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Milk is a white liquid produced by the of . It is the primary source of for young mammals before they are able to other types of food. Early- milk contains , which carries the mother's to the baby and can reduce the risk of many in the baby. It also contains many other nutrients.

As an product, milk is during or soon after pregnancy and used as for humans. Worldwide, farms produced about 730 million tonnes of milk in 2011. is the world's largest producer and consumer of milk, yet neither exports nor imports milk. , the 's 28 member states, , and the are the world's largest exporters of milk and milk products. and are the world's largest importers of milk and milk products.

Throughout the world, there are more than 6 billion consumers of milk and milk products. Over 750 million people live within dairy farming households. Milk is a key contributor to improving nutrition and food security particularly in developing countries. Improvements in livestock and dairy technology offer significant promise in reducing and in the world.


Types of consumption
There are two distinct types of milk consumption: a natural source of nutrition for all infant mammals and a food product for humans of all ages that is derived from other animals.


Nutrition for infant mammals
In almost all mammals, milk is fed to through , either directly or by the milk to be stored and consumed later. The early milk from mammals is called . Colostrum contains that provide protection to the newborn baby as well as nutrients and growth factors. The makeup of the colostrum and the period of secretion varies from species to species. ξ1

For humans, the recommends exclusive breastfeeding for six months and breastfeeding in addition to other food for two years or more. The World Health Organization's infant feeding recommendation , based on "Global strategy on infant and young child feeding" (2002). Retrieved February 8, 2013. In some cultures it is common to breastfeed children for three to five years, and the period may be even longer.: When to Wean (Paywall, Questia) , October 1997. Retrieved February 8, 2013.

Fresh goats milk is sometimes substituted for breast milk. This risks the child developing imbalances, , , and a host of .


Food product for humans

In many cultures of the world, especially the Western world, humans continue to consume milk beyond infancy, using the milk of other animals (especially , and ) as a food product. Initially, the ability to digest milk was limited to children as adults did not produce , an enzyme necessary for digesting the in milk. Milk was therefore converted to , and other products to reduce the levels of lactose. Thousands of years ago, a chance mutation spread in human populations in Europe that enabled the . This allowed milk to be used as a new source of nutrition which could sustain populations when other food sources failed. Milk is processed into a variety of dairy products such as , , , , , and cheese. Modern industrial processes use milk to produce , , lactose, , , and many other food-additive and industrial products.

The sugar lactose is found only in milk, flowers, and a few tropical shrubs. The enzyme needed to digest lactose, lactase, reaches its highest levels in the small intestines after birth and then begins a slow decline unless milk is consumed regularly. ξ2 On the other hand, those groups who do continue to tolerate milk often have exercised great creativity in using the milk of , not only of cattle, but also sheep, goats, , , , and . The largest producer and consumer of cattle and buffalo milk in the world is .

Per capita consumption of cow's milk and cow's milk products in selected countries in 2005–2006
5.3
1.0
2.9
3.3
4.3
1.0
5.6
3.7
3.7
3.3


Terminology
The term milk is also used for white colored, non-animal beverages resembling milk in color and texture such as , , , and . In addition, a substance secreted by to feed their young is called and bears some resemblance to mammalian milk. ξ3 relates to milk and milk production, e.g. dairy products.


Evolution of lactation
The is thought to have been derived from apocrine skin glands. It has been suggested that the original function of (milk production) was keeping eggs moist. Much of the argument is based on (egg-laying mammals). The original adaptive significance of milk secretions may have been nutrition or immunological protection. This secretion gradually became more copious and accrued nutritional complexity over evolutionary time.


History
Humans first learned to regularly consume the milk of other mammals following the of animals during the referring to the period in Eurasian prehistory or the development of . This development occurred independently in several places around the world from as early as 9000–7000 BC in ξ4 to 3500–3000 BC in the Americas. ξ4 The most important dairy animals—cattle, sheep and goats—were first domesticated in Southwest Asia, although domestic cattle has been independently derived from wild populations several times since. Initially animals were kept for meat, and archaeologist has suggested that dairying, along with the exploitation of domestic animals for hair and labor, began much later in a separate in the 4th millennium BC. ξ5 Sherratt's model is not supported by recent findings, based on the analysis of residue in prehistoric pottery, that show that dairying was practiced in the early phases of agriculture in Southwest Asia, by at least the 7th millennium BC.

From Southwest Asia domestic dairy animals spread to Europe (beginning around 7000 BC but not reaching Britain and Scandinavia until after 4000 BC), ξ6 and (7000–5500 BC). ξ7 The first farmers in central Europe and Britain milked their animals. and economies, which rely predominantly or exclusively on domestic animals and their products rather than crop farming, were developed as European farmers moved into the in the 4th millennium BC, and subsequently spread across much of the . ξ8 Sheep and goats were introduced to Africa from Southwest Asia, but African cattle may have been independently domesticated around 7000–6000 BC. ξ9 Camels, domesticated in central Arabia in the 4th millennium BC, have also been used as a dairy animal in North Africa and the Arabian peninsula. The earliest Egyptian records of burn treatment describe burn dressings using milk from mothers of male babies. In the rest of the world (i.e., East and Southeast Asia, the Americas and Australia) milk and dairy products were historically not a large part of the diet, either because they remained populated by who did not keep animals or the local agricultural economies did not include domesticated dairy species. Milk consumption became common in these regions comparatively recently, as a consequence of European and political domination over much of the world in the last 500 years.

In the , milk was called the virtuous white liquor because alcoholic beverages were more reliable than water. ξ10

In 1863, French chemist and biologist invented pasteurization, a method of killing harmful bacteria in beverages and food products. "The History Of Milk", . Retrieved 13-8-2010.

In 1884, Doctor , an American inventor from New York, invented the first glass , called 'Thatcher's Common Sense Milk Jar', which was sealed with a waxed paper disk. Later, in 1932, plastic-coated paper milk cartons were introduced commercially as a consequence of their invention by Victor W. Farris.


Sources of milk
The females of all mammal species can by definition produce milk, but cow milk dominates commercial production. In 2011, FAO estimates 85% of all milk worldwide was produced from cows.

