King Saud University College of Science Department of Biochemistry Disclaimer The texts, tables, figures and images contained in this course presentation (BCH 376) are not my own, they can be found on: References supplied Atlases or The web Chapter 19 Milk Analysis Professor A. S. Alhomida

2 Mammary Gland Structure

3 Mechanism of Milk Formation 1.Estrogen and progesterone are essential hormones for physical development of breast during pregnancy 2.These hormones inhibit the actual secretion of milk 3.Prolactin is secreted by a mother pituitary gland, and its concentration in her blood raises steadily from the 5 th week of pregnancy until birth of the baby which raises 10 times than that normal nonpregnant woman level

4 4.Human chorionic somatomammotropin (hCS), which has mild lactogenic properties which supporting the prolactin 5.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 Mechanism of Milk Formation, Cont’d

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6 Regulation of Lactation 1.Suckling It initiates nerve impules that stimulate the production of oxytocin (OT) in the hypothalamus and its release from the posterior pituitary 2.and 3 Sight or Sound of the Infant They cause oxytocin release Suckling also stimulates the release of prolactin releasing hormone (PRH) from the hypothulamus which stimulates the release of prolactin (PRL) from anterior pituitary

7 4.Contraction of Myoepithelial Cells Oxytocin causes myoepithelial cells of the mammary gland to contract, forcing milk from the gland 5.Prolactin Stimulates the Resynthesis of Milk Regulation of Lactation, Cont’d

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11 Breast Milk 1.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 2.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 (immunoglobulins are antibodies)

12 Milk Proteins High quality proteins 1.Caseins 2.Milk serum proteins   -Lactalbumin   -Lactoglobulin  Immunoglobulins

13 Caseins 1.Make up 80% of the protein of the milk 2.The mammary gland is the only tissue that synthesizes the caseins 3.The caseins are responsible for the high calcium content of milk

14 Caseins, Cont’d 4.Caseins are negatively charged and cause calcium to be drawn from circulation to allow secretion of the caseins 5.Caseins are the major component of cheese

15 Milk serum proteins 1.Comprise about 18% of the protein component 2.Provide high concentrations of amino acids when digested

16 Lipids 1.Highly variable by species Black rhino have virtually no lipid Seals have approximately. 50% lipid by weight 2.Controlled by Feed type Stage of lactation Species Black Rhino

17 Lipids 1.Mixture of mixed triglycerides (> 90%), cholesterol and phospholipids From two sources Fatty acids from blood-borne lipoproteins that are diet dependent Mammary gland synthesis 2.Relatively high percentage of short fatty acids Over 500 different fatty acids and their derivatives 2.Acetate is important for producing fatty acids Fiber is critical for producing acetate

18 Lipid Milk Composition Lipids (Weight %)CowHumanRat Triglyceride Diglyceride Monoglyceride Trace0.40 Free fatty acid Phospholipils Cholesterol

19 Lactose 1.Glucose + galactose 2.Glucose is provided from the circulatory system 3.Glucose is often a limiting factor in milk production Remember: glucose is made in the ruminant from volatile fatty acids in the liver Liver produces glucose from propionate but is unable to make glucose from acetate Grain concentrates (corn and others) that are broken down into propionate increase glucose in the liver

20 Lactose, Cont’d 3.Lactose secretions force water into the mammary gland to maintain osmotic pressure 4.The mammary gland is the only tissue that synthesizes lactose

21 Milk Composition

22 Different Species Have Different Milk Compositions Why? 1.Composition of milk matches the growth needs of the young of a species rabbit doubles its birth weight in 6 days calf doubles its birth weight in 45 days Rabbit milk has 5 times the protein of cow’s milk Cow’s milk has 2 times the protein of human milk 2.Cows milk needs to have water, iron and Vitamin D added to make it suitable for human infants

23 Factors Controlling Milk Composition 1.Species and Breading Variation A major determination of milk composition is the animal species responsible for its synthesis 2.Seasonal Variation Milk composition has been observed to fluctuate during winter, summer, and raining season

24 3.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. As result, a compositional difference occurs in milk Factors Controlling Milk Composition, Cont’d

25 4.Genetic Factors Milk composition are likely to be more influenced by gene-controlling phenomenon Factors Controlling Milk Composition, Cont’d

26 THE END Any questions?