MILK COMPOSITION

Leo Timms

Iowa State University

MILK COMPOSITION• Components are similar across species:

- Water - Lactose (CHO) - Proteins

- Lipids(fats) - Minerals - Vitamins

• Component % differ w/in & across species!• Milk is greater than the sum of it’s parts!• Emulsion of fat globules and a suspension

of casein micelles (casein, Ca, P), all suspended in an aqueous phase which contains lactose, whey proteins, minerals, and salts.

MILK COMPOSITION

Lactose, whey,minerals, salts

H20

A. Fully differentiated alveolar epithelial cells characterized by presence of numerous vacuoles (V), rounded basally positioned nuclei (N), abundant cytoplasm, and frequent occurrence of large apically located lipid droplets (F); alveolar lumen is L.

B. Intermediately differentiated alveolar epithelial cells showing fewer cellular vacuoles, more irregularly shaped nuclei, and greater nuclear to cytoplasmic ratio.

C. Undifferentiated alveolar epithelial cells displaying relative absence of cellular vacuoles, highly irregularly shaped nuclei, a mixture of large and small lipid droplets, and very large nuclear to cytoplasmic ratio, (X4,000).

ALVEOLUS

ALVEOLUS

ALVEOLUS

MILK COMPOSITION

Apical membrane

Basementmembrane

MILK COMPOSITION Rat Cow

Nucleus 22 22

RER 15 16

Golgi 21 19

Mito. 7 6

Lipid 1.5 5

Other 33.5 32

MILK COMPOSITION

SECRETION ROUTES

Membrane route

Waterurea

glucoseions

SECRETION ROUTES

Golgi route

Lactosecaseinwhey prot.CitrateCa

SECRETION ROUTESFats

hormonesdrugs

Milkfatroute

SECRETION ROUTES

Transcytosis

SECRETION ROUTES

Tightjunction

Paracellular:between cells

Not commonunless cells disrupted:mastitis!

SECRETION ROUTESMembranerecycling

pH: 6.2-6.9Freeze pt.?< 32F (0C)

MILK COMPOSITION

MILK COMPOSITION

WATER• Highest component except some marine

mammals!• Decreased viscosity so milk can be easily removed from the gland by the neonate• Major source of water for neonates!!!

• No resorbtion in ducts

MILK COMPOSITION

CARBOHYDRATES• LACTOSE

- primary milk CHO in most species- unique to milk

- major osmole in milk- least variable component?

- greatly impacted by mastitis • <1% - >7%: species differences

MILK COMPOSITION

CARBOHYDRATES* mg / 100ml•LACTOSE 5000 (5%)• Glucose 14• Galactose 12•N- acetyl glucosamine 11• Oligosaccharides

LACTOSE

• GLUCOSE is absolutely essential!!!• Can’t be replaced by any other sugar!• Lactose: uses 65-80% of total body glucose in high producing animals• Correlation between milk production and mammary glucose uptake = .93!

WHERE DOES THE GLUCOSE COME FROM?* non ruminants - sugars, digestion of starch

LACTOSE

LACTOSE

LACTOSE

LIVER (glycogen storage)

• Ruminant blood glucose levels 50% of monogas.• 45 - 60% of blood glucose from propionate• glucogenic amino acids, some lower GIT digestion

(Locks glucose in cell)

ATP:not inruminants

NADPH, RIBOSE(fat synth., DNA/RNA)

GLYCEROLmilkfat

LACTOSE• Disaccharide

• Glucose and galactose

• UTP + Glucose UDP- glucose + P-P

• UDP - glucose UDP galactose(epimerase)

• UDP - galactose + glucose lactose + UDP

LACTOSE

LACTOSE• Major enzyme complex: lactose synthase

• Comprised of two enzymes

• Galactosyl transferase(widely present in many cells)

(transfers sugar moeities)

• alpha lactalbumin(specific to the mammary gland!!!)

gene expression increases w/lactogenesismust continually be made: secreted in milk

LACTOSE

Draws in water

LACTOSE

• Milk is always isosmotic with blood!!• Lactose is major osmole but can change!