Human milk is not produced or distributed industrially or commercially; however, milk banks exist that allow for the collection of donated human milk and its redistribution to infants who may benefit from human milk for various reasons (premature neonates, babies with allergies, , etc.). Why Bank Milk? Human Milk Banking Association of North America

In the Western world, cow's milk is produced on an industrial scale and is by far the most commonly consumed form of milk. Commercial using equipment produces the vast majority of milk in . such as the have been bred selectively for increased milk production. About 90% of the dairy cows in the and 85% in are Holsteins. Other dairy cows in the United States include , , , , and (Dairy Shorthorn).


Sources aside from cows

Aside from , many kinds of provide milk used by humans for dairy products. These animals include , , , , , , , . The first four respectively produced about 11%, 2%, 1.4% and 0.2% of all milk worldwide in 2011.

In and , small also exist.

According to the US National Bison Association, (also called American buffalo) are not milked commercially; however, various sources report cows resulting from cross-breeding bison and domestic cattle are good milk producers, and have been used both during the European settlement of North America and during the development of commercial in the 1970s and 1980s.


Production worldwide
Top ten cow milk producers in 2010 Food and Agricultural commodities production – Cow milk, whole, fresh, FAOSTAT, Food And Agricultural Organization of the United Nations. faostat.fao.org. Retrieved on 1 August 2012. !Country !!Production
()
87,446,130
50,300,000
36,036,086
31,895,100
31,667,600
29,628,900
23,301,200
17,010,500
13,960,000
12,480,100
599,438,003
In 2010, the largest producer of milk and milk products was India followed by the United States, China, Germany, Brazil, and Russia. Dairy – World Markets and Trade (see Milk tables). USDA All European Union members together produced about 138 million tonnes of milk in 2011.Schultz, Madeline (April 2012) fluid milk profile. Iowa State University

Increasing affluence in , as well as increased promotion of milk and milk products, has led to a rise in milk consumption in developing countries in recent years. In turn, the opportunities presented by these growing markets have attracted investment by dairy firms. Nevertheless, in many countries production remains on a small scale and presents significant opportunities for diversification of income sources by small farmers.Henriksen, J. (2009) ftp://ftp.fao.org/docrep/fao/011/i0521e/i0521e00.pdf FAO Diversification Booklet Series 6, Rome Local milk collection centers, where milk is collected and chilled prior to being transferred to urban dairies, are a good example of where farmers have been able to work on a basis, particularly in countries such as .Sinha, O.P. (2007) Agro-industries characterization and appraisal: Dairy in India, FAO, Rome


Production yields
FAO reports Israel dairy farms are the most productive in the world, with an yield of 12,546 kg milk per cow per year. This survey over 2001 and 2007 was conducted by ICAR (International Committee for Animal Recording International Committee for Animal Recording) across 17 developed countries. The survey found that the average herd size in these developed countries increased from 74 to 99 cows per herd between 2001 to 2007. A dairy farm had an average of 19 cows per herd in Norway, and 337 in New Zealand. Annual milk production in the same period increased from 7,726 to 8,550 kg per cow in these developed countries. The lowest average production was in New Zealand at 3,974 kg per cow. The milk yield per cow depended on production systems, nutrition of the cows, and only to a minor extent different genetic potential of the animals. What the cow ate made the most impact on the production obtained. New Zealand cows with the lowest yield per year grazed all year, in contrast to Israel with the highest yield where the cows ate in barns with energy-rich mixed diet.

Top ten buffalo milk producers in 2010 Livestock Production statistics, FAOSTAT, Food And Agricultural Organization of the United Nations. faostat.fao.org. Retrieved on 1 August 2012. !Country !!Production
()
62,400,000
22,279,000
3,100,000
2,725,000
1,066,870
279,800
248,400
210,200
46,990
36,000
92,517,217
The milk yield per cow in the United States, the world's largest cow milk producer, was 9,954 kg per year in 2010. In contrast, the milk yields per cow in India and China – the second and third largest producers – were respectively 1,154 kg and 2,282 kg per year. FAOSTAT, Yield data 2010 – Cow milk, whole, fresh, FAOSTAT, Food And Agricultural Organization of the United Nations; faostat.fao.org; Retrieved on 1 August 2012.


Price
It was reported in 2007 that with increased worldwide prosperity and the competition of bio-fuel production for feed stocks, both the demand for and the price of milk had substantially increased worldwide. Particularly notable was the rapid increase of consumption of milk in China and the rise of the price of milk in the United States above the government subsidized price.Wayne Arnold, "A Thirst for Milk Bred by New Wealth Sends Prices Soaring", September 4, 2007. In 2010 the predicted farmers would receive an average of $1.35 per US gallon of cow's milk (35 cents per liter), which is down 30 cents per gallon from 2007 and below the point for many cattle farmers.


Grading
In the United States, there are two grades of milk, with Grade A primarily used for direct sales and consumption in stores, and Grade B used for indirect consumption, such as in cheese making or other processing.

The differences between the two grades are defined in the Wisconsin administrative code for Agriculture, Trade, and Consumer Protection, chapter 60. Wisconsin administrative code for Agriculture, Trade, and Consumer Protection, Chapter ATCP 60. (PDF) . Retrieved on 2011-11-24. Grade B generally refers to milk that is cooled in milk cans, which are immersed in a bath of cold flowing water that typically is drawn up from an underground water well rather than using mechanical refrigeration.


Physical and chemical properties of milk
Milk is an or of within a water-based fluid that contains dissolved carbohydrates and protein aggregates with minerals.Rolf Jost "Milk and Dairy Products" Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2002. Because it is produced as a food source for a neonate, all of its contents provide benefits to the growing young. The principal requirements of the neonate are energy (lipids, lactose, and protein), biosynthesis of non-essential amino acids supplied by proteins (essential amino acids and amino groups), essential fatty acids, vitamins and inorganic elements, and water.
(fat) derived from fatty acids such as , , and .]]


