MILK COMPOSITION

Dr Aneela Hameed
Defination of Milk

 Milk may be defined as the whole, fresh,

clean, lacteal secretion obtained by the
complete milking of one or more healthy
milch animals, excluding that obtained within
15 days before or 5 days after calving or such
periods as may be necessary to render the milk
practically colostrums-free, and containing the
minimum prescribed percentage of milk fat
and milk solid not fat
 MILK
Total Solids
Water

Fat (Lipids) SNF

Emulsion form (50-
100 nm dia.)

Lactose Mineral Other

Nitrogen
(solution form matter constituents
True fat ( 98% TGs Associated Substance
+ MG+ DG+ FFA Substance .01 -1 nm)
PO4, citrates ,
Chlorides of Na, K,
Ca, Mg + traces of
Phospholipids Vitamins Fe, Cu, I etc.
(Lecithin, Cephalin, Cholesterol Carotene
(A,D,E,K)
Sphyngomylin)
•Pigments
•Dissolved Gases
•Vit. C &
Protein B Complex.
Non protein (Suspension, 1-100nm dia.)
•Enzymes etc

Caseins
β Lactglobulin α- Lactalbumin Proteose Peptones
(α,β,γ,κ)
The following terms are used to describe milk
fractions:

 Plasma = milk - fat (skim milk)

 Serum = plasma - casein micelles (whey)
 Solids-not-fat (SNF) = proteins, lactose, minerals,
acids, enzymes, vitamins
 Total Milk Solids = fat + SNF
The residue left when water and gases are
removed is called the dry matter (DM) or total
solids content of the milk
Milk COMPOSITION
• 87.3% water (range of 85.5% - 88.7%)
• 3.9 % milk fat (range of 2.4% - 5.5%)
• 8.8% solids-not-fat (range of 7.9 - 10.0%):
 protein 3.25% (3/4 casein)
 lactose 4.6%
 minerals 0.65% - Ca, P, Mg, K, Na, Zn, Cl, Fe, Cu, sulfate, bicarbonate,
many others
 acids 0.18% - citrate, formate, acetate, lactate, oxalate
 enzymes - peroxidase, catalase, phosphatase, lipase
 gases - oxygen, nitrogen
 vitamins - A, C, D, thiamine, riboflavin, others
Milk can be described as:
 an oil-in-water emulsion with the fat globules
dispersed in the continuous serum phase
 a colloid suspension of casein micelles, globular
proteins and lipoprotein particles
 a solution of lactose, soluble proteins, minerals,
vitamins other components.
Compotition
and
Structure
Composition of milk from various
animals.
Milk Fat
 The milk fat exists as small globules or droplets
dispersed in the milk serum,
 Their diameters range from 0,1 to 20 µm (1 µm =
0,001 mm).
 The average size is 3 – 4 µm and there are some 15
billion globules per ml.
 The emulsion is stabilised by a very thin membrane
only 5 – 10 nm thick (1 nm = 10–9 m ) which
surrounds the globules and has complicated
composition.
The composition of milk fat.
 Composition and structure of milk fat
MEMBRAN
Water
FAT
GLOBULE Protein
Glycerides Phospholipids
triglycerides (the dominating components), Cerebrosides
diglycerides Glycerides
monoglycerides Fatty acids
Fatty acids Sterols
Sterols Other lipids
Carotenoids Enzymes
Vitamins A,D,E,K alkaline phosphatase
Water xanthine oxidase
many others
Cu and Fe
The fat is largely made up of triglycerides, constituting a very complicated
mixture. The component fatty acids vary widely in chain length (2 to 20
carbon atoms) and in saturation (0 to 4 double bonds).

