain in 1855, and for concentrated milk in the United States to Gail Borden in 1856. The two types of concentrated milk are condensed and evaporated; condensed milk is a sweetened product (over 40% sugar), and evaporated is unsweetened. Dried, or powdered, milk is made by passing a film of partially evaporated milk over a heated drum or by spraying it into a heated chamber in which the particles dry. Malted milk is a dried mixture made of milk and the liquid from a mash of barley malt and wheat flour.
The term milk is also applied to a number of plant-based drinks, such as soy milk, almond milk, coconut milk, or rice milk. Such drinks, which are mostly water, are produced using ground or grated seeds, grains, nuts, or the like that have been soaked in heated water for a period of time; the liquid, or milk, is produced by straining out and pressing the solids, and may be sweetened or flavored. Plant-based milks typically have less nutrients than animal milk, with soy milk being the most comparable, but commercial versions often have added nutrients.
See also butter; cheese; dairying; fermented milk.
Bibliography
See S. K. Kon, Milk and Milk Products in Human Nutrition (1972); T. Quinn, Dairy Farm Management (1980); D. Carrick, Milk (1985).
Milk
the fluid secreted by the mammary glands of mammals. It serves as food for a mammal’s young during the period after birth (lactation period). In the first days after birth, colostrum is secreted, which gradually becomes milk of the usual composition. Human milk contains all the nutrients needed by an infant. The caloric value of human milk is 65–70 kilocalories per 100 g, the pH is 6.9–7.5, and the density is 1.030–1.032 g/cm3. The chemical composition of the milk is 87.4 percent water, 0.91 percent casein, 1.23 percent albumin and globulin, 3.76 percent fat, 6.29 percent lactose, and 0.31 percent ash; human milk also contains some mineral salts and the vitamins A, B, C, and D.
The milk of agricultural animals is a valuable food product. Most milk destined for human consumption is from the cow. The milk of goats, sheep, mares, camels, asses, buffalo, zebus, yaks, and reindeer is used by humans on a more limited scale. Lactic-acid products, butter, and ice cream are made from the milk of agricultural animals. Milk contains water, proteins, fat, milk sugar (lactose), mineral substances (including trace elements), vitamins, enzymes, hormones, antibodies, gases, microorganisms, and pigments. Because milk consists of the optimal combination of these components, it is the most indispensable food product, particularly for children. It contains most of the elements needed for normal growth and development. The milk of different animals varies in chemical composition and nutritional value (see Table 1).
The proteins in milk consist primarily of casein, lactalbumin, and lactoglobulin. The production of cottage cheese and hard cheeses is based on casein’s tendency to coagulate under the action of enzymes. The albumin in milk plays an important role in ensuring growth processes; for example, globulin ensures the formation of antibodies. According to protein content, there are casein milks (cow, goat, and sheep) and albumin milks (mare, deer, and ass). The protein of casein milks consists of no less than 75 percent casein, and that of albumin milks consists of 50–65 percent albumin. In terms of biological properties, albumin milk is more valuable than casein milk.
The proteins of milk are among the most complete. They contain all of the necessary amino acids, including all the essential amino acids. The proportion among lysine, methionine, and tryptophan is particularly favorable in milk, and the sulfur-containing amino acids methionine and cystine—which are important in the prevention of atherosclerosis—are found in large quantity. Between 75 and 96 percent of milk proteins is assimilated by the body. Nitrogenous substances, such as urea, uric acid, creatinine, and riboflavin, are present in milk in small quantities (up to 0.05 percent).
The fat present in milk, or butterfat, is in the form of globules, measuring 0.5 to 20 microns in diameter (about 3 billion in 1 milliliter). Each globule is surrounded by a film containing extremely sparse complexes of phospholipids and trace elements. In milk that is allowed to stand undisturbed, the fat globules rise to the surface to form cream. Butterfat, which differs from other animal fats in its lower melting (27°–45°C) and freezing (between −17° and −21°C) points, distinctive flavor, and high assimilability, is used as a food product (creamery and clarified butter). Milk contains fatlike substances—phosphatides (lecithin and cephalin—which have important biological activities, including antisclerotic properties) and sterols (cholesterol and ergosterol).
The carbohydrate in milk, lactose, is present only in milk and readily undergoes various types of fermentation. It is used in the production of lactic-acid products, cheeses, and other dairy products. When there is a deficiency of the enzyme lactase in man, undecomposed milk sugar in the small intestine may become toxic. Mineral substances are found in milk in the form of salts of organic and inorganic acids. The ash in milk contains Ca, P, Na, K, Mg, S, and Cl. The chief constituents of the ash are Ca (125–130 mg/100 g) and P (95–105 mg/100 g).
Because milk has a high content of easily assimilated calcium, it is a particularly valuable food product; most other foods are low in calcium. The trace elements found in milk include Zn, Co, Cu, Mn, I, Fe, Al, Cr, Pb, Ti, and Ag. The value of the mineral content of milk lies in the balance of those elements that ensure normal development of skeletal and other systems, particularly in children. Milk contains most of the known vitamins; summer milk is particularly rich in vitamins. Milk also contains more than 60 enzymes, the most important of which are lactase, protease, lipase, amylase, and catalase. The enzymes promote digestion and play an important role in the conversion of milk into milk products. In addition, milk has hormones (oxytocin, prolactin, estrogen, epinephrine, insulin); antibodies, which promote immunity to disease (antitoxins, agglutinins, opsonins); gases (CO2, C2, H2, NH3); and microorganisms.