Lipids
Initially milk fat is secreted in the form of a fat globule surrounded by a membrane.Fox, P.F. Advanced Dairy Chemistry: Vol 2 Lipids. 2nd Ed. Chapman and Hall: New york, 1995. Each fat globule is composed almost entirely of triacylglycerols and is surrounded by a membrane consisting of complex lipids such as , along with proteins. These act as which keep the individual globules from coalescing and protect the contents of these globules from various in the fluid portion of the milk. Although 97–98% of lipids are triacylglycrols, small amounts of di- and monoacylglycerols, free cholesterol and cholesterol esters, free fatty acids, and phospholipids are also present. Unlike protein and carbohydrates, fat composition in milk varies widely in the composition due to genetic, lactational, and nutritional factor difference between different species.

Like composition, fat globules vary in size from less than 0.2 to about 15 micrometers in diameter between different species. Diameter may also vary between animals within a species and at different times within a milking of a single animal. In unhomogenized cow's milk, the fat globules have an average diameter of two to four and with homogenization, average around 0.4 micrometers. The vitamins , , , and along with essential fatty acids such as linoleic and linolenic acid are found within the milk fat portion of the milk.


Proteins
Normal bovine milk contains 30–35 grams of protein per liter of which about 80% is arranged in casein micelles.


Caseins
The largest structures in the fluid portion of the milk are : aggregates of several thousand protein molecules with superficial resemblance to a surfactant , bonded with the help of nanometer-scale particles of . Each casein micelle is roughly spherical and about a tenth of a micrometer across. There are four different types of casein proteins: αs1-, αs2-, β-, and κ-caseins. Collectively, they make up around 76–86%Fox, P. F. Advanced Dairy Chemistry, Vol. 3: Lactose, Water, Salts and Vitamins. 2nd ed. Chapman and Hall: New York, 1995. of the protein in milk, by weight. Most of the casein proteins are bound into the micelles. There are several competing theories regarding the precise structure of the micelles, but they share one important feature: the outermost layer consists of strands of one type of protein, , reaching out from the body of the micelle into the surrounding fluid. These kappa-casein molecules all have a negative and therefore repel each other, keeping the micelles separated under normal conditions and in a stable in the water-based surrounding fluid.

Milk contains dozens of other types of proteins beside the caseins including enzymes. These other proteins are more water-soluble than the caseins and do not form larger structures. Because the proteins remain suspended in the left behind when the caseins coagulate into curds, they are collectively known as whey proteins. Whey proteins make up approximately 20% of the protein in milk, by weight. is the most common whey protein by a large margin.


Salts, minerals, and vitamins
Minerals or milk salts, are traditional names for a variety of cations and anions within bovine milk. Calcium, phosphate, magnesium, sodium, potassium, citrate, and chlorine are all included as minerals and they typically occur at concentration of 5–40 mM. The milk salts strongly interact with casein, most notably calcium phosphate. It is present in excess and often, much greater excess of solubility of solid calcium phosphate. In addition to calcium, milk is a good source of many other vitamins. Vitamins A, B6, B12, C, D, K, E, thiamine, niacin, biotin, riboflavin, folates, and pantothenic acid are all present in milk.


Calcium phosphate structure
For many years the most accepted theory of the structure of a micelle was that it was composed of spherical casein aggregates, called submicelles, that were held together by calcium phosphate linkages. However, there are two recent models of the casein micelle that refute the distinct micellular structures within the micelle.

The first theory attributed to de Kruif and Holt, proposes that nanoclusters of calcium phosphate and the phosphopeptide fraction of beta-casein are the centerpiece to micellular structure. Specifically in this view, unstructured proteins organize around the calcium phosphate giving rise to their structure and thus no specific structure is formed.

The second theory proposed by Horne, the growth of calcium phosphate nanoclusters begins the process of micelle formation but is limited by binding phosphopeptide loop regions of the caseins. Once bound, protein-protein interactions are formed and polymerization occurs, in which K-casein is used as an end cap, to form micelles with trapped calcium phosphate nanoclusters.

Some sources indicate that the trapped calcium phosphate is in the form of Ca9(PO4)6; whereas, others say it is similar to the structure of the mineral brushite CaHPO4 -2H2O. chemistry and physics. Foodsci.uoguelph.ca. Retrieved on 2011-12-09.


Carbohydrates and miscellaneous contents
Milk contains several different including lactose, glucose, galactose, and other oligosaccharides. The gives milk its sweet taste and contributes approximately 40% of whole cow's milk's calories. Lactose is a disaccharide composite of two , and . Bovine milk averages 4.8% anhydrous lactose, which amounts to about 50% of the total solids of skimmed milk. Levels of lactose are dependant upon the type of milk as other carbohydrates can be present at higher concentrations that lactose in milks.

Other components found in raw cow's milk are living , mammary gland cells, various , and a large number of active .


Appearance
Both the fat globules and the smaller casein micelles, which are just large enough to deflect light, contribute to the opaque white color of milk. The fat globules contain some yellow-orange carotene, enough in some breeds (such as and ) to impart a golden or "creamy" hue to a glass of milk. The in the whey portion of milk has a greenish color, which sometimes can be discerned in skimmed milk or whey products. Fat-free skimmed milk has only the casein micelles to scatter light, and they tend to scatter shorter-wavelength blue light more than they do red, giving skimmed milk a bluish tint.


Processing
In most countries, centralized facilities process milk and products obtained from milk (), such as , , and . In the , these dairies usually are local companies, while in the facilities may be run by very large nationwide or trans-national corporations (such as ).


Pasteurization
is used to kill harmful by heating the milk for a short time and then immediately cooling it. The standard High Temperature Short Time (HTST) process produces a 99.999% reduction in the number of bacteria in milk, rendering it safe to drink for up to three weeks if continually refrigerated. Dairies print on each container, after which stores will remove any unsold milk from their shelves.

A side effect of the heating of pasteurization is that some vitamin and mineral content is lost. Soluble calcium and phosphorus decrease by 5%, thiamin and vitamin B12 by 10%, and vitamin C by 20%. Because losses are small in comparison to the large amount of the two B-vitamins present, milk continues to provide significant amounts of thiamin and vitamin B12. As milk is not an important dietary source of vitamin C, this loss is not nutritionally significant.