FATTY ACIDS

TRIGLISERIDA
 Fat globules have the
lightest density (mass
per unit volume) at15,5
°C 0,93 g/cm3,
 They tend to rise to the
surface when milk is left
to stand in a vessel.
 The rate of rise follows Stokes’ Law, but the small size
of the fat globules makes creaming a slow process.
 Cream separation can, however, be accelerated by
aggregation of fat globules under the influence of a
protein called agglutinin.
 These aggregates rise much faster than individual fat
globules
 The aggregates are easily broken up by heating or
mechanical treatment.
 Agglutinin is denatured at time-temperature
combinations such as 65 °C/10 min or 75 °C/2 min
and the possibility of aggregation disappears.
PRINCIPAL FATTY ACID IN
MILK
FATTY ACID IN MILK
 Four most abundant fatty acids in milk are myristic,
palmitic, stearic and oleic acids.
 This variation of fatty acids affects the hardness of
the fat.
 Fat with a high content of high-melting fatty acids,
such as palmitic acid, will be hard;
 but on the other hand, fat with a high content of
low-melting oleic acid makes soft butter.
Iodine value
 The iodine value states the percentage of iodine
that the fat can bind.
 Iodine is taken up by the double bonds of the
unsaturated fatty acids.
 Since oleic acid is by far the most abundant of the
unsaturated fatty acids, which are liquid at room
temperature, the iodine value is largely a measure
of the oleic-acid content and thereby of the softness
of the fat.
 The iodine value of butterfat normally varies
between 24 and 46.
Refractive index
 The amount of different fatty acids in fat also
affects the way it refracts light.
 This is a quick method of assessing the hardness of
the fat.
 The refractive index normally varies between 40
and 46.
Amino acids
 The amino acids belong to a group of chemical
compounds which can emit hydrogen ions in
alkaline solutions and absorb hydrogen ions in acid
solutions.
 Such compounds are called amphotery electrolytes
or ampholytes.
 1 Negatively charged in alkaline solutions
 2 Neutral at equal + and – charges
 3 Positively charged in acid solutions
 If the side chain is polar, the water-attracting
properties of the basic and acid groups, in addition to
the polar side chain, will normally dominate and the
whole amino acid will attract water and dissolve in
water. hydrophilic
 A long hydrocarbon chain repels water and makes

the amino acid less soluble or compatible with

water. Hydrophobic
 If there are certain radicals such as hydroxyl (–OH)

or amino groups (–NH2) in the hydrocarbon chain,

its hydrophobic properties will be modified towards
more hydrophilic.
 Hydroxyl groups in the chains of some amino acids
in casein may be esterified with phosphoric acid.
 Such groups enable casein to bind calcium ions or
colloidal calcium hydroxyphosphate, forming
strong bridges between or within the molecules.
 Eight (nine for infants) of the 20 amino acids
cannot be synthesized by the human organism.
 As they are necessary for maintaining a proper
metabolism
 They have to be supplied with the food. They are
called essential amino acids
 All essential amino acids are present in milk
protein.
The electrical status of milk
proteins
 The side chains of some amino acids in milk
proteins carry an electric charge which is
determined by the pH of the milk.
 When the pH of milk is changed by addition of an
acid or a base, the charge distribution of the
proteins is also changed.
 Cow milk proteins
Concentration g/kg %
Total proteins 33.0 100.0
Total caseins 26.0 79.5
s1-casein 10.0 30.6
s2-casein 2.6 8.0
-casein 9.3 28.4
-casein 3.3 10.1

Whey proteins 6.3 19.3

-lactalbumin 1.2 3.7
-lactoglobulin 3.2 9.8
Bovine Serum Albumin 0.4 1.2
Immunoglobulins 0.7 2.1
Other (proteoses peptones)
- 0.8 2.4
Proteins of fat globule membrane 0.4 1.2
 Milk proteins (30 - 35 g/l)

Minor proteins Enzymes

Caseins Soluble proteins
(24 - 28 g/l) (5 -7g/l)
(70 - 80%) (15 - 20%)

 Lactoglobulins Serum albumin

(2 - 4 g/l) (0.1 - 0.4 g/l)

 Caseins  Caseins
(15 - 19 g/l) (3 - 4 g/l)  Lactalbumin (2 to 5 %)
(1 - 1.5 g/l)

 Caseins Immunoglobulins
(9 - 11 g/l) (0.5 - 1 g/l)

Proteose
Caseins
Peptone
(1 -2 g/l)
(0.5 - 1.8g/l)
Swaisgood (1982)
CASEIN
Protein
MICELLE
Casein
Proteose pepton
Salts
Ca
Phosphate
Citrate
K, Mg, Na
Water
Enzymes (lipase, plasmine)
Composition of casein micelles
 93 % caseins : 4 phosphoproteins
 s1-CN : 36 %
 s2-CN : 10 %
 -CN : 34 %
 -CN : 12 %
 7 % : colloidal mineral complex containing
phosphate, calcium, magnesium and citrate
In milk the whey proteins are in colloidal solution
and the casein in colloidal suspension.
Casein

 Casein is a group name for the dominant class of

proteins in milk.

