Milk

Cow milk in a glass

Milk (Latin: lac) is an opaque whitish nutritive secretion produced by the secretory cells of the mammary glands of mammals, including monotremes. Its main function is to nourish the young until they are able to digest other foods, in addition to protecting their gastrointestinal tract against pathogens, toxins and inflammation and contributing to their metabolic health by regulating the processes of obtaining energy, in especially the metabolism of glucose and insulin. This ability is one of the defining characteristics of mammals. It is the only fluid ingested by young mammals (infants in the case of humans) until weaning. The milk secretion of a female in the days before and after giving birth is called colostrum.

The milk of some domestic mammals (mainly cows, but also buffaloes, sheep, goats, mare, camels, elks, sows, and others) are part of the normal human diet in some cultures, the basis of many dairy products, such as butter, cheese and yogurt, among others. The use of milk derivatives is very common in the agri-food, chemical and pharmaceutical industries, such as condensed milk, powdered milk, casein or milk. lactose. Cow's milk is also used in animal feed. It is mainly composed of water, ions (salt, minerals and calcium), carbohydrates (lactose), fat and proteins. There is evidence that, in addition, in the milk of almost all mammals (including humans) they can be formed by Casein breakdown bioactive peptides called casomorphins, which act as opioid receptor agonists, mimicking the biological effect of morphine. The assumption that one of them, β-casomorphin-7, is involved in the development of autism or cardiovascular diseases lacks scientific evidence. The milk of marine mammals, such as whales (for example), is much richer in fats and nutrients than that of terrestrial mammals.

A part of the population is intolerant to milk sugar (lactose). It can be of genetic origin (primary lactose intolerance) or due to diseases that damage the small intestine (secondary or acquired lactose intolerance). Anyone with genetic intolerance whose gut is healthy is able to consume at least 12 g of lactose at each meal (the amount contained in a cup of milk) without experiencing any or only mild symptoms. Consumption of dairy products by people with lactose intolerance does not cause damage to the gastrointestinal tract, but is limited to transient digestive discomfort. Reactions to smaller amounts of dairy are not explained by genetic intolerance, but rather indicate the existence of an undiagnosed intestinal disease (mainly celiac disease and non-celiac gluten sensitivity) or allergy to milk proteins. Labeling a person simply lactose intolerant without extensive testing including all the necessary medical tests, often causes long delays in the diagnosis of serious underlying diseases, causing malabsorption. n lactose, the most frequent celiac disease.

History

Human consumption of milk of animal origin began about eleven thousand years ago with the domestication of cattle during the so-called climatic optimum. This process occurred especially in the Middle East, prompting the Neolithic revolution. The first animal to be domesticated was the cow, starting with the aurochs, then the goat, at approximately the same dates, and finally the sheep, between 9,000 and 8,000 AD. a. C. There are hypotheses, such as the thrifty genotype, which state that this entailed a fundamental change in the eating habits of hunter-gatherer populations, who went from eating abundant, but sporadic, meals to receiving daily contributions of carbohydrates. According to this theory, this change made Eurasian populations more resistant to type 2 diabetes and more tolerant of lactose compared to other human populations that were only more recently introduced to livestock products. However, this hypothesis could not be verified and even its own author, James V. Neel, has refuted it, alleging that the differences observed in human populations could be due to other environmental factors.

Regarding the ability of adults to tolerate unfermented dairy products, especially milk, several hypotheses have been put forward. One of them is that the gene responsible for lactase (enzyme that hydrolyzes lactose), a rare and infrequent gene in Neolithic European populations, has possibly been preserved as a consequence of including dairy products. in human nutrition. It would have appeared 7,500 years ago in an area centered around present-day Hungary, and although this gene would compensate for the deficient synthesis of vitamin D in northern latitudes, this does not seem to be an essential factor for its appearance.

During the Ancient Ages and the Middle Ages, milk was very difficult to preserve and, for this reason, it was consumed fresh or in the form of cheeses. Over time other dairy products such as butter were added. The industrial revolution in Europe, around 1830, brought the possibility of transporting fresh milk from rural areas to large cities thanks to improvements in transportation. Likewise, new instruments have been appearing in the milk processing industry. One of the best known is pasteurization, first suggested for milk in 1886 by the German agricultural chemist Franz von Soxhlet. These innovations have resulted in healthier looking milk, more predictable shelf life and more hygienic processing.

Biology of milk

The mammal Eomaia It was a common ancestor of mammals and it is believed that it had the ability to produce milk like mammals today.

The production of milk to nourish the young could be an evolutionary trait associated with the hormone prolactin. Some species of fish in the genus Symphysodon are known to nourish their young with a milk-like fluid.

The so-called «crop milk» is present in various groups of birds, such as pigeons, flamingos or penguins. From a biological point of view, it is a true milk, secreted by specialized glands.

However, it is in mammals where this evolutionary adaptation becomes characteristic. It is believed that these come from a group close to the tritelodontids of the late Triassic period. These same sources believe that they already showed signs of lactation.

Among the many existing theories, it has been proposed that milk production arose because the synapsid ancestors of mammals had soft-shelled eggs, like modern monotremes, which caused them to dry out quickly. The milk would thus be a modification of the secretion of the sweat glands destined to transfer water to the eggs. Other authors, in a theory that may be complementary to the previous one, believe that the mammary glands come from the innate immune system and that lactation would be, in part, an inflammatory response to tissue damage and infection. Although there are difficulties, several approaches approximate the date of appearance in evolutionary history:

The evolutionary need to feed the babies is satisfied in the production of milk from the mammals.

• First, casein has a function, behavior and even structural motives similar to vitelogenin. The caseine appeared between 200 and 310 ma. It is observed that although in monotremas there is still this protein, it was gradually replaced by casein, allowing a smaller size of the eggs and finally its intrauterine retention.
• On the other hand, anatomical modifications are observed in advanced cynodontics that are only explained by the appearance of breastfeeding, such as small body size, epipubic bones and low dental replacement level.