A newer process, ultrapasteurization or ultra-high temperature treatment (), heats the milk to a higher temperature for a shorter amount of time. This extends its and allows the milk to be stored unrefrigerated because of the longer lasting effect.


Microfiltration
is a process that partially replaces pasteurization and produces milk with fewer microorganisms and longer shelf life without a change in the taste of the milk. In this process, cream is separated from the whey and is pasteurized in the usual way, but the whey is forced through ceramic microfilters that trap 99.9% of microorganisms in the milk (as compared to 99.999% killing of microorganisms in standard ). The whey then is recombined with the pasteurized cream to reconstitute the original milk composition.


Creaming and homogenization
Upon standing for 12 to 24 hours, fresh milk has a tendency to separate into a high-fat layer on top of a larger, low-fat milk layer. The cream often is sold as a separate product with its own uses. Today the separation of the cream from the milk usually is accomplished rapidly in . The fat globules rise to the top of a container of milk because fat is less dense than water. The smaller the globules, the more other molecular-level forces prevent this from happening. In fact, the cream rises in cow's milk much more quickly than a simple model would predict: rather than isolated globules, the fat in the milk tends to form into clusters containing about a million globules, held together by a number of minor whey proteins. These clusters rise faster than individual globules can. The fat globules in milk from goats, sheep, and water buffalo do not form clusters as readily and are smaller to begin with, resulting in a slower separation of cream from these milks.

Milk often is , a treatment that prevents a cream layer from separating out of the milk. The milk is pumped at high pressures through very narrow tubes, breaking up the fat globules through and . A greater number of smaller particles possess more total than a smaller number of larger ones, and the original fat globule membranes cannot completely cover them. Casein micelles are attracted to the newly exposed fat surfaces. Nearly one-third of the micelles in the milk end up participating in this new membrane structure. The casein weighs down the globules and interferes with the clustering that accelerated separation. The exposed fat globules are vulnerable to certain present in milk, which could break down the fats and produce flavors. To prevent this, the enzymes are inactivated by pasteurizing the milk immediately before or during homogenization.

Homogenized milk tastes blander but feels creamier in the mouth than unhomogenized. It is whiter and more resistant to developing off flavors. Creamline (or cream-top) milk is unhomogenized. It may or may not have been pasteurized. Milk that has undergone high-pressure homogenization, sometimes labeled as "ultra-homogenized," has a longer shelf life than milk that has undergone ordinary homogenization at lower pressures. Homogenized milk may be more digestible than unhomogenized milk.

Kurt A. Oster, M.D., who worked during the 1960s through the 1980s, suggested a link between homogenized milk and , due to damage to resulting from the release of bovine (BXO) from the milk fat globular membrane (MFGM) during homogenization. Oster's hypothesis has been widely criticized, however, and has not been generally accepted by the scientific community. No link has been found between atherosclerosis and milk consumption.


Nutrition and health
The composition of milk differs widely among species. Factors such as the type of protein; the proportion of protein, fat, and sugar; the levels of various vitamins and minerals; and the size of the , and the strength of the are among those that may vary. For example:
  • contains, on average, 1.1% protein, 4.2% fat, 7.0% lactose (a sugar), and supplies 72 kcal of energy per 100 .
  • milk contains, on average, 3.4% protein, 3.6% fat, and 4.6% lactose, 0.7% and supplies 66 kcal of energy per 100 grams. See also further on.

Donkey and horse milk have the lowest fat content, while the milk of and may contain more than 50% fat.

Milk composition analysis, per 100 grams (Citing McCane, Widdowson, Scherz, Kloos, International Laboratory Services.) USDA National Nutrient Database for Standard Reference. Ars.usda.gov. Retrieved on 2011-11-24. ! Constituents ! Unit ! ! ! !
Waterg87.888.983.081.1
Proteing3.23.15.44.5
Fatg3.93.56.08.0
----Saturated fatty acidsg2.42.33.84.2
----Monounsaturated fatty acidsg1.10.81.51.7
----Polyunsaturated fatty acidsg0.10.10.30.2

Carbohydrate (i.e the sugar form of )g4.84.45.14.9
Cholesterolmg1410118
Calciummg120100170195
Energykcal666095110
kJ275253396463


Cow's milk
These compositions vary by breed, animal, and point in the lactation period.

Milk fat percentages !Cow breed !Approximate percentage
5.2
4.7
4.0
3.6

The protein range for these four breeds is 3.3% to 3.9%, while the lactose range is 4.7% to 4.9%.

Milk fat percentages may be manipulated by dairy farmers' stock diet formulation strategies. Mastitis infection can cause fat levels to decline. ξ11


Nutritional value
Processed cow's milk was formulated to contain differing amounts of fat during the 1950s. One cup (250 ml) of 2%-fat cow's milk contains 285 mg of , which represents 22% to 29% of the (DRI) of calcium for an adult. Depending on the age, milk contains 8  of , and a number of other nutrients (either naturally or through ) including:

The amount of from milk that is absorbed by the human body is disputed. Calcium from dairy products has a greater than calcium from certain vegetables, such as , that contain high levels of calcium- agents,Brody T. (1999) "Calcium and phosphate". pp. 761–94 in Nutritional biochemistry, 2nd ed. Boston: Academic Press, ISBN 0121348369. but a similar or lesser bioavailability than calcium from low-oxalate vegetables such as kale, broccoli, or other vegetables in the Brassica genus.


Recommended consumption
The U.S. federal government document Dietary Guidelines for Americans, 2010 Dietary Guidelines for Americans 2010, p. 38, U.S. Department of Agriculture, U.S. Department of Health and Human Services, December 2010. recommends consumption of 3 glasses of fat-free or low-fat milk for adults and children 9 and older (less for younger children). This recommendation is disputed by some health researchers who call for more study of the issue,Kotz, Deborah (2013-07-08) How much milk do we really need?. Boston Globe. given that there are other sources for calcium and vitamin D. The researchers also claim that the recommendations have been unduly influenced by the American dairy industry, and that whole milk may be better for health due to its increased ability to satiate hunger.


Medical research
A 2006 study found that for women desiring to have a child, those who consume full fat dairy products may slightly increase their fertility, while those consuming low-fat dairy products may slightly reduce their fertility.

