1 milk hygiene.pdf

8/11/2019 1 Milk Hygiene.pdf

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ILK YGIENE

1yDr. Sameh Abuseir

07.09.2011


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MILK IS A PERFECT FOOD

Milk is defined as the secretion of the mammaryglands of mammals, its primary natural function

being nutrition of the young.

Milk of some animals, especially cows, buffaloes,,

consumption, either as such or in the form of a.

o an ma s s es gne y e an ma o yonly for the offspring of like kind during the firstew mon s o grow .


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The milk of domestic ruminants is diverted by

man for his own use.

Fermented products such as cheeses werediscovered accident ut their histor has also

been documented for many centuries, as has theroduction of concentrated milks utter and even

ice cream.

In addition to being the best single substitute for ,

foods through infancy, adolescence, and even in.


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The role of milk in the traditional diet has varied greatlyin different re ions of the world.

The tro ical countries have not been traditional milk consumers, whereas the more northern regions of the

world, Europe (especially Scandinavia) and Northmer ca, ave tra t ona y consume ar more m

and milk products in their diet.

In tropical countries where high temperatures and lack

store fresh milk, milk has traditionally been preserved

through means other than refrigeration, includingimmediate consumption of warm milk after milking, by

boiling milk, or by conversion into more stable products.


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Table 1. Per Capita Consumption of Milk and Milk Products in Various Countries, 2005 data.

Country Fluid Milk (Litres) Cheeses (kg) Butter (kg)

n an . .

. Norway 100.8 14.8 1.7 New Zealand 94.3 4.8 3.9

we en . . .Spain 92.7 6.9 0.2

Australia 80.8 7.1 0.8. . .

United States 67.8 5.5 0.7 Netherlands 60.3 10.7 1.4

. . .European Union (25 countries) 57.2 5.8 1.0Germany 54.5 9.4 3.3

. . .

Switzerland 51.3 11.6 2.4 Mexico 51.3 5.0 N/A

. . .France 46.4 13.6 2.9 Argentina 33.5 5.4 0.8

. . .

Ireland 19.1 3.5 2.3 China 2.5 N/A N/A


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a e . ow m pro uc on onnes n se ec e coun r es n e wor .

United States 77,470India 38,500Germany 28,180France 23 970Brazil 23,300China 18,850

ew ea an ,United Kingdom 14,400Poland 12,700

Netherlands 10,630Italy 10,400

,Mexico 9900Canada 7540


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M ILK B IOSYNTHESIS

Milk is synthesized in the mammary gland.

Within the mammary gland is the milk producing, .epithelial secretory cells surrounding a central

,a duct system . The secretory cells are, in turn,surrounded b a la er of m oe ithelial cells andblood capillaries .

Milk components are for the most part formed in the

are the results of digestion.


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Mammals digest their food by the use of enzymes to- -, , ,

especially monosaccharides; small peptides andamino acids; and fatty acids and monoglycerides.

These are taken up in the blood, together with other , , ,acids, etc.

The substances are transported to all the organs in the body, including the mammary gland, to provide

metabolism, including the synthesis of proteins,

lipids, etc.

In ruminants like the cow, considerable predigestion,

occurs for the most part in the first stomach or rumen.


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The rumen may be considered as a large and very

complex io-fermenter. It contains numerous bacteria that can digest cellulose, thereby

reaking down plant cell walls, providing energy

and liberating the cell contents.

From cellulose and other carboh drates aceticpropionic, butyric and lactic acid are formed,which are taken u in the lood.

depends on the composition of the feed. Proteins.


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The rumen flora uses these to make proteins butcan also synthesize amino acids from low-molar-

mass nitrogenous components.

Further on, in the digestive tract the microbes are

digested, liberating amino acids. Also, food lipidsare y ro yze n t e rumen an part ymetabolized by the microorganisms. All these

.

e syn es s o m componen s occurs or egreater part in the secretory cells of the mammary

.components are taken up from the blood, and at

the lumen.


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Proteins are formed in the endoplasmic

reticulum and transported to the Golgi vesicles ,in which most of the soluble milk components arecollected.

The vesicles grow in size while being transportedthrou h the cell and then o en u to release their contents in the lumen.

Triglycerides are synthesized in the cytoplasm ,,

are transported to the apical end of the cell.


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They become enrobed by the outer cell membrane

(or plasmalemma) while eing pinched off intothe lumen. This type of secretion is calledmerocrine , which means that the cell remains

intact.

The raw materials for milk roduction aretransported via the blood stream to the secretorycells. It takes 400-800 L of lood to deliver components for 1 L of milk.


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ExcretionThe glandular epithelium, consisting of layers of secretory cells, form spherical bodies called alveoli .Each of these has a central lumen into which the

freshly formed milk is secreted. From there, the milk can flow through small ducts into larger and stilllarger ones until it reaches a cavity called the cistern.

From the cistern, the milk can be released via the teat.A cow has four teats and hence four separate

mammary glands, commonly called (udder) quarters.

Excretion of the milk does not happen spontaneously:

the alveoli have to contract, which can be achieved bythe contraction of muscle tissue around the alveoli.


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Contraction is induced by the hormone oxytocin .

This is released into the lood y stimulation of the teats of the animal, be it by the sucklingyoung or y the milker. The udder is not fully

emptied.


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LactationWhen a calf is orn, lactation, i.e. the formationand secretion of milk, starts.

