1. Milk

2. Where does milk come from?
For young mammals and human infants, milk is the first food ingested. It continues to be the sole constituent of the diet for a considerable period of time
Milk is a complex biological fluid, the composition and physical characteristics of which vary from species to species
The major constituent of milk is water, but depending on the species, milk contains varying quantities of lipids, proteins and carbohydrates that are synthesized within the mammary gland

3. Species
Water
Fat
Casein
Whey protein
Lactose
Ash
Human
87.1
4.6
0.4
0.7
6.8
0.2
Cow
87.3
4.4
2.8
0.6
Buffalo
82.2
7.8
3.2
4.9
0.8
Goat
86.7
4.5
2.6
Sheep
82.0
7.6
3.9
4.8
0.9
Horse
88.8
1.6
1.3
1.2
6.2
Rat
79.0
10.3
6.4
2.0
Ass
88.3
1.5
1.0
7.4
0.5
Reindeer
66.7
18.0
8.6
Camel
86.5
4.0
2.7
5.4

6. Minerals and vitamins in milk
Milk contains a number of minerals, with a total concentration of < 1%
The most important salts are calcium, sodium, potassium and magnesium.
 Milk contains many vitamins and among the best known are A, B1, B2, C and D. Vitamins A and D are soluble in fat, or fat solvents, while the others are soluble in water.

7. Enzymes in milk
LIPASE splits fat into glycerol and free fatty acids, excess free acids in milk and milk products result in a rancid taste
PEROXIDASE is inactivated if the milk is heated to 80 °C for a few seconds, its detection is used to check on pasteurization

8. Enzymes in milk..cont
CATALASE splits hydrogen peroxide into water and free oxygen. Milk from diseased udders has a high catalase content
PHOSPHATASE is able to split certain phosphoric-acid esters into phosphoric acid and alcohol. Phosphatase is destroyed by ordinary pasteurisation

9. The mammary gland

10. Mechanism of milk formation
Estrogen and progesterone are essential hormones for physical development of breast during pregnancy
These hormones inhibit the actual secretion of milk
Prolactin is secreted by a mother pituitary gland, and its concentration in her blood raises steadily from the 5th week of pregnancy until birth of the baby which raises 10 times than that normal nonpregnant woman level

11. Cont..
Human chorionic somatomammotropin (hCS), which has mild lactogenic properties which supporting the prolactin
Immediately after the baby is born, the sudden loss of both estrogen and progesterone secretion by the placenta allows the lactogenic effect of the prolactin from mother pituitary gland to assume its natural milk promoting role

12. Regulation of lactation
Suckling
It initiates nerve impules that stimulate the production of oxytocin (OT) in the hypothalamus and its release from the posterior pituitary
Suckling also stimulates the release of prolactin releasing hormone (PRH) from the hypothulamus which stimulates the release of prolactin (PRL) from anterior pituitary
Sight or Sound of the Infant
They cause oxytocin release

13. Cont.. Contraction of Myoepithelial Cells
Oxytocin causes myoepithelial cells of the mammary gland to contract, forcing milk from the gland
Prolactin Stimulates the Resynthesis of Milk

17. Breast milk
Breast milk is the best food for infants the first year. Breast milk is designed to meet the nutritional needs of infants and is easily digested
Colostrum, secreted the first few days after birth, contains antibodies that can protect infants against certain diseases
Higher in protein, minerals, and milk fat but it contains less lactose than milk
Colostrum contains immunoglobulins and growth factors such that a newborn can gain passive immunity

18. Proteins in milk High quality proteins Caseins Milk serum proteins
a-Lactalbumin
b-Lactoglobulin
Immunoglo

19. Casein Make up 80% of the protein of the milk
The mammary gland is the only tissue that synthesizes the caseins
The caseins are responsible for the high calcium content of milk
Caseins are negatively charged and cause calcium to be drawn from circulation to allow secretion of the caseins

20. Lipids in milk
Mixture of mixed triglycerides (> 90%), cholesterol and phospholipids
From two sources
Fatty acids from blood-borne lipoproteins that are diet dependent
Mammary gland synthesis
Relatively high percentage of short fatty acids
Over 500 different fatty acids and their derivatives

21. Sugar in milk Lactose: Glucose + galactose
Glucose is provided from the circulatory system
Glucose is often a limiting factor in milk production
Lactose secretions force water into the mammary gland to maintain osmotic pressure
The mammary gland is the only tissue that synthesizes lactose

22. Factors Controlling Milk Composition
Species and Breading Variation
A major determination of milk composition is the animal species responsible for its synthesis
Seasonal Variation
Milk composition has been observed to fluctuate during winter, summer, and raining season
Number of Milkings
Milk synthesis in a mammary gland is a continues process for the lactation. But once the milk cistern is full, the gland operates its safety values to slow down the rate of synthesis.

23. Cont..
Genetic Factors
Milk composition are likely to be more influenced by gene-controlling phenomenon