Numerous studies have found that , found mainly in milk, meat and dairy products, provides several health benefits including prevention of atherosclerosis, different types of cancer, and hypertension and improved immune function.

There is recent evidence suggesting consumption of milk is effective at promoting muscle growth and improving post exercise muscle recovery.

In 2010, scientists at the identified a substance in dairy fat, trans-palmitoleic acid, that may substantially reduce the risk of type 2 diabetes. The researchers examined participants who have been followed for 20 years in an observational study to evaluate risk factors for cardiovascular diseases in older adults. During followup it was found that individuals with higher circulating levels of trans-palmitoleic acid had a much lower risk of developing diabetes, with about a 60% lower risk among participants in the highest quintile (fifth) of trans-palmitoleic acid levels. Component in common dairy foods may cut diabetes risk, study suggests. Sciencedaily.com (2010-12-23). Retrieved on 2011-01-14.


Lactose intolerance
, the sugar component of all milk, must be cleaved in the small intestine by the in order for its constituents, and , to be absorbed. The production of the enzyme lactase declines significantly after in all mammals. Consequently, many humans become unable to digest lactose properly as they mature. There is a great deal of variance, with some individuals reacting badly to even small amounts of lactose, some able to consume moderate quantities, and some able to consume large quantities of milk and other dairy products without problems. The gene in humans that controls lactase production, and hence lactose tolerance/intolerance, is labeled C/T-13910. An individual who consumes milk without producing sufficient lactase may suffer , , and , as the undigested lactose travels through the and serves as nourishment for intestinal that gas in processes known as and .

It is estimated that 30 to 50 million Americans are lactose intolerant, including 75% of Native Americans and African Americans, and 90% of Asian Americans. Lactose intolerance is less common among those descended from northern Europeans. Other genetic groups that have a lower prevalence of lactose intolerance are the of the Sahara, the of the West African Sahel, and the and of Sudan, as well as possibly the population of the Uganda–Rwanda area.Patterson, K. D. "Lactose Tolerance", The Cambridge World History of Food, Kiple, K.F. (Ed.) Cambridge University Press, 2000 Another locus of lactose tolerance is in Northern India.

Lactose intolerance is a natural process and there is no reliable way to prevent or reverse it.


Possible harms
Some studies suggest that milk consumption may increase the risk of suffering from certain health problems. Cow (CMA) is an immunologically mediated adverse reaction to one or more cow's milk proteins. Rarely is it severe enough to cause death.

Milk contains , a substance that breaks down in the human stomach to produce , an . In the early 1990s it was hypothesized that casomorphin can cause or aggravate , and are widely promoted. Studies supporting these claims have had significant flaws, and the data are inadequate to guide autism treatment recommendations.

A study demonstrated that men who drink a large amount of milk and consume dairy products were at a slightly increased risk of developing ; the effect for women was smaller. The reason behind this is not fully understood, and it also remains unclear why there is less of a risk for women. Several sources suggest a correlation between high calcium intake (2000 mg per day, or twice the US , equivalent to six or more glasses of milk per day) and . A large study specifically implicates dairy, i.e. low-fat milk and other dairy to which has been added.

A review published by the and the states that at least eleven human population studies have linked excessive dairy product consumption and prostate cancer.

Medical studies also have shown a possible link between milk consumption and the exacerbation of diseases such as , –mimicking symptoms in babies with existing cow's milk allergies, and the aggravation of Behçet's disease.


Flavored milk in US schools
Milk must be offered at every meal if a school district wishes to get reimbursement from the federal government. A quarter of the largest school districts in the US offer rice or soy milk and almost 17% of all US school districts offer lactose-free milk. Seventy-one percent of the milk served in US school cafeterias is flavored, causing some school districts to propose a ban because flavored milk has added sugars. (Though some flavored milk products use artificial sweeteners instead.) The Boulder, Colorado school district banned flavored milk in 2009 and instead installed a dispenser that keeps the milk colder.


Bovine growth hormone supplementation
Since November 1993, with FDA approval, Report on the Food and Drug Administration's Review of the Safety of Recombinant Bovine Somatotropin. Fda.gov. Retrieved on 2011-11-24. has been selling , also called rBGH, to dairy farmers. Cows produce bovine growth hormone naturally, but some producers administer an additional recombinant version of BGH which is produced through a because it increases milk production. Bovine growth hormone also stimulates liver production of . Monsanto has stated that both of these compounds are harmless given the levels found in milk and the effects of .

On June 9, 2006, the largest milk processor in the world and the two largest in the United States – , , and – announced that they are "on a nationwide search for rBGH-free milk." Milk from cows given rBST may be sold in the United States, and the FDA stated that no significant difference has been shown between milk derived from rBST-treated and that from non-rBST-treated cows. Voluntary Labeling of Milk and Milk Products From Cows That Have Not Been Treated With Recombinant Bovine Somatotropin. Fda.gov. Retrieved on 2011-11-24. Milk that advertises that it comes from cows not treated with rBST, is required to state this finding on its label.

Cows receiving rBGH supplements may more frequently contract an udder infection known as . Problems with mastitis have led to Canada, Australia, New Zealand, and Japan banning milk from rBST treated cows. Mastitis, among other diseases, may be responsible for the fact that levels of in milk vary naturally.

rBGH is also banned in the .


Criticism
and some other do not consume milk for reasons mostly related to and . They may object to features of including the necessity of keeping dairy cows pregnant, the killing of almost all the male offspring of dairy cows (either by disposal soon after birth, for production, or for ), the routine separation of mother and calf soon after birth, other perceived of , and of cows after their productive lives.

Some have criticized the American government's promotion of Milk consumption. The United States government administers the popular and milk mustache advertising campaigns, which cost roughly $180 million per year and make the milk industry millions of dollars. The main concern is the financial interest that the American government has taken in the dairy industry, promoting milk as the best source of calcium. All United States schools that are a part of the federally funded are required by the federal government to provide milk for all students. The Office of Dietary Supplements recommends that healthy adults between ages 19 and 50 get about 1,000 mg of calcium per day,United States. Office of Dietary Supplements. Dietary Supplement Fact Sheet: Calcium. 2013. Web. . but studies show that the human body can only retain about 550 mg of calcium per day. Milk also contains more excess calories, sugar, and fat than many other sources of calcium.