The first secretion greatly differs in compositionfrom milk.

Within a few days the milk has become normaland milk yield increases for some months, after which it declines.

The yield greatly varies among cows and with theamount and the quality of the feed taken by thecow.


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For milk cows, milking is generally stopped after

about 10 months, when yield has ecome quitelow. The duration from parturition to leaving thecow dry is called the lactation period, and the

time elapsed after parturition is the stage of lactation.


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Colostrum

Colostrum is a form of milk produced by themammary glands of mammals in late pregnancy.Most species will generate colostrum just prior to

giving birth.

newborn against disease, as well as being lower in.

o os rum s cruc a or new orn arm an ma s.They receive no passive transfer of immunity via

e p acen a e ore r , so any an o es athey need have to be ingested.


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This oral transfer of immunity can occur because

the newborn's stomach is porous. This means thatlarge proteins (such as antibodies) can passthrough the stomach wall.

The newborn animal must receive colostrumwithin 6 hours of ein orn for maximal transfer

of antibodies to occur.

The stomach wall remains somewhat open up to, .

Livestock reeders commonly ank colostrumfrom their animals.


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Colostrum produced on a breeder's own premises is

considered to e superior to colostrum from other sources, because it is produced by animals alreadyexposed to (and thus, making antibodies to)

pathogens occurring on the premises.

A German stud re orted that multi arous mares

produced on average a liter (quart) of colostrumcontainin 70 rams of I G.

permitted to nurse; rather, they are fed colostrum

a bottle then a bucket.


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HumanHuman consumptionconsumption of of bovinebovine colostrumcolostrum

Assertions that colostrum consumption is of human benefit are questionable because mostingredients undergo digestion in the adult

stomach, including antibodies and all other proteins.

Bovine colostrum and its components are safe for ,

intolerance or allergy to lactose or other .

s ows prom se n e rea men or preven onof a variety of disease states.


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Bovine colostrum from pasture-fed cows contains

immunoglobulins specific to many human pathogens,including Escherichia coli , Cryptosporidium parvum ,Shigella flexneri , Salmonella, Staphylococcus ,[27]

and rotavirus (which causes diarrhea in infants).

Before the develo ment of antibiotics colostrum was

the main source of immunoglobulins used to fightinfections.

,against polio, the immunoglobulin he used came

.


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When antibiotics began to appear, interest in

colostrum waned, ut, now that antibiotic-resistant strains of pathogens have developed,interest is once again returning to natural

alternatives to antibiotics, namely, colostrum.


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S OME PROPERTIES OF MILK :

as a o u on: s a u e aqueous so u on an e aves

accordingly.

Because the dielectric constant is almost as high as thatof pure water, polar substances dissolve well in milk

an sa ts ten to ssoc ate (a t oug t s ssoc at onis not complete).

The ionic strength of the solution is about 0.073 M. The

pH of milk is about 6.7 at room temperature.

The viscosity is low, about twice that of water, whichmeans a m can rea y e m xe , even yconvection currents resulting from small temperaturefluctuations.


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The dissolved substances give milk an osmotic

pressure of about 700 kPa (7 bar) and afreezing-point depression.

The water activit is hi h about 0.995.

20C; it varies especially with fat content


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Milk as a Dispersion:

Milk is also a dispersion; the particles involvedare summarized. This has several consequences,suc as m e ng w te.

The fat globules have a membrane, which acts asa kind of barrier between the plasma and the core p s. e mem rane a so pro ec s e g o u es

against coalescence. The various particles can be.

e a g o u es can e concen ra e n a s mp eway by creaming, which either occurs due to

centrifugation.


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In this way cream and skim milk are obtained.

Skim milk is not identical to milk plasma, thoughquite similar, because it still contains some smallfat globules.

Cream can be churned, leading to butter andbuttermilk the latter is rather similar in

composition to skim milk.

Likewise, casein micelles can be concentrated and, ,

filtration. The solution passing through the.


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If the pores in the membrane are very small, also

the serum proteins are retained.

When adding rennet enzyme to milk, as is donein cheese makin the casein micelles start toaggregate, forming a gel; when cutting the gelinto ieces these contract ex ellin whe .

, because it contains some of the fat globules and

- .

Casein also aggregates and forms a gel when the pH of the milk is lowered to about 4.6.


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Water can be removed from milk by evaporation.

Altogether, a range of liquid milk products of various compositions can be made.


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Flavor:The flavor of fresh milk is fairly bland.

The lactose produces some sweetness and the.

several small molecules present in very smallquantities also contribute to flavor.

The fat lobules are res onsible for thecreaminess of whole milk.


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Nutritional value:

Milk is a complete food for the young calf, and itcan also rovide ood nutrition to humans.

,significant quantities.

It is poor in iron and the vitamin C content is nothigh. It contains no anti-nutritional factors, but itlacks dietary fiber.


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Milk as a Substrate for Bacteria:

Because it is rich in nutrients, manymicroor anisms es eciall acteria can row inmilk.

Not all bacteria that need sugar can grow in milk,.


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Milk is poor in iron , which is an essential nutrient

for several acteria, and contains someantibacterial factors, such as immunoglobulinsand some enzyme systems.

Milk contains too much oxygen for strictlyanaerobic acteria. Alto ether the rowth of

several bacteria is more or less restricted in rawmilk but several others can roliferate es eciallat high ambient temperatures.

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