The oldest fossil of placental mammals discovered to date is Eomaia scansoria, a small animal that outwardly resembled modern rodents and lived 125 million years ago during the Cretaceous period. It is almost certain that this animal produced milk like modern placental mammals.

Genetics, histology and cytology

Histological preparation of a human breast gland dyed with Eag 1.

The genetics of milk deals, on the one hand, with describing the genes involved in its biosynthesis, as well as its regulation and, on the other, with the selection of breeds or individuals or their genetic modification to increase production, quality or utilities. Zootechnics also deals with the latter.

Regulation

Milk production is regulated by lactogenic hormones (insulin, prolactin, and glucocorticoids), cytokines, and growth factors, and by substrate. These activate transcription factors, such as Stat5 (activated by prolactin). Several target sequences for these factors have been identified, such as the above and also for BLGe-1, OCT-1, C/EBP, Gr, Ets-1, YY1, Factor 5, Ying Yang 1, and CCAAT promoter binding protein.. These elements are usually located at a variable distance, depending on the species (in human calcium-sensitive caseins it is one of the most distant from the origin of transcription, at –4700/ –4550 nucleotides) and gather in groups (clusters). that contain both negative and positive elements, being regulated by combinations of factors, hence the great variability in the regulation of each protein. For example, the caseins appear to be regulated independently of each other. (Fox and McSweeney, 2003) Transcripts (mRNA) of milk proteins make up 60-80% of all the RNA present in an epithelial cell during lactation.

Genomic

Gene regulatory networks in milk production are not yet well understood. From a study carried out using microarrays, cell localization, interprotein interactions and gene data mining in the literature, some general conclusions have been drawn:

• About one third of the transcriptome is involved in the construction, operation and disassembly of the lactation apparatus.
• The genes involved in the secretion apparatus are transcribed before breastfeeding.
• All endogenous transcripts derive from less than 100 genes.
• While some genes are transcribed characteristically near the start of breastfeeding, this start is mediated mainly in post-transcriptional form.
• The secretion of materials during breastfeeding occurs not by overregulation of new genomic functions, but by widespread transcriptional deletion of functions such as protein degradation and cell-environmental communications.

Cytology

Milk-secreting epithelial cells actively separate materials from surrounding blood vessels, at what has been called the “mammary barrier” (in analogy to the blood-brain barrier). Once the barrier is crossed, the cells obtain the precursors they need to manufacture milk through their basal and basolateral membranes, which would be: ions, glucose, fatty acids and amino acids. In ruminants, acetate and β-hydroxybutyrate are also used as precursors. Some proteins, especially immunoglobulins, can also cross this barrier. Milk is expelled through the apical membrane. Milk lipids are synthesized in the smooth endoplasmic reticulum, while casein must mature in the Golgi apparatus, where lactose biosynthesis also takes place.

Histology

Histologically, milk is produced in the mammary glands, which are an evolution by hypertrophy of the hair-associated apocrine sweat glands, which is still evident in platypuses. The active mammary gland is composed of by lobules, each of which has numerous lobules and these in turn small alveoli with high or low cylindrical epithelial cells, depending on the activity cycle, which are responsible for producing milk. Between these and the basal lamina of the alveolus are some stellate myoepithelial cells. The epithelium of the ducts between the lobules is a prominent example of cuboidal bistratified epithelium (Bloom-Fawcet, 1999).

Definition and obtaining

Structure of a human breast gland during breastfeeding: 1-Grase, 2-Lóbulo lactiferous duct, 3-Lóbulo, 4-Conective woven, 5-Seno lactiferous duct, 6-Lactiferous duct.

Milk can be defined from the following points of view:

• Biological: is a substance segregated by the female of mammals in order to nourish the young.
• Legal: product of milking of a healthy mammal that does not represent a danger to human consumption.
• Technical or physical-chemical: system in balance, consisting of three scattered systems: solution, emulsion and suspension.

Milk Producing Animals

Currently, the milk most used in the production of dairy derivatives is cow's (due to the properties it possesses, the amount obtained, pleasant flavor, easy digestion, as well as the large number of derivatives obtained). However, it is not the only one that is exploited. There is also goat's milk, donkey, mare, camel, among others. The consumption of certain types of milk depends on the region and the type of animals available. Goat's milk is ideal for making dulce de leche (also called cajeta) and in arctic regions whale's milk is used. Donkey and mare milk contain less fat, while seal milk contains more than 50% of that.

Milk of human origin is not produced or distributed on an industrial scale. However, it can be obtained through donations. There are milk banks that are responsible for collecting it to provide it to premature or allergic children who cannot receive it in any other way. Worldwide, there are several species of animals from which milk can be obtained: sheep, goats, mare, donkey, camel (and other camelids, such as llama or alpaca), yak, buffalo, the female reindeer and the elk.

Milk from cows (Bos primigenius taurus) is the most important for the human diet and the one with the most industrial applications.

The cow milk of the Holstein breed is the one used most often in dairy farms.

• La European and Indica cow (Bos primigenius taurus) began to domesticate 11 000 years ago with two different mother lines, one for European cows and one for the Indicas. The ancestor of the current Bos taurus is called Bos primigenius. It was a bovine of broad horns that was domesticated in the Middle East, expanded by Africa, and led to the famous cebu race of Central Asia. Cebu is valued for its meat supply and milk. The European variant Bos primigenius has the shortest horns and is adapted for cattle breeding in stables. It is the one that has ended up giving a greater set of dairy breeds such as Holstein, Guernsey, Jersey, etc.

