L1: Composition of Milk and Definitions

Milk Composition

Milk

  • is secreted by the females of all species of mammals
  • to supply nutrition and immunological protection to young
  • interspecies differences in the quantitative composition of milk
  • differences in the metabolic processes of the lactating mother
  • in the nutritive requirements of the suckling young

Analysis of milk

  • only 180 species and data of 50 species are considered to be reliable (sufficient number of samples, representative sampling, principle dairy species and humans

Milk - Definitions

  1. Codex Alimentarius Commission (1999)

    1. the normal mammary secretion of milking animals obtained from one or more milkings without wither addition to it or extraction from it, intended for consumption as liquid milk or for further processing

  2. Code of Federal Regulations (CFR)

    1. is the lacteal secretion, practically free from colostrum, obtained by the complete milking of one or more healthy cows

MILK = word, expression ALWAYS MEANS COWS MILK

e.g. goat milk, sheep cheese - must always have species before

Milk Production

Global

  1. Cow 85%
  2. Water buffalo 11%
  3. Sheep 2%
  4. Goats 2%

Other animals

Camel, yak, reindeer, horse, donkey, dromedary

  • important in some regions
  • insignificant in global trade

Water Buffalo - Bubalus bubalis

10 l/day

7.5% fat

4% protein

4.4% lactose

Sheep - Ovis aries

150 day lactation period

80-1000 l

7.4% fat

5.5% protein

4.8% lactose

Goat - Capra hircus

10 month lactation period

500-1000 l/year g

3.6% fat

3.18% protein

4.3% lactose

NB:

  • goat milk has more easily digestible fat and protein content than cow milk
  • the increased digestibility of protein is important to infant diets (human and animal) as well as to invalid and convalescent diets

Yak - Bos grunniens

200 day lactation period

700 l (900-1200 l)

7-8% fat

5% protein

4.5% lactose

Milk products:

powder, butter, yoghurt, cheese, Kurut (curdled milk which is churned, boiled and then drained)

cream from yak milk = kaimak: thick, sweet, and yellow with a flavour like almonds

yak cheese: hard, Swiss-style cheese that fetches high prices in Kathmandu

Tea is made with yak milk and is a staple part of the diet of Tibetan yak herders

milk is also added to mushrooms to make a mushroom-milk stew

Reindeer - Rangifer tarandus

0.5 l/day df

16-20% fat

10% protein

1.7-1.8% minerals

Cheese:

  • curd is drained and pressed into a flat wooden platter with a rim and placed on fire until the outer layer is toasted
  • the end result is a crispy cheese that resembles bread
  • under the surface it is rich and creamy
  • served at breakfast with jam and a hot beverage

Dromedary - Camelus dromedarium, Camelus bactrianus

750 l per lactation

5.4% fat

3.9% protein

5.1% lactose

Horse - Equus caballus

5 month lactation

2000 l

1.5% fat

2.3% protein

5.7% lactose

From ancient times, the Russian tribes living on the great steppes have been drinking horse milk as a remedy against a whole range of illnesses and to compensate for the meagre nourishment in food derived from their barren surroundings

Milk

  • lacteal secretion
  • particularly free from colostrum
  • obtained by the complete milking of one or more healthy cows, which contains
    • not less than 8.25 MSNF
    • not less than 3.25% milk fat (definition)

Minimum standards in the various states

8.0-8.5% milk-solids-not-fat (MSNF)

3.0-3.8% milk fat

Constituents of Milk

  • water
  • lipids
  • protein
  • carbohydrates
  • salts - minerals
  • vitamins
  • long list of miscellaneous constituents
  • as many as 10^5 different kinds of molecules

Water Content

87.1 human

87.3 cow

86.5 Zebu

82.7 Yak

82.8 Water Buffalo

86.7 Goat

82.0 Sheep

88.8 Horse

66.7 Reindeer

Other Constituents are:

  • dissolved
  • colloidally dispersed
  • emulsified

Dissolved solutes in bovine milk aggregate at around 0.3M and depress freezing point by about 0.54 C

aw = 0.993 (the ratio of its vapour pressure to that of air saturated with water

A small amount of the water in milk is “bound” so tightly by proteins and the fat globule membrane that it does not function as a solvent for small molecules and ions

Milk Proteins

Three main fractions - according to the solubility and different behaviours

  • Casein - separate from milk by acids, rennets
  • Lactalbumin - fractionate salting-out from milk serum
  • Lactoglobulin - fractionate salting-out from milk serum
  • Proteosopepton fraction (proteopepton) fraction = thermoresistent serum proteins

Proteins fall into several classes of polypeptide chains

Caseins - consists of four kinds of polypeptides

  • αs1-, αs2-, β-, κ-, Γ- (Γ- [gamma] proteins are products of β-casein degradation by proteolytic enzymes in milk
  • genetic variants
  • post translational modification
  • product of proteolysis

almost all of the caseins are associated with calcium and phosphate in micelles 20-300 μm in diameter

Whey Proteins

  • α-lactalbumin (0.6-1.7 g/l) - A, B
    • necessary for the synthesis of lactose by its interaction with galactosyltransferase
  • β-lactoglobulin (2-4 g/l) - A, B, C, D, Dr, E, F, G
  • blood serum albumin (0.2-0.4 g/l) - identical to blood serum albumin
  • immunoglobulins (0.5-1.8 g/l)
    • IgG (IgG1, IgG2, IgG fragments)
    • IgM
    • IgA (IgA, secretory IgA)
    • IgE
    • J-chain or component
    • free secretory component

Minor Proteins

  • serum transferrin (iron-binding protein)
  • lactoferrin (iron-binding protein) - among casein, whey, and probably fat globule fraction in the milk and exists as:
    • colourless - iron-free
    • red - iron-containing form (0.12% iron content)
  • β2-microglobulin
  • M1-glycoproteins
  • M2-glycoproteins
  • A1-acid glycoprotein or orosomucoid
  • ceruloplasmin - copper binding protein is a blood serum protein (may be the same as ferroxidase)
  • trypsin inhibitor - in colostrum and first day after parturition, then decreases
  • kininogen - when incubated with trypsin or snake venom, releases a material with a kinin-like ability, causing contraction of smooth muscle
  • folate-binding protein (8 mg/l in cow’s milk)
  • vitamin B12-binding protein

Non-Protein Nitrogen in Milk

  • nitrogen soluble in 12% trichloroacetic acid (TCA)
  • very heterogenous fraction
  • 200-300 mg/l
  • 5-6% of total milk nitrogen
  • transference probably from blood

Technological and Nutritional Significance

  • not known, but amino acids are important
  • nutrition of starter microorganisms, especially for weakly proteolytic strains

Urea:

  • principal component of NPN (6 mmol/l) - strongly correlated with heat milk stability
  • in milk of cows on pasture, urea is twice as high as that from cows on dry feed - heat stability is considerably higher