Milk

Objectives Formation of milk (lactation) Nutritional Value of milk Composition of milk Human milk and animal milk The colostrum

Lactation Preparation of breast during pregnancy: carried out by the ovarian and placental hormones (estrogen & progesterone mainly) Initiation of milk secretion : Under the effect of lactogenic hormone (from ant. Pituitary), starts at the last days of pregnancy due to lowering of hormones (where prev. hormones inhibit releasing of the lactogenic hr.) Milk letting: Flow of milk from breasts occurs after delivery by the suckling reflex and release of oxytocin (post. Pituitary) Formation of milk is an active secretory process that occurs in three successive processes:

Nutritional Value of Milk : Almost complete diet for infant Deficient in : vit K , C + Fe , Cu 3 rd m citrus fruit 6th m soup ,egg yolk

Color White ± yellowish ,opaque carotenes( colostrum + cow’s milk) Emulsion of fat + colloidal state of proteins & Ca phosphate

Reaction pH cow’s 6.6 ,human milk 7.0 Good buffer( proteins ,HCO3-, PO4,) Used for hyperacidity

Composition of milk Lipids Proteins Carbohydrate Minerals and vitamins

Milk Fat Human & cows about 3.5% Present in form of emulsion surrounded by a thin coat layer of (PL, cholesterol and proteins) TAG: 99 %, main palmitic, oleic, stearic acids Human milk 10% essential. F.A. Cow’s milk 10% butyric acid

Other lipids : Rich in vit. A Poor in vit. K fair in E Small amount of cholesterol, phospholipids, fat soluble vit. & carotenes Rich in vit. A Poor in vit. K fair in E Cow’s milk poor in D but human fair

Casien : 80% (cow’s),40% (human) , Milk Proteins Human 1.2% , cow’s 3.5% Casien : 80% (cow’s),40% (human) , phosphoprotein, Rich in methionine, Poor in cystine & cysteine Ppt at its pI (4.6) Not coagulable The rate of growth of newborns of different species of animals depend on a greater extent upon the ratio of proteins in their milk

Lactalbumin & Lactoglobulin (whey protein) Human 60% , Cow 20 % Separate in whey Heat coagulable High biological value Can’t ppt at pH 4.6 Include Ɣ –globulin (ab.)

Other proteins Lactoferrin: ↑↑↑↑ absorption of iron in intestine Contain enzymes e.g. proteinases, amylase, peroxidase, catalase, alkaline phosphatase

Lactose (most suitable sugar) Only CHO in milk Human 7.4% , cow’s 4.7% Digestion : gives glucose + galactose for E Galactose can form glycolipids Less sweet: not nausea Helps growth of lactic acid- producing bacteria in the intestine

↑ solubility & absorption of Ca , Mg 2, PO4 , Fe, Cu Bacteria Lactose Lactic acid ↓pH ↑ solubility & absorption of Ca , Mg 2, PO4 , Fe, Cu Inhibits growth of putrefactive bacteria

Milk Minerals & Vitamins Human less in minerals than cow’s Rich in Ca , PO4 , K, Cl Fair amn. of Na & Mg Both milk poor in Fe & Cu but human is richer Rich in vit A & B2 Poor in C & K Fair in others

Comparison Between Human & Animal Milk Hman Milk Animal Milk 1- Proteins: Amount of curds Types of curds small fine and thin Large Thick and tough 2-Fats: Fat globules Volatile acids Small size Absent High amounts 3- Carbohydrate Lactose 4-Minerals: Ca: P content Ca:P ratio Iron Smaller Suitable 2:1 Deficient Higher Not suitable More deficient 5- Reaction Alkaline(7.0) More acidic (6.6) 6- Digestion Easy Difficult 7-Growth promotion More Less Fine and thin curds are easier to digest Large amounts of volatile fatty acids render animal milk irritant to gastric mucosa Large size of fat globules interfere w their adequate digestion

Colostrum Yellowish secreted during the first week Differs from mature in: Higher protein with less casein & more whey protein Esp rich in IgA which prevents gastroenteritis Minerals are higher Vitamins are higher

Fats are lower but with higher fat soluble vitamins, carotenes (yellowish color ) Easier to digest Lower lactose , less sweet & more suitable for new born

Some Milk Products Full cream milk :milk containing all of its fat e.g. nestogen, SMA and SIMILAC Acidified milk: milk with pH lower than ordinary milk and is used in infants suffering from diarrhea or vomiting e.g. Pelargon and prodieton Fortified milk: milk to which concentrated forms of vitamins or minerals are added

Milk Clotting Rennin Casein paracasein (sol) +peptone –like Paracasein + Ca 2+ insoluble Ca para. ppts entangling fat + fat soluble vit. milk clot or cheese

greenish yellow (riboflavin) in color contains Whey : greenish yellow (riboflavin) in color contains water & water soluble vitamins, lactalbumin, lactaglobulins, lactose, minerals, reduced Ca content

Milk Curdling It is the precipitation of casein at its isoelectric pH, (pH =4.6) Produced by the action of lactobacillus acidophilus Fermenting lactose Casein ppts + fats + fat soluble vit. to form curds or yogurt

Whey of the milk curds contains less lactose more B- vitamins( produced by bact.) more calcium (not ppt with casein)

Advantages of colostrum for baby Highly nutrititve: high proteins and minerals High antibody contents; mainly gamma globulins which give immunity Laxative effect : which prevents constipation