• The buffalo: The so-called water buffalo (Bubalus bubalis) was domesticated in 3000 BC in Mesopotamia. This animal is very sensitive to heat and its name denotes the habit of getting into the water to protect itself from it. In general, it is little known in the West. The Arabs brought him to the Middle East during the Middle Ages (700 BC). His employment in certain areas of Europe dates back to that time. For example, in the elaboration of the famous Italian buffalo mozzarella. Products made with buffalo milk begin to replace in some communities with cow milk.

• The yak, scientifically called Bos grunniens, it is a long-haired bovine that contributes fundamentally to the feeding of the populations of Tibet and Central Asia. It has a milk rich in proteins and fats (its concentration is superior to its void equivalent). Tibetans produce with it butter and different fermented dairy products. One of the best known is salt butter tea.

The mythological god Zeus milking the Amaltea goat.

• La sheep was domesticated in the Mediterranean, mainly from Ovis aries. From archaeological evidence, five mitochondrial lines produced between 9000 and 8000 BC have been identified. Bean milk is richer in fat content than buffalo milk and is even richer in protein content. It is highly valued in Mediterranean cultures.

• La goat began to domesticate mainly in the valley of Euphrates and the Zagros mountains from Capra aegagrus approximately at the same time as cows (about 10 500 years ago). It has a milk with a strong taste and aroma. Caprine milk is somewhat different from that of the sheep, mainly in terms of the flavor, and contains a greater amount of chlorides that give it a slightly salty taste. It is also more “gross” in cream content (caseinates), and has higher levels of calcium. The fatty matter of this milk is made of goat cheese.

• The Camel He is a relative far from the vaults and the oppressed (horses and sheep). It was domesticated in 2500 BC in Central Asia. Its milk is very appreciated in the arid climates where some cultures constantly use it, such as in the Northwest African gastronomy.

• La flame and the alpaca they are common animals in the Andean mountain range in South America. Its dairy production is mainly directed at local consumption and has no greater industrial projection.

• Vegetables: In various populations near the Arctic, the consumption of cérvide milk, such as reindeer, is frequent (Rangifer tarandus) and the elk (Alps.). The latter is sold in Russia and Sweden. Some studies suggest that children may be protected from gastrointestinal diseases.

• Equid: The production of mare milk is very important for many populations of the steppes of Central Asia, especially for the production of a fermented derivative called kumis, since raw consumption has a powerful laxative effect. This milk has a higher content of glucids than that of goat or cow and is therefore more suitable for alcoholic fermentation. It is estimated that in Russia there are some 230,000 yeguas dedicated to the production of kumis. Asna milk is one of the most similar to human composition. Successful studies have been conducted to provide food for allergic children to cow milk. There are also farms in Belgium that produce asna milk for cosmetic uses. One of the people of the so-called "longevas extremities", the Ecuadorian Maria Ester Capovilla, who died at the age of almost 117, claimed that the secret of her longevity was the daily consumption of this type of milk. Cebra milk has become an article demanded by eccentric millionaires.

Milking

A girl milking a cow manually

Machine that works by vacuum suction. Note that suckers reach the top of the nipple to prevent milk from coming out of the metal container while avoiding damage to the nipple.

There are basically two milking techniques:

• Manual: It is necessary to clean the animal's udder aseptically (i.e., with a special soap and always using drinking water) to avoid contagiarizing the animal with mastitis. Then, the milker's face should always see directly the cow's belly, position the right hand in a nipple of the udder, while with the left one grabs another, located on the same plane of the hand, but on the back plane of the udder, and then invest it constantly. This means that each hand will milk a pair of nipples; while one hand grabs the previous one of a pair, the other pulls the back of the other.

• Mechanics: Uses a sweater that milks the cow in the same order as the manual milking. He extracts the milk by making the vacuum. The difference is that it does it in less time and without risk of damaging the tissue of the udder. It is used in industries and in some farms with a high number of animals. Suctioners should be cleaned with a iodine solution at 4 %.

When milking, two tasks should always be performed:

1. Disinfect the nipple with distilled water: This is done with a mesh made of a sky blanket (a white fabric made with fine thread). When you shoot a chorrito of milk into it, you should see if the milk comes out unfilled, since this can mean that the cow has mastitis.

1. Selling the nipple: It is done with the same solution with which the suckers are cleaned. The difference is that the nipple is going to be completely cleaned with this solution to close the lactating duct. This prevents the nipple from getting infected. If the sweater caused a wound to the animal, because it has very sensitive skin, the iodine will prevent a subsequent infection.

Dairy Cattle Management Factors

Among other elements, the following must be considered:

• Regularity in care (ordeño, etc.).
• Avoid violence with animals.
• Avoid the presence of dogs or other causes of excitement and anxiety.
• Exercise. Cowboys spend nine hours a day. The percentage of the duration of the rest per day is 42-45 %, of the Romanian 25% and of the movements between 40-80 %.
• Cleaning animals. The breast should be especially clean; it is necessary to have clean beds.
• The cut of hooves is necessary in cows in stabulation.
• Eliminate or minimize vices. Mamon cows, who suck others and themselves. It is of unknown etiology and difficult solution; they are cows to dispose of unless they are of exceptional production. Cooking, usually due to bad treatment, milking or pain in milking (e.g., by the presence of cracks in the nipple).
• Temperament, which is conditioned by hereditary factors, physiopathological processes, the experience that the animal is acquiring and by learning.
• Social order, which is important in free stabulation, especially in medium and small groups. In large lots it affects a low percentage of cows. The creation of lots by age, level of production and ease for milking should be considered. At least two independent groups, one of cows in lactation and one of cows in drying have to be created.

• Examples of breast glands
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  Cow

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  Cerda

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  Oveja

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  Women

General characteristics

Not all milk from mammals have the same properties. As a general rule, it can be said that milk is a matt white and slightly viscous liquid, whose composition and physical-chemical characteristics vary significantly according to animal species, and even according to different breeds. These characteristics also vary in the course of the lactation period, as well as in the course of their treatment.