 The caseins easily form polymers containing

several identical or different types of molecules.

 Abundance of ionisable groups and hydrophobic

and hydrophilic sites the molecular polymers
formed.
Casein micelles.
 The polymers are built up of hundreds and
thousands of individual molecules and form a
colloidal solution
 These molecular complexes are known as casein
micelles.
 Such micelles may be as large as 0.4 microns, and
can only be seen under an electron microscope

 A medium-sized micelle consists of about 400 to

500 sub-micelles which are bound together
 Subgroups of casein
 The three subgroups of casein, αs-casein, κ-casein
and β-casein,
 All heterogeneous and consist of 2 – 8 genetic
variants.
 Genetic variants of a Protein differ from each other
only by a few amino acids.
 The three Sub- Groups have in common the fact that
one of two amino acids containing hydroxy groups
are esterifies to phosphoric acid.
 The phosphoric acid binds calcium and magnesium
and some of the complex salts to form bonds between
and within molecules.
Casein micelles
Colloidal solubilisation of casein micelle
 The content of α-, β- and κ-casein is
heterogeneously distributed in the different
micelles.
 Calcium salts of αs-casein and β-casein are al-
most insoluble in water, while those of κ-casein are
readily soluble.
 Due to the dominating localisation of κ-casein to
the surface of the micelles, the solubility of calcium
κ-caseinate prevails over the insolubility of the
other two caseins in the micelles,
 So whole micelle is soluble as a colloid.
 The α- and β-caseins are mainly concentrated in the
middle of the sub-micelles, while κ-casein
predominates on the surface.
 The hydrophilic protruding chain of the κ-casein