The normal microflora of milk includes milk molds, bacteria that produce lactic acid fermentation, and gas-forming bacteria. Some species that cause defects in milk are Bacillus coli, Bacillus subtilis, Proteus, and Micrococcus. To destroy the vegetative forms of microorganisms, including pathogenic microbes, milk is pasteurized or boiled; to destroy all microbes, milk is sterilized. When milk is first received, it contains antibacterial substances (lactenins) and, therefore, is bacteriostatic; that is, it inhibits propagation of bacteria. Because fresh milk remains bacteriostatic only for two or three hours, it is quickly chilled to a temperature lower than 8°C, so that it can be stored for about two days. Fresh milk has an acidity of 16°–18°T (degrees Turner). Milk sours at 28°–30°T and curdles at 65°–70°T.
In the USSR, pasteurized and sterilized milk for beverage purposes is produced. Pasteurized whole milk, standardized milk (with the standard fat content), reconstituted milk (from dry or condensed milk or cream), and vitamin fortified milk (100 mg of vitamin C per kg) have a standard for fat of 3.2 percent. Baked and extra-rich milk contain 6 percent fat, protein milk contains 1 percent fat, and nonfat milk contains almost no fat. The acidity of pasteurized milk is 20°–21°T (of protein milk, 25°T); the milk’s temperature when released from the dairy is 8°C, and its storage period is two or three days. Sterilized milk is produced with a fat content of 3.2 or 3.5 percent (in bottles and cartons); its storage period is ten days.
| Table 1. The chemical composition (in percentage) and the caloric content (in kilocalories* per 100 g) of various milks | |||||||
|---|---|---|---|---|---|---|---|
| Species | Dry substances | Fat | Protein | Lactose | Mineral substances | Caloric content | |
| Casein | Globulin and albumin | ||||||
| * 1 kilocalorie = 4.19 kilojoules | |||||||
| Cow | 13.0 | 3.9 | 2.7 | 0.5 | 4.7 | 0.7 | 69 |
| Buffalo | 17.9 | 7.7 | 3.8 | 0.7 | 4.8 | 0.8 | 110 |
| Zebu | 15.9 | 7.0 | 3.7 | 0.5 | 3.5 | 0.8 | 98 |
| Yak | 17.8 | 6.8 | 3.6 | 07 | 5.0 | 0.9 | 104 |
| Mare | 10.7 | 1.8 | 1.2 | 0.9 | 64 | 0.3 | 52 |
| Camel | 13.6 | 4.5 | 2.6 | 0.9 | 4.9 | 0.7 | 76 |
| Ass | 9.9 | 1.4 | 0.9 | 1.0 | 6.2 | 0.5 | 46 |
| Reindeer | 33.8 | 18.7 | 8.3 | 2.0 | 3.6 | 1.4 | 230 |
| Sheep | 18.5 | 7.2 | 4.5 | 1.2 | 4.6 | 0.9 | 109 |
| Goat | 13.4 | 4.3 | 3.0 | 0.6 | 4.5 | 0.8 | 73 |
| Hog | 16.0 | 4.6 | 6.0 | 1.2 | 3.1 | 1.1 | 85 |
| Rabbit | 30.6 | 10.5 | 13.5 | 2.0 | 2.0 | 2.6 | 170 |
| Dog | 23.0 | 9.3 | 4.1 | 5.6 | 3.1 | 0.9 | 141 |
| Cat | 17.8 | 3.3 | 3.1 | 6.0 | 4.9 | 0.5 | 91 |
| Dolphin | 51.2 | 43.7 | – | – | – | 0.5 | – |
| Whale | 37.6 | 22.2 | 8.2 | 3.8 | 1.8 | 1.7 | 264 |
According to data of the Nutrition Institute of the Academy of Sciences of the USSR, the daily milk requirement is 250–500 g for adults and 500–700 g for children. The production of milk on farms and its transport to and processing in dairies are under strict sanitary control. Dairies only accept milk from healthy animals that have been raised on farms where there are no cases of infectious diseases. Milk for the market (including milk for consumers’ cooperatives) must be certified by a meat-dairy and food-quality control station. Milk containing preservatives or additives or having flavor and odor defects is not certified. Dairies do not accept colostrum or milk obtained during the seven days before steaming up (fattening before parturition) the cows (old milk).
REFERENCES
Inikhov, G. S. Biokhimiia moloka i molochnykh produktov, 2nd ed. Moscow, 1962.Davidov, R. B., and V. M. Sokolovskii. Moloko i zdorov’e. Moscow, 1965.
Vesser, R. Tekhnologiia polucheniia i pererabotki moloka. Moscow, 1971. (Translated from French.)
Gigiena pitaniia, vol. 2. Moscow, 1971.
Davidov, R. B. Moloko i molochnoe delo, 4th ed. Moscow, 1973.
R. B. DAVIDOV and K. S. PETROVSKII
What does it mean when you dream about milk?
Milk is the elixir of life from mother to child. If the dreamer is receiving the milk, it can indicate that a deep inner nourishment is being received. Should the dreamer be giving the milk to one’s self or to another, much love and caring is being expressed in the dreamer’s life. Also, perhaps a caretaking profession is being sought.