Milk provides humans with calcium, vitamins A and D, fatty acids and protein.

Physical properties

Cow's milk has an average density of 1.032 g/ml. It is a complex and heterogeneous mixture composed of a three-phase colloidal system:

• Solution: minerals as well as glucids are dissolved in water.
• Suspension: Protenic substances are found with suspended water.
• Emulsion: water fat is presented as emulsion.

It contains a significant proportion of water (about 87%). The rest constitutes the dry extract that represents 130 grams (g) per l and in which there are 35 to 45 g of fat.

Other main components are lactose carbohydrates, proteins and lipids. The organic components (carbohydrates, lipids, proteins, vitamins), and the mineral components (Ca, Na, K, Mg, Cl). Milk contains different groups of nutrients. Organic substances (carbohydrates, lipids, proteins) are present in more or less equal amounts and constitute the main source of energy. These nutrients are divided into building elements, proteins, and energy compounds, carbohydrates and lipids.

Chemical Properties

The pH of milk is slightly acidic (pH between 6.6 and 6.8). Another important chemical property is the acidity, or amount of lactic acid it contains, which is usually around 0.15-0.16%.

The protein substances of milk are the most important in the chemical aspect. They are classified into two groups: proteins (casein makes up 80% of the total protein, while whey proteins make up 20%), and enzymes.

Enzyme activity depends on two factors: temperature and pH; and it is present throughout the system in various ways. Phosphatase is an inhibitor at pasteurization temperatures and indicates good pasteurization. Reductase is produced by microorganisms foreign to milk and its presence indicates that it is contaminated. Xanthoxidase in combination with potassium nitrate (KNO₃) inhibits the growth of butyric bacteria. Lipase oxidizes fats and gives products a rancid odor and is inhibited by pasteurization. Catalase increases with mastitis and, although it does not deteriorate the food, it is used as a microbiological indicator.

Composition of milk

Immediately after giving birth, the female mammal begins to produce mammary secretions; during the first two or three days she produces colostrum. After this period, the animal properly synthesizes milk during the entire lactation period, which varies from 180 to 300 days (depending on many factors), with a highly fluctuating average daily production ranging from 3 to 25 liters. Milk is mainly synthesized in the mammary gland, but a large part of its constituents come from blood serum. Its chemical composition is very complex and complete, reflecting its great importance in feeding the young. The composition of the milk depends on the needs of the species during the rearing period.

Lactose

Lactose is a disaccharide present only in milk and its derivatives, representing the main and only carbohydrate. However, small amounts of glucose, galactose, sucrose, cerebrosides and amino sugars derived from hexosamine have been identified.

Lactose is synthesized in the mammary gland by an enzymatic system in which α-lactalbumin intervenes and is later secreted into milk. It is 15% less sweetener than sucrose and contributes, along with salts, to the overall flavor of the food. The lactase enzyme hydrolyzes the glycosidic bond and separates the sugar into glucose and galactose, but its level varies among different human populations. In humans, several genetic mutations have allowed lactose tolerance to continue into adulthood (lactose persistence), with greater or lesser prevalence depending on the geographical area. Populations that do not have this mutation (which are mainly Asian and African) have a primary or permanent lactase deficiency.

Healthy people with primary or permanent lactase deficiency are able to consume at least 12 g of lactose per meal (the amount found in one cup of milk) without experiencing any or only mild symptoms. This tolerance improves if milk is consumed with meals, choosing low-lactose milk, replacing milk with yogurt or cured cheeses, or taking lactase supplements. Likewise, regular consumption of dairy foods by people with primary deficiency of lactase may allow a favorable adaptation of colonic bacteria, which may assist in the breakdown of lactose, allowing progressive and sustained lactose tolerance.

When the body is not able to properly assimilate lactose and consumption exceeds the tolerated limit, various symptoms of intolerance (lactose intolerance) may appear, such as abdominal pain, bloating, rumbling, diarrhea and even constipation and vomiting. However, the consumption of dairy products by people with lactose intolerance does not cause damage to the gastrointestinal tract, but is limited to these transient symptoms. A large proportion of people who believe they have lactose intolerance lactose intolerance do not actually have lactose malabsorption, but their symptoms are due to the presence of undiagnosed diseases, such as celiac disease, inflammatory bowel disease, or bacterial overgrowth. Also, lactose intolerance is often confused with a milk allergy, especially difficult to diagnose when non-IgE mediated.

Lipids or fats

The properties of milk are a reflection of the fatty acids it contains. Thus we have several groups of lipids present in milk: triacylglycerides, diacylglycerides, monoacylglycerides, phospholipids, free fatty acids, sterols and their esters, and some carbohydrates.

Triaglycerides are found as small particles called globules. They contain a large amount of fatty acids, identifying up to 400 different types in cow's milk (oils have between 8 and 10). Milk is the food with the most complex lipid composition. However, 96% of the total is made up of only 14 fatty acids, the most important being myristic acid, palmitic acid and oleic acid. The large amount of fat is due to the bovine diet and the intense activity of the rumen. In the case of seals, the excess fat content is due to the fish-based diet and is part of a natural adaptation for the Breed withstand extreme cold. In the case of human milk, the fat content depends on the balanced nutrition of the woman during pregnancy and lactation; hence a fully omnivorous diet benefits the exact fat content of the milk.

Caseins

Of all the proteins present in milk, the most common and representative are three, and they are all caseins: α_s1-casein, β-casein and κ-casein. In the dairy industry, κ-casein is very important, which has, among others, the following characteristics:

Kap-casein is useful mainly for making cheeses (the richest in this type of casein is cow's milk, while the poorest comes from human milk) because when it is hydrolyzed by Renin may be precipitated into paracasein-κ, which reacts with calcium to generate calcium paracaseinate.