protrudes from the surface of the sub-micelles

forming a hairy layer ( 5 – 10 nm).
 The κ-casein-deficient sub-micelles are

mainly located in the centre of the micelle,

 whereas the κ-casein-rich sub-micelles predominate
on the surface, giving the whole micelle a hairy
surface layer.
 The hairy layer of the κ-casein’s protruding chain is
partially responsible for the micelle’s stability
through a major contribution to the negative charge
of the micelles
 The calcium phosphate and hydrophobic
interactions between sub-micelles are responsible
for the integrity of the casein micelles.
 Adding an excess of Ca and phosphate results in
aggregation of sub-micelles into larger units –
micelles.
 The reason for this aggregation is presumably the
deposition of Ca-phosphate in the sub-micelles,
which lowers their electric charge and makes them
more compact.
Casein curd
 If the hairy layer is removed, e.g. by acid addition or
rennet – induced hydrolysis, the colloidal stability of
the micelle is destroyed and the micelles coagulate or
precipitate.
 In an intact micelle there is surplus of negative
charges, therefore they repel each other.
 Water molecules held by the hydrophilic sites of k-
casein form an important part of this balance.
 When the hydrophilic sites are removed, water will
start to leave the structure.
 This gives the attracting forces room to act
Casein curd
 New bonds are formed, one of the salt type, where
calcium is active, and the second of the
hydrophobic type
 These bonds will then enhance the expulsion of
water and the structure will finally collapse into a
dense curd.
Low temperature effect on β-casein
 The micelles are adversely affected by low temperature
 β-casein chains start to dissociate and the CCP leaves
the micelle structure, where it existed in colloidal form,
and goes into solution.
 The explanation of this phenomenon is that β-casein is
the most hydrophobic casein and that the hydrophobic
interactions are weakened when the temperature is
lowered.
 The loss of CCP causes a weaker attraction between
sub-micelles and individual casein molecules in the
sub-micelles.
 β-casein is then also more easily hydrolysed by
various proteases
 Hydrolysis of β-casein to γ-casein and proteose-
peptones means lower yield at cheese production
because the proteose-peptone fractions are lost in
the whey.
 The breakdown of β-casein may also result in
formation of bitter peptides, causing off-flavour
problems in the cheese.
Precipitation by casein
 One characteristic property of casein is its ability to
precipitate.
 Due to the complex nature of the casein molecules,
and that of the micelles formed from them,
precipitation can be caused by many different
agents.
Precipitation by acid
 The pH will drop if an acid is added to milk or if acid-
producing bacteria a allowed to grow in milk. This will
change the environment of the casein micelles in two
ways.
1. Firstly colloidal calcium hydroxyphosphate, present
in the casein micelle, will dissolve and form ionised
calcium, which will penetrate the micelle structure and
create strong internal calcium bonds.
2. Secondly the pH of the solution will approach the
isoelectric points of the individual casein species
 Both methods of action initiate a change within the
micelles.
 Growth of the micelles through aggregation and
ending with a more or less dense coagulum.
 The isoelectric points of the casein components
depend on the ions of other kinds present in the
solution.
 Theoretical values, valid under certain conditions,
are pH 5.1 to 5.3.
Precipitation by enzymes
 The amino-acid chain forming the κ-casein
molecule consists of 169 amino acids.
 From an enzymatic point of view the bond
between amino acids 105(phenylalanin) and 106
(methionin) is easily accessible to many
proteolytic enzymes.
 The soluble amino end contains amino acids 106 to
169, which are dominated by polar amino acids
and the carbohydrate, which give this sequence
hydrophilic properties.
 This part of the κ-casein molecule is called the
glycomacro-peptide and is released into the whey in
cheesemaking.
 The remaining part of the κ-casein, consisting of amino
acids 1 to 105, is insoluble and remains in the curd
together with αs- and β-casein.
 This part is called para-κ-casein.
 The formation of the curd is due to
1. Sudden removal of the Hydrophilic Macropeptides
2. Imbalance in intermolecular forces.
 Bonds between hydrophobic sites start to develop and
are enforced by calcium bonds which develop as the
water molecules in the micelles start to leave the
structure.
 This process is usually referred to as the phase of
coagulation and syneresis.
 The splitting of the 105 – 106 bond in the κ-casein
molecule is often called the primary phase of the
rennet action,
 while the phase of coagulation and syneresis is referred
to as the secondary phase.
 There is also a tertiary phase of rennet action,
where the rennet attacks the casein components in a
more general way. This occurs during cheese
ripening.
 The durations of the three phases are determined
mainly by pH and temperature.
Whey proteins
 Whey protein is the name commonly applied to
milk serum proteins.
 they are not precipitated at their isoelectric points.
 They are, precipitated by polyelectrolytes such as
carboxymethyl cellulose.
 When milk is heated, some of the whey proteins
denature and form complexes with casein, thereby
decreasing the ability of the casein to be attacked
by rennet and to bind calcium.
α-lactalbumin
 Whey proteins in general, and α-lactalbumin in
particular, have very high nutritional values.
 Their amino acid composition is very close to that
which is regarded as a biological optimum.
 α - Lactalbumin contains 123 amino acids and
represents about 25% of the serum proteins in milk
α-lactalbumin
Primary structure
 The amino acid sequence is very similar to lysozyme

and so is the three dimensional structure.

 They have totally different activities and do not interfere
with each other when present in the same system.
 The protein has a very compact, globular structure
that is nearly spherical in shape.
Physical and Chemical Properties

 a. Molecular weight= 14,200

 b. Phosphorus content-none

 c. Sulfhydryl and disulfide bonds-4

intramolecular disulfide bonds and no free

sulfhydryl groups.
 d. Self-association reactions-at low pH α-

Lactalbumin will denature and undergo self

association reactions.
 e.Heat stability-α-Lactalbumin is the most heat stable
serum protein in milk. 50% of the α-Lactalbumin will
not be denatured even after 30 minutes of heating at
77oC.