There is also some skepticism of the idea that large doses of calcium provide for healthier bones and teeth. This is a commonly held belief, but there have been some studies that show there is "no connection between the intake of calcium (in any form) and the reduced risk of bone fractures in women aged 34-71 years".Feskanich, D., WC Willett, MJ Stampfer, and GA Colditz. 1997. "Milk, dietary calcium, and bone fractures in women: a 12-year prospective study." American Journal of Public Health. Vol 87, Issue 6. 992-997 Another study suggests that calcium supplements do not contribute to bone gain when you surpass a daily intake of 800 mg.


Varieties and brands
Milk products are sold in a number of varieties based on types/degrees of
  • additives (e.g., vitamins),
  • age (e.g., cheddar),
  • coagulation (e.g., cottage cheese),
  • farming method (e.g., organic, grass-fed).
  • fat content (e.g., half and half),
  • fermentation (e.g., buttermilk),
  • flavoring (e.g., chocolate),
  • homogenization (e.g., cream top),
  • reduction or elimination of lactose,
  • mammal (e.g., cow, goat, sheep),
  • packaging (e.g., bottle),
  • pasteurization (e.g., raw milk),
  • water content (e.g., dry milk)

Milk preserved by the process does not need to be refrigerated before opening and has a longer shelf life than milk in ordinary packaging. It is typically sold unrefrigerated in the UK, US, Europe, Latin America, and Australia.


Reduction or elimination of lactose
Lactose-free milk can be produced by passing milk over lactase enzyme bound to an inert carrier. Once the molecule is cleaved, there are no lactose ill effects. Forms are available with reduced amounts of lactose (typically 30% of normal), and alternatively with nearly 0%. The only noticeable difference from regular milk is a slightly sweeter taste due to the generation of glucose by lactose cleavage. It does not, however, contain more glucose, and is nutritionally identical to regular milk.

, where approximately 17% of the Finnish-speaking population has hypolactasia, has had "HYLA" (acronym for hydrolysed lactose) products available for many years. Lactose of low-lactose level cow's milk products, ranging from ice cream to cheese, is enzymatically hydrolysed into glucose and galactose. The ultra-pasteurization process, combined with aseptic packaging, ensures a long shelf life. In 2001, launched a lactose-free milk drink that is not sweet like HYLA milk but has the fresh taste of ordinary milk. Valio patented the separation method to remove lactose. Valio also markets these products in , , , Zero Lactose – Enfin une solution pour les intolérants au lactose. Zerolactose.be. Retrieved on 2011-11-24. and the , where the company says is used. Lactose Free Milk. Real Goodness. Retrieved on 2011-11-24.

In the UK, where an estimated 15% of the population are affected by lactose intolerance, produces milk, cheese, and yogurt products that contain only 0.03% lactose.

To aid digestion in those with , milk with added bacterial cultures such as ("acidophilus milk") and ("") is available in some areas. "Yogurt and Other Cultured Dairy Products", National Dairy Council, 2000. Another milk with bacteria cultures ("") often is used in cooking to replace the traditional use of naturally , which has become rare due to the ubiquity of pasteurization, which also kills the naturally occurring Lactococcus bacteria. ξ12


Additives and flavoring
In areas where the cattle (and often the people) live indoors, commercially sold milk commonly has added to it to make up for lack of exposure to radiation.

Reduced-fat milks often have added to compensate for the loss of the vitamin during fat removal; in the this results in reduced fat milks having a higher vitamin A content than whole milk. "How to Buy Dairy Products", Home and Garden Bulletin 255, , February 1995. Retrieved 16 May 2007.

Milk often has added to it for better taste or as a means of improving sales. has been sold for many years and has been followed more recently by and others. Some nutritionists have criticized flavored milk for adding sugar, usually in the form of , to the diets of children who are already commonly obese in the US.


Distribution

Due to the short shelf life of normal milk, it used to be delivered to households daily in many countries; however, improved refrigeration at home, changing food shopping patterns because of supermarkets, and the higher cost of home delivery mean that daily deliveries by a are no longer available in most countries.


Australia and New Zealand
In and , prior to "metrification", milk was generally distributed in 1 pint (568ml) glass bottles. In Australia and in Ireland there was a government funded "free milk for school children" program, and milk was distributed at morning recess in 1/3 pint bottles. With the conversion to metric measures, the milk industry were concerned that the replacement of the pint bottles with 500ml bottles would result in a 13.6% drop in milk consumption; hence, all pint bottles were recalled and replaced by 600 mL bottles. With time, due to the steadily increasing cost of collecting, transporting, storing and cleaning glass bottles, they were replaced by cardboard cartons. A number of designs were used, including a tetrahedron which could be close-packed without waste space, and could not be knocked over accidentally. (slogan: No more crying over spilt milk.) However, the industry eventually settled on a design similar to that used in the United States. Milk and Juice Cartons Fact Sheet, Waste Wise WA, zerowastewa.com.au. Retrieved on 21 June 2009. Milk is now available in a variety of sizes in cardboard cartons (250 mL, 375 mL, 600 mL, 1 liter and 1.5 liters) and plastic bottles (1, 2 and 3 liters). A significant addition to the marketplace has been "long-life" milk (), generally available in 1 and 2 liter rectangular cardboard cartons. In urban and suburban areas where there is sufficient demand, home delivery is still available, though in suburban areas this is often 3 times per week rather than daily. Another significant and popular addition to the marketplace has been flavored milks – for example, as mentioned above, outsells in .


India
In rural , milk is home delivered, daily, by local milkmen carrying bulk quantities in a metal container, usually on a bicycle. In other parts of metropolitan , milk is usually bought or delivered in plastic bags or cartons via shops or supermarkets.


Pakistan
In , milk is supplied in jugs. Milk has been a staple food, especially among the pastoral tribes in this country.