The micellar phase

Caseins interact with each other to form a colloidal dispersion consisting of spherical particles called micelles with a diameter that usually varies between 60 and 450 nm, with an average of 130 nm. Despite the abundant scientific literature on the possible structure of a micelle, there is no consensus on the subject. There is a proposed model that considers that the micelle is in turn made up of subunits of the same shape, with a diameter of between 10 and 20 nm.

The model illustrated above allows us to observe how the subunits are linked together thanks to calcium ions. It is suggested that calcium phosphate binds to the NH₂^- groups of lysine; calcium interacts with the ionized carboxyl group (COO^-). Submicelles are formed from the constant interaction between α, β and κ caseins. The stabilizing function of κ-casein against calcium precipitation from other protein fractions must be highlighted. The large number of physicochemical models (to name a few: Rose, Garnier and Ribadeau, Morr, Schmidt, Slattery, Waugh, Noble, etc.), all agree that the hydrophobic units between protein molecules ensure the stability of the micelle.

Buttermilk

From 10 liters of cow's milk you can produce 1 to 2 kg of cheese (i.e. mostly casein) and an average of 8 to 9 kg of whey. Whey is the set of all the components of milk that are not integrated into the coagulation of casein, and according to the type of milk (that is, the species from which it comes) you can have two types of whey, classified by their taste:

• The sweet serum, which comes from coagulated cheeses with renin. Most of this serum is composed of non-protein nitrogen (22 % of the total) and has a large concentration of lactose (about 4.9 % of all serum); it is the richest of proteins (0.8 %) but very poor in the issue of lactic acid (0.15 %). The rest of the serum is a set of salts, minerals and fats that vary from species to species. The pH ranges between 6 and 6.2.
• The acid serum, which comes from coagulated cheeses with acetic acid. It is the common by-product of the manufacture of white cheese and cheese and low pH (4.6) is corrosive for metals. It contains a higher proportion of non-protein nitrogen (27 % of the total) and has less lactose in concentration (4.3 %) since, due to acid milk, part of the lactose becomes lactic acid by fermentation. Therefore, it has more quantity of lactic acid (0.75 %). Because of denaturalization, it is poorer in proteins (0.6 %). It usually has less concentration of salts, minerals and fats, whose concentrations vary from species to species.

Lactates and phosphates (very common salts in whey) help to maintain the acid-base balance and greatly influence the properties of whey (stability and thermal precipitation). Whey has a low proportion of proteins, however they have more nutritional quality than cheese caseins. The excessive production of whey when making cheese has always been a concern and many ways have been devised to take advantage of it. One of the simplest, homemade, is to heat it to precipitate the proteins and then press or filter it. In many towns in Mexico it is usually eaten immediately after being salted (and is called cottage cheese). Its industrial applications usually come once it is dehydrated, when it is poorly soluble. During evaporation (to remove water) and spraying (to dry it) it can lose its nutritional properties, so the pH and temperature of these two processes must be carefully monitored during extract drying.

Whey proteins are compact, globular, with a molecular weight ranging from 14,000 to 1,000,000 daltons, and are soluble over a wide pH range (they remain intact when milk is naturally cut, since that there has been no presence of heat that denatures the proteins). In their natural state they do not associate with caseins, but in heat-treated and homogenized milk, a part of these proteins do. Whey proteins consist of at least 8 different fractions, all sensitive to high temperatures (thermal processes).) and for this reason they are the first to degrade with processes such as pasteurization or UHT. The reason why milk does not decompose outside of refrigeration once heat-treated is because whey proteins, when denatured, release a sulfhydryl group that partially reduces oxidation activity. The most important whey proteins in milk are:

(a) α-lactalbumin: constitutes the enzymatic system required for lactose synthesis. Animal milks that do not present this protein also does not contain lactose. It does not have free sulfhydrates but it does four disulfuros that give up the cystines, so it has 2.5 times more sulfur than casein. It has low molecular weight and a high content in tryptophan. It is considered that a long time ago, birds and bovines were joined by a common genetic trunk (not taxonomic) because the amino acid sequence of this protein is similar to the lipsosome of the egg. It denaturalizes at 63 °C.

(b) β-lactoglobulin: insoluble in distilled water and soluble in salt dilutions, it denaturalizes and precipitates less than 73 °C (does not resist pasteurization). This protein is not found in human milk, being abundant especially in ruminants and is considered responsible for certain allergic reactions in infants. There are industrial treatments that make it possible to modify the components of cow's milk to look like those of human milk and thus be able to give it to babies. In these processes this protein fraction is eliminated by precipitation with polyphosphates or by gel filtration, to then mix it with other components (caseine, soy oil, minerals, vitamins, lisozima, etc.).

(c) Serum acid protein (WAP): is a milk component that is only in the category GLIRES, which groupes rodents and lakemorphs, although related sequences have been found in the pig. From the fact that they contain domains similar to protease inhibitors it is observed that their function is antimicrobial and protective of oral mucosa.

(d) immunoglobulins: they add 10% of the total serum proteins and come from the animal's blood. They belong to IgA and IgE types and come from the plasma cells of the joint breast tissue (Bloom-Fawcett, 1999). Some scientists, as mentioned above, see in it the reason for being milk, as they allow to transmit some immunity to the child (mainly the memory of the diseases that the mother has suffered). They are usually very abundant in the caloster (up to 100 g/L).

Microbiological properties

Newly obtained milk is an ideal substrate for a large number of bacterial genera, some beneficial and others harmful, which cause various alterations to the food and its properties:

As a quality control, raw milk or raw milk (unpasteurized) is analyzed before determining the destination as a finished product, if the germ count is greater than 100,000 UFC (Colony Forming Units) it is a milk of lower quality than one whose count is less than that number. The potential for brucellosis that could present is also determined.