 f. Biological function-α-Lactalbumin is necessary for

lactose synthesis. If no α-Lactalbumin is present in
the golgiapparatus, no lactose could be synthesized.
β-lactoglobulin
 β - Lactoglobulin contains 162 amino acids.
 It is the major milk serum protein. It is about 50%
of the serum protein and 8% of the protein in milk.
 There is no β -Lactoglobulin present in human
milk.
 β - Lactoglobulin can be irreversibly denatured by
heat.
 This stress causes rupture of intramolecular
disulfide bonds and precipitation
Physical and Chemical Properties

 a. Molecular weight 18,362

 b. Phosphorus content -none
 c. Sulfhydryl and disulfide groups -one free SH
group and 2 intramolecular disulfide bonds 66 to
160 and 106 to 119 or 106 to 121.
 If milk is heated to over 60 °C, denaturation is initiated
where the reactivity of the sulphur-amino acid of β-
lactoglobulin plays a prominent part.
 Sulphur bridges start to form
1. between the β-lactoglobulin molecules,
2. between β-lactoglobulin molecule and K-casein
3. between β-lactoglobulin and α-lactalbumin.
 At high temperatures, sulphurous compounds such as
hydrogen sulphide are gradually released.
 These sulphurous compounds are responsible for the
“cooked” flavour of heat treated milk.
Immunoglobulins and related minor
proteins
 Immunoglobulins are antibodies synthesised in
response to stimulation by specific antigens.
 They are specifically present in blood.
 Their content in cows’ milk is low, but some of
them are present in higher levels in colostrum and
human milk.
 They can also act against “particles” such as
bacteria, viruses and even fat globules, and
flocculate them, a reaction called agglutination
Serum albumin
• Comes from blood
• Role in the transport of bile salts, fatty acids
Membrane proteins
 Membrane proteins are a group of proteins that
form a protective layer around fat globules to
stabilise the emulsion

 Some of the proteins contain lipid residues and are

called lipoproteins.
Denatured proteins
 As long as proteins exist in an environment with a
temperature and pH within their limits of tolerance,
they retain their biological functions.
 If they are heated to temperatures above a certain
maximum their structure is altered.
 The same thing happens if proteins are exposed to
acids or bases, to radiation or to violent agitation.
 The proteins are denatured and lose their original
solubility.
Milk Enzymes
 Enzymes in milk occur in various states:
 (1) as unassociated forms in solution,
 (2) associated or an integral part of membrane
fractions, such as the fat globule membrane
 (3) associated with casein micelles,
 (4) as part of the microsomal particles.
 The origin of these enzymes in milk is from:
 cow’s udder (synthesized enzymes)
 or from bacterial enzymes (bacterial source).
PLASMIN
 This enzyme hydrolyzes proteins.
 Limited proteolysis of B-casein by this enzyme is responsible
for the presence in milk of large polypeptides derived from
this protein, known as the gamma-caseins.
 Activity of this enzyme is also important in cheese ripening
and the stability of casein micelles in various products such as
UHT milk.
 Nearly, 80% of its proteolytic activity is lost when milk is
pasteurized.
 Microbial derived proteases are more heat stable than native
 proteases in milk and they tend to survive even UHT
processing.
Lactoperoxidases
 Peroxidase transfers oxygen from hydrogen
peroxide (H2O2) to other readily oxidisable
substances.
 This enzyme is inactivated if the milk is heated to
80°C for a few seconds,
Catalase
 Catalase splits hydrogen peroxide into water and free
oxygen.
 By determining the amount of oxygen that the enzyme
can release in milk, it is possible to estimate the catalase
content of the milk and learn whether or not the milk has
come from an animal with a healthy udder.
 Milk from diseased udders has a high catalase content,
while fresh milk from a healthy udder contains only an
insignificant amount.
 Catalase is destroyed by heating at 75 °C for 60 seconds.
Phosphatase
 Phosphatase split certain phosphoric-acid esters
into phosphoric acid and the corresponding
alcohols.
 Phosphatase is destroyed by ordinary Pasteurisation
(72 °C for 15 – 20seconds), so the phