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
H
2
0

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
Basement membrane

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
Water urea glucose ions
Membrane route

SECRETION ROUTES
Lactose casein whey prot.
Citrate
Ca
Golgi route

SECRETION ROUTES
Fats hormones drugs
Milkfat route

SECRETION ROUTES
Transcytosis

SECRETION ROUTES
Not common unless cells disrupted: mastitis!
Paracellular: between cells
Tight junction

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

MILK COMPOSITION

MILK COMPOSITION
•
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
•
- 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
mg / 100ml
•
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 in ruminants
NADPH, RIBOSE
(fat synth., DNA/RNA)
GLYCEROL milkfat

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/lactogenesis must continually be made: secreted in milk

LACTOSE
Draws in water

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