Nutritional properties

Its diversified composition, which includes fats (where triglycerides are the majority fraction with 98% of the total lipid and whose fatty acids that form them are mostly saturated), proteins (casein, albumin and whey proteins) and carbohydrates (lactose, specific milk sugar), make it a complete food. In addition, whole cow's milk is an important source of vitamins (vitamins A, B, D3, E). Vitamin D is what binds calcium phosphate to teeth and bones, which is why it is especially recommended for children. Colostrum is a yellowish liquid, rich in proteins and antibodies, essential for the immunization of the newborn. Despite this, it has no industrial application.

Industrial processes

Raw milk or raw milk would not be suitable for sale and consumption without being subjected to certain industrial processes that ensure that the microbiological load is within safe limits. For this reason, milk with health guarantees must have been milked with modern and hygienic suction methods in which there is no physical contact with the milk. After milking, it has to be cooled and stored in an agitated milk tank and transported in isothermal tankers to the processing plants.

In these plants, the milk must be analyzed before unloading to see that it meets optimal characteristics for consumption.

Among the analyses, there are the physicochemical ones to see its composition in fat and dry extract, among other parameters, to detect possible fraud due to watering down, the organoleptic ones, to detect strange flavors and the bacteriological ones, which detect the presence of pathogenic bacteria and of antibiotics. These pass into the milk from the cow undergoing veterinary treatment and in turn pass to the consumer. Milk that does not meet the quality requirements must be rejected.

Once its optimal state has been verified, it is stored in large-capacity tanks and ready for commercial packaging.

Debugging

Depending on its commercial application, milk can go through a large number of processes, known as purification processes. These ensure the sanitary quality of the milk, and are listed below:

• Filtration is used to separate the protein from the serum and thus remove impurities such as blood, hair, straw, manure. A filter or a grid is used.
• Homogenization: This physical process is used which consists of continuous agitation (neumatic or mechanical) either with a pump, a homogenizer or a clarifier, and whose purpose is to decrease the fat blood cell before heating it and thus prevent nata being formed. This should be 1 μm (micrometer) in diameter. When milk is standardized or fat content is regulated, it mixes with homogenization, avoiding the subsequent separation of phases. It is done at 50 °C to avoid denaturalization. Homogenization, after pasteurization, stabilizes fat in small particles that prevent cremation during fermentation and generates a better texture since the interaction between caseins and fat cells becomes favorable to make dairy derivatives that require fermentation.
• Standardization: When a milk does not pass positively the fat content test to produce a particular product, milk is used in powder or vegetable fat. It is done in two ways: first mathematically (with procedures such as Pearson's χ2 or Material Balance) and the other practice, measuring the masses and mixing them. Before milk passes to any process, it must have 3.5 % of fat content. This process is also used when the milk, once treated thermally, lost some type of components, which is more commonly done with the milk that loses calcium and to which new nutrients are reinstated.
• Deodorization: it is used to remove the odors that could impregnate the milk during its harvest (e.g. manure). For this, a vacuum chamber is used, where the smells are completely eliminated. Milk must smell sweet or acidic.
• Bactofugation: removes bacteria by centrifugation. The machine designed for this function is called bactófuga. It generates a centrifugal rotation that causes bacteria to die and separate from milk. Milk must have 300 000 UFC/mL (Colonial forming units per milliliter). Before a bactofugation is performed a culture of the bacteria in the milk and identify them, this is very important as it allows to determine the most effective procedure to remove a specific bacteria. It is usually taken as a standard that 1800 seconds warming at 80 °C eliminates the coliforms, the bacillus of tuberculosis and spores; as well as the inhibition of phosphatase alkaline and peroxidase enzymes. But this is just a very variable standard that depends on many conditions.
• Clarification: is used to separate unnecessary solids and sediments present in milk (such as dust or soil, very small particles that cannot be filtered). A clarifier is used, where the process can be performed in two ways: heating the milk at 95 °C and letting it stir for 15 minutes, or heating it at 120 °C for 5 minutes.

Thermal treatments

Once purification is complete, milk can be treated for human consumption by applying heat to partially or totally eliminate bacteria.

According to the required objective, thermization, pasteurization, ultra-pasteurization or sterilization will be used.

• Term: with this procedure the enzyme activity is reduced or inhibited.
• Pasteurizationslow high temperatureSHT): with this procedure milk is heated at temperatures determined for the elimination of specific pathogenic microorganisms: mainly known as Streptococcus thermophilus. It inhibits some other bacteria.
• Ultrapasteurization (ultra high temperature, UHT): in this procedure is used higher temperature than in pasteurization. Removes all bacteria except lactics. No further cooling required.
• Sterilization: the high temperature used of 140 °C for 45 s eliminates any microorganism present in the milk. It is not refrigerated later; this milk is also called hygienized. This process does not apply to flavored or reformulated milks as they would be swollen.

Sterilization can occur in online autoclaves called Barriquands. The white milks treated in this way are packed in tetra brik or special sanitized cardboard boxes and internally covered with a satin film.

After a heat treatment, refrigeration may be dispensable because it is not necessary to lower the temperature in all cases, only when the milk still has microorganisms.

According to the outgoing microbial quality, refrigeration is considered; hence the thermization has forced refrigeration and the sterilized one does not. If there are no bacteria or enzymatic activity, the milk will not spoil at room temperature; if we leave any milk in a glass and uncovered then the oxygen will do the same as an oxidizing agent, but not due to internal activities of the milk.

Presentation of milk in the market

The variety of dairy products available on the market and the different milk treatments is increasing, as the top picture of a Swedish market is explicit.

The presentation of milk in the market is variable, since it is accepted as a general rule the alteration of its properties to satisfy the preferences of the consumers. A very frequent alteration is to dehydrate it (lyophilization) as powdered milk to facilitate transport and storage after milking. It is also common to reduce the fat content, increase the calcium content, and add flavors.

The requirements that a product must meet to be placed in the different categories vary greatly according to the definition of each country:

• Enter has a fat content of 3.1 % (e.g. in Chile) and 3.8 % (e.g. in Switzerland).
• Milk without lactose is subjected to an enzymatic hydrolysis process in which lactose is transformed into glucose and galactose to make it more digestible for people who are lactase-deficient.
• Uncreated or unborn milk fat content below 0.3 %.
• Semidescremada o semidesnatada with a fat content between 1.5 and 1.8 %.
• Flavored is the sugary or sweetened milk to which flavors such as strawberry, cocoa powder (bebida known as chocolatada), cinnamon, vanilla, among others. They are usually unborn or semi-unborn.
• Galatita: hard plastic obtained from the cuajo of milk or more specifically from casein and formol.
• Powder or Liofilized: This milk has been extracted 95% of water through atomization processes, and evaporation. It is presented in a creamy powder. For your consumption you only have to rehydrate it with water or milk.
• Condensed, concentrated or evaporated: This milk has been partially extracted from water and is much thicker than normal fluid milk. It may contain added sugar.
• Enriched dairy preparations are added to those products of nutritional value such as vitamins, calcium, phosphorus, omega-3, etc.

Health effects of milk consumption

Beneficial

• A 1993 study states that a proper intake of milk in childhood and adolescence through milk and dairy products is a decisive marker for obtaining the maximum bone mass and thus preventing osteoporosis.
• Instead, intake of milk in postmenopausal women does not seem to reduce the risk of osteoporosis, as do vitamin D supplements.
• A study of more than 136 000 people between 35 and 70 years, developed for 15 years on the 5 continents, published in 2018, associated the taking of 3 or more daily rations of milk or dairy, especially integers (not denated or semi-denated) with a lower mortality (3.4 %) cardiovascular than those who did not take dairy (5.6 %).
• An article by the Organization of Consumers and Users states that those who habitually take milk weigh between 1 and 3 kilograms less than those who do not ingest it. This is apparently due to the fact that the calcium of milk limits the absorption of fat in the digestive system.
• Harvard School of Public Health states that milk intake reduces the risk of osteoporosis and colon cancer.

Harmful

Simplified representation of a lactose molecule breaking into glucose (2) and galactose (1).

• People with lactose intolerance, who do not produce enough lactase enzymes due to genetic causes (primary lactose intolerance) or diseases that damage the small intestine (intolerance to secondary lactose or acquired), may have digestive discomfort if they ingest milk in high amounts, although in most cases they may take cheese or yogurts without problems. Anyone with primary (genetic) intolerance whose intestine is healthy is able to consume at least 12 g of lactose in each meal (the amount contained in a cup of milk) without experiencing any symptoms or only mild symptoms. Reactions to smaller amounts of dairy indicate the existence of an undiagnosed bowel disease (mainly celiac disease and non-kali gluten sensitivity) or allergy to milk proteins.
• A small percentage of the population (less than 1 percent) suffers from allergy to the AMR cow's milk protein (IPLV). People allergic to this protein should not take dairy.
• Harvard School of Public Health states that the intake of a lot of dairy (more than two glasses of milk a day) doubles the risk of prostate cancer and probably increases (in any case modestly) the risk of ovarian cancer.
• Harvard research concluded that twelve of fourteen case-control design studies and seven of nine cohort studies demonstrated a positive association between a certain number of dairy products and prostate cancer. In these studies, men who consumed more dairy products had about twice the risk of contracting prostate cancer and a four-fold greater risk of metastasis or prostate cancer with fatal consequences, compared to those who consumed little of those foods.

Denomination «milk» for products of plant origin

The so-called vegetable milks have become popular as alternatives to milk of animal origin that can be made from various raw materials, such as rice, coconut, barley, almonds, oats, soybeans, hazelnuts, millet or peanuts. They are usually consumed by vegans, who refrain from eating all products of animal origin. However in most countries it is not legal to call "milk" to products of plant origin; They are often referred to as "juices" or "drinks", and the term "milk" is considered only applicable to fluids from mammalian glands.

Consumers misunderstand that "milks" Vegetable milk is a direct substitute for cow's milk, but most of these beverages lack the nutritional balance of animal milk, are low in protein, fat, calories, and iron, and some are extremely low in protein and calcium. They are not an adequate substitute for breast milk, infant formulas or cow's milk in the first two years of life. In the case of children over two years of age who cannot consume milk for medical reasons, the recommendation is to choose fortified drinks that contain at least 6 g. of protein per 250 ml.

In the European Union and Latin America

In order not to confuse the consumer, in the countries of the European Union since 2013 the legislation prohibits the use of the word "milk" to designate vegetable drinks.

It will be understood by "milk" exclusively the normal breast secretion obtained from one or more ordenos, without any addition or extraction.

Regulation (EU) No. 1308/2013 of the European Parliament and the Council of 17 December 2013. L 347/814

The Official Mexican Standard NOM-155-SCFI-2012 considers «milk» only the «product obtained from the secretion of the mammary glands of cows» (it literally and legally dismisses the mammary secretions of the rest of other mammalian species).

The Ministry of Agriculture of Peru also does not include any product of plant origin in the definition of milk.

Current Perspective

For some time it was speculated that rickets could be caused by a deficiency in the diet, which could be related to low milk consumption. But it was observed that children in urban areas and temperate climates frequently developed rickets, so it began to be suspected that lack of sun exposure could be the triggering factor. Finally, in 1919 it was observed by Mellamby et al. that both the administration of cod liver oil as the main source of vitamin D and exposure to the sun cured rickets. This proposition was made in 1912 by Casimir Funk, upon discovering and coin the term vitamin. Nowadays, the consumption of milk has led certain companies to create a variety of products that have similar characteristics to those of milk, advertising that its consumption helps prevent arthritis, osteoporosis and other conditions related to bone demineralization; at the same time that certain nutritionists recommended its daily consumption in the 1980s.

