Milk

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

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

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.  

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

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

The mammary gland

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

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

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

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

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

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

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

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

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

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.

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