United Kingdom
Since the late 1990s, milk-buying patterns have changed drastically in the . The classic , who travels his local (route) using a (often battery powered) during the early hours and delivers milk in 1 glass bottles with tops directly to households, has almost disappeared. The main reasons for the decline of UK home deliveries by milkmen are household refrigerators (which lessen the need for daily milk deliveries) and private car usage (which has increased supermarket shopping). In 1996, more than 2.5 billion liters of milk were still being delivered by milkmen, but by 2006 only 637 million liters (13% of milk consumed) was delivered by some 9,500 milkmen. By 2010, the estimated number of milkmen had dropped to 6,000. Assuming that delivery per milkman is the same as it was in 2006, this means milkmen deliveries now only account for 6–7% of all milk consumed by UK households (6.7 billion liters in 2008/2009).

Almost 95% of all milk in the UK is thus sold in shops today, most of it in plastic bottles of various sizes, but some also in . Milk is hardly ever sold in glass bottles in UK shops.


United States
In the United States, glass milk bottles have been replaced mostly with and plastic jugs. Gallons of milk are almost always sold in jugs, while half gallons and quarts may be found in both paper cartons and plastic jugs, and smaller sizes are almost always in cartons.

The "half pint" milk carton is the traditional unit as a component of school lunches, though some companies have replaced that unit size with a plastic bottle, which is also available at retail in 6- and 12-pack size.


Packaging
Glass milk bottles are now rare. Most people purchase milk in bags, plastic bottles, or plastic-coated paper cartons. (UV) light from can alter the flavor of milk, so many companies that once distributed milk in or highly containers are now using thicker materials that block the UV light. Milk comes in a variety of with local variants:
Distributed in a variety of sizes, most commonly in cartons for up to 1.5 liters, and plastic screw-top bottles beyond that with the following volumes; 1.1 L, 2 L, and 3 L. 1 liter are starting to appear in supermarkets, but have not yet proved popular. Most UHT-milk is packed in 1 or 2 liter paper containers with a sealed plastic spout.
Used to be sold in cooled 1 liter bags, just like in . Today the most common form is 1 liter aseptic cartons containing UHT skimmed, semi-skimmed or whole milk, although the plastic bags are still in use for pasteurized milk. Higher grades of pasteurized milk can be found in cartons or plastic bottles. Sizes other than 1 liter are rare.
1.33 liter plastic bags (sold as 4 liters in 3 bags) are widely available in some areas (especially the , and ), although the 4 liter plastic jug has supplanted them in . Other common packaging sizes are 2 liter, 1 liter, 500 mL, and 250 mL cartons, as well as 4 liter, 1 liter, 250 mL aseptic cartons and 500 mL plastic jugs.
Distributed most commonly in cartons for up to 1 liter, but smaller, snack-sized cartons are also popular. The most common flavors, besides the natural presentation, are chocolate, strawberry and vanilla.
Sweetened milk is a drink popular with students of all ages and is often sold in small plastic bags complete with straw. Adults not wishing to drink at a banquet often drink milk served from cartons or .
UHT milk ( trajno mlijeko/trajno mleko/трајно млеко) is sold in 500 mL and 1 L (sometimes also 200 ml) aseptic cartons. Non-UHT pasteurized milk ( svježe mlijeko/sveže mleko/свеже млеко) is most commonly sold in 1 L and 1.5 L PET bottles, though in Serbia one can still find milk in plastic bags.
Sizes of 500 mL, 1 liter (the most common), 1.5 liters, 2 liters and 3 liters are commonplace.
Commonly sold in 1 L or 1.5 L cartons, in some places also in 2 dl and 5 dl cartons.
Milk is sold in glass bottles (220 mL), cartons (236 mL and 1 L), plastic jugs (2 liters) and aseptic cartons (250 mL).
Commonly sold in 500 mL plastic bags and in bottles in some parts like in west. It is still customary to serve the milk boiled, despite pasteurization. Milk is often buffalo milk. Flavored milk is sold in most convenience stores in waxed cardboard containers. Convenience stores also sell many varieties of milk (such as flavored and ultra-pasteurized) in different sizes, usually in aseptic cartons.
Usually sold in 1 liter cartons, but smaller, snack-sized cartons are available.
Non-UHT milk is most commonly sold in 1 liter waxed cardboard boxes and 1 liter plastic bags. It may also be found in 0.5 L and 2 L waxed cardboard boxes, 2 L plastic jugs and 1 L plastic bottles. UHT milk is available in 1 liter (and less commonly also in 0.25 L) carton "bricks".
Commonly sold in 1 liter waxed paperboard cartons. In most city centers there is also of milk in glass jugs. As seen in , sweetened and flavored milk drinks are commonly seen in .
Sold in cartons (180 mL, 200 mL, 500 mL 900 mL, 1 L, 1.8 L, 2.3 L), plastic jugs (1 L and 1.8 L), aseptic cartons (180 mL and 200 mL) and plastic bags (1 L).
Milk is supplied in 500 mL Plastic bags and carried in Jugs from rural to cities and sell
Milk is supplied in 1000 mL Plastic bottles and delivered from factories to cities and sell
UHT milk is mostly sold in aseptic cartons (500 mL, 1 L, 2 L), and non-UHT in 1 L plastic bags or plastic bottles. Milk, UHT is commonly boiled, despite being pasteurized.
Commonly sold in 1 liter bags. The bag is then placed in a plastic jug and the corner cut off before the milk is poured.
Commonly sold in 0.3 L, 1 L or 1.5 L cartons and sometimes as plastic or glass milk bottles.
Commonly sold in 500 mL or 1L cartons or special plastic bottles. UHT milk is more popular. Milkmen also serve in smaller towns and villages.
Most stores stock sizes: 1 pint (568 mL, 2 pints (1.136 L), 4 pints (2.273 L), 6 pints (3.408 L) or a combination including both metric and imperial sizes. Glass milk bottles delivered to the doorstep by the milkman are typically pint-sized and are returned empty by the householder for repeated . Milk is sold at supermarkets in either aseptic cartons or HDPE bottles. Supermarkets have also now begun to introduce milk in bags, to be poured from a proprietary jug and nozzle.
Commonly sold in (3.78 L), half-gallon (1.89 L) and (0.94 L) containers of natural-colored HDPE resin, or, for sizes less than one gallon, cartons of waxed paperboard. Bottles made of opaque are also becoming commonplace for smaller, particularly metric, sizes such as one liter. The US single-serving size is usually the half-pint (about 240 mL). Less frequently, dairies deliver milk directly to consumers, from coolers filled with glass bottles which are typically half-gallon sized and returned for reuse. Some chains in the United States (such as in the ) sell milk in half-gallon bags, while another used for easy stacking in shipping and displaying is used by such as and , along with some stores.
Commonly sold in 1 liter bags. The bag is then placed in a plastic jug and the corner cut off before the milk is poured.

Practically everywhere, and evaporated milk are distributed in metal cans, 250 and 125 mL paper containers and 100 and 200 mL squeeze tubes, and (skim and whole) is distributed in boxes or bags.


Spoilage and fermented milk products
When is left standing for a while, it turns "". This is the result of , where ferment the in the milk into . Prolonged fermentation may render the milk unpleasant to consume. This fermentation process is exploited by the introduction of bacterial cultures (e.g. sp., sp., sp., etc.) to produce a variety of . The reduced pH from lactic acid accumulation denatures proteins and causes the milk to undergo a variety of different transformations in appearance and texture, ranging from an aggregate to smooth consistency. Some of these products include , , , , , , and . See for more information.

of cow's milk initially destroys any potential pathogens and increases the shelf life, but eventually results in spoilage that makes it unsuitable for consumption. This causes it to assume an , and the milk is deemed non-consumable due to unpleasant taste and an increased risk of . In raw milk, the presence of -producing bacteria, under suitable conditions, ferments the lactose present to lactic acid. The increasing in turn prevents the growth of other organisms, or slows their growth significantly. During pasteurization, however, these lactic acid bacteria are mostly destroyed.

In order to prevent spoilage, milk can be kept and stored between 1 and 4 degrees Celsius in . Most milk is pasteurized by heating briefly and then refrigerated to allow transport from to local markets. The spoilage of milk can be forestalled by using ultra-high temperature () treatment. Milk so treated can be stored unrefrigerated for several months until opened but has a characteristic "cooked" taste. , made by removing most of the water, can be stored in cans for many years, unrefrigerated, as can . The most durable form of milk is , which is produced from milk by removing almost all . The is usually less than 5% in both drum- and spray-dried powdered milk.

File:Milk in a Japanese supermarket.jpg|Refrigerated milk File:milk powder Incolac.jpg|Incolac powdered milk File:Iryska.png|A can of condensed milk File:Tin of condensed milk.jpg|An opened can of condensed milk File:Gezuckerte-Kondensmilch BMK.jpg|Condensed milk in a tube


Language and culture
The importance of milk in human culture is attested to by the numerous expressions embedded in our languages, for example, "the milk of human kindness". In ancient , the spilled her milk after refusing to feed , resulting in the .

In and , is traditionally made from fermented milk rather than cream. It can take several hours of churning to produce workable butter grains from fermented milk.Crawford et al., part B, section III, ch. 1: Butter. Retrieved 28 November 2005.

Holy books have also mentioned milk. The Bible contains references to the ''. In the , there is a request to wonder on milk as follows: 'And surely in the livestock there is a lesson for you, We give you to drink of that which is in their bellies from the midst of digested food and blood, pure milk palatable for the drinkers.'(16-The Honeybee, 66). The fast is traditionally broken with a glass of milk and dates.

is conducted by and priests, by pouring libations on the being worshipped, amidst the chanting of . Usually offerings such as milk, , , may be poured among other offerings depending on the type of abhishekam being performed.

To milk someone, in the vernacular of many English-speaking countries, is to take advantage of the person.

The word "milk" has had many slang meanings over time. In the 19th century, milk was used to describe a cheap alcoholic drink made from methylated spirits mixed with water. The word was also used to mean defraud, to be idle, to intercept telegrams addressed to someone else, and a weakling or 'milksop'. In the mid-1930s, the word was used in Australia meaning to siphon gas from a car. ξ13


Other uses
Besides serving as a beverage or source of food, milk has been described as used by farmers and gardeners as an organic and foliage fertilizer. Diluted milk solutions have been demonstrated to provide an effective method of preventing powdery mildew on grape vines, while showing it is unlikely to harm the plant.


See also


Bibliography
  • Dupuis, E. Melanie. Nature's Perfect Food (2002) excerpt and text search
  • Kardashian, Kirk. Milk Money: Cash, Cows, and the Death of the American Dairy Farm (2012) excerpt and text search
  • ξ2
  • Smith-Howard, Kendra. Pure and Modern Milk: An Environmental History Since 1900 (Oxford University Press; 2013) 229 pages; A study of milk control in the United States,
  • Valenze, Deborah. Milk: A Local and Global History (Yale University Press, 2011) 368 pp.
  • Wiley, Andrea. Re-imagining Milk: Cultural and Biological Perspectives (Routledge 2010) (Series for Creative Teaching and Learning in Anthropology) excerpt and text search
  • United States. Office of Dietary Supplements. Dietary Supplement Fact Sheet: Calcium. 2013. Web. .
  • Feskanich, D., WC Willett, MJ Stampfer, and GA Colditz. 1997. "Milk, dietary calcium, and bone fractures in women: a 12-year prospective study." American Journal of Public Health. Vol 87, Issue 6. 992-997


External links


References
    ^ (2018). 9780702027895, Saunders Elsevier.
    ^ (2018). 9780684800011, Scribner. .
    ^ (2018). 9781845930639, CABI Publishing.
    ^ (2018). 9780631205661, Blackwell Publushing.
    ^ (1981). 9780521227636, Cambridge University Press.
    ^ (2018). 9780521662031, Cambridge University Press.
    ^ (1996). 9781857285383, UCL Press.
    ^ (2018). 9780691058870, Princeton University Press.
    ^ (2018). 9781405101554, Blackwell Publishing.
    ^ (2018). 9780300117240, Yale University Press.
    ^ (1988). 9780309037952, National Academies Press. .
    ^ (1975). 9780672518317, Bobbs Merrill.
    ^ (2018). 9780304366361, Weidenfeld & Nicholson. .

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