Subsequent studies indicate that it is not so much the amount of calcium that we ingest that matters, but the amount that we lose daily in the urine, due to our lifestyle. The higher the intake of protein, especially of animal origin (including milk and cheese), the greater the amount of calcium that is lost in the urine.

As for heartburn (commonly known as “heartburn”), a burning sensation in the esophagus caused by the regurgitation of gastric acid, milk was long believed to be an effective treatment to eliminate it. Although it can counteract this symptom because it is a slightly acidic substance (close to neutrality 6.5 to 6.8), at the same time calcium and casein stimulate the secretion of gastric juices causing a "rebound" that can increase the acid.

Production and distribution

Glass bottles used in the English dairy delivery system.

The 20 largest producers of cow milk in 2018 (tonnes, or thousands of liters)
United States	98.690.477
India	89.833.590
BrazilBrazil	33.839.864
GermanyGermany	33.064.833
ChinaChina	30,745,600
Russia	30.345.525
France	25.541.269
New ZealandNew Zealand	21.392,000
TurkeyTurkey	20.036.877
PakistanPakistan	16.722,000
United KingdomUnited Kingdom	15.311,000
PolandPoland	14.171.153
Mexico Mexico	12.005.692
ItalyItaly	11.944.450
NetherlandsNetherlands	10.634.163
Argentina	10.526.600
UzbekistanUzbekistan	10.415.660
Ukraine Ukraine	10.064,000
Australia	9.289,000
Ireland	7.810.260
Amount of the twenty countries	512.384.013

The production of milk begins from the artificial insemination of cows to get them pregnant and so that they begin to produce the necessary hormones so that their mammary glands begin to generate it, naturally, to later breastfeed their calf. Once this effect is generated, the calf is totally or partially removed from its parent specimen to give rise to the extraction of milk for human consumption.

Because it has a short expiration period (especially if it is kept fresh) it should be distributed as soon as possible after milking. In several countries milk is usually delivered to households on a daily basis, but economic pressures have made this service less and less popular. In some areas, moreover, the dispersion makes it practically impossible to distribute milk. In these cases, people choose to buy milk in establishments such as supermarkets, dairy stores, self-service stores or neighborhood stores. Before the popularization of plastic containers or tetra briks, (which were initially created especially to better preserve the properties of dairy products) milk was sold in paper wrappers and glass bottles.

In some countries, such as the United Kingdom, it is customary for a milkman to deliver milk to the neighborhood in the morning. The milk is delivered in glass bottles with aluminum caps in front of the house. Silver-colored caps mean that the milk is homogenized, silver-red indicates semi-skim, silver-blue indicates that the milk is skim, and gold indicates that it comes from the island channel.

Empty bottles are recycled. The milkman returns the next day to leave a new filled box and take the empty bottles to be refilled and delivered again the next day. Currently some franchises are opposed to the daily distribution and opt for longer intervals. This form of distribution is also common in the US.

Today, the improvement of the packages and containers that contain milk has allowed its consumption with low conservation requirements to be possible in almost the entire world.

Culinary applications

The flavor provided by milk is slightly sweet (due to lactose), prolonged cooking of milk causes the Maillard reaction between lactose and milk proteins, giving rise to toasted colors. Many of the properties of milk disappear when mixed in dishes, one of its fundamental uses is to provide moisture to some preparations, timidly contributing to flavors and textures. It is important to mention that a large part of dairy products are used in some cuisines around the world, in some of them such as Turkish cuisine, India or Mexican cuisine, they are known for their variety and offer of diverse recipes.

Milk is an ingredient in some soups (mainly cream-type), where it is added to enhance certain flavors. It is also sometimes used when scrambling eggs so that they take longer to set, in mashed potatoes, in the preparation of sauces such as bechamel and in desserts such as rice pudding, flans (puddings), the typical tres leches cake, semolina with milk (Chili), ice cream, etc. It is widely used in drinks such as coffee with milk (expressed in latte art), milkshakes, hot chocolate, meringadas, chicha (Venezuela), etc. It is even part of some alcoholic beverages such as the Venezuelan Ponche Crema, eggnog, etc.; in some cocktails or simply taken mixed with drinks such as aniseed.

Milk and its cultural connotation

Milk is one of the most important livestock products. Table Milk, of Vermeer, could enclose, according to some interpretations, symbolic elements, such as the softness of milk to the nobility of this maid in her work, which would have raised criticism in her time.

Image of the plant chicken milk (Ornithogalum umbellatum).

Milk has not only been valued as food by humans, but is the basis of symbolic interpretations. An example of this is the name of the Milky Way (galaxy in which our solar system is located). The great belts of stars that can be seen between the constellations of Perseus, Cassiopeia and Cepheus, were baptized as the Milky Way to remember the story in which Hera wanted to breastfeed Heracles (Hercules, in Roman mythology), and he bit her so strong that a jet of milk shot out into the cosmos.

Milk and its derivatives have given rise to myths from India to Scandinavia. In the Old Testament they appear as symbols of abundance and creation. It was taken as an offering to the gods and therefore it was considered a divine act related to life.

Milk can also symbolize beauty and feminine aesthetics. Cleopatra used milk baths to enhance her beauty and take advantage of the properties that milk offers to the skin.

Because of its always constant color (with shades of yellowish white in all species) it has received religious connotations, such as purity. In the work The Milkmaid by the Dutch painter Vermeer, the whiteness of the milk alludes to the purity and virtues of the young woman. Some of the most famous cheeses are associated with the main producing country. Thus, Roquefort cheese is typical of France, mozzarella and gorgonzola blue cheese in Italian dishes, or Zamorano from the region of Castilla y León, in Spain.

In botany, the white of milk was compared to the color of chickens to name the plant Ornithogalum umbellatum as Hen's milk, a plant native to the Mediterranean from the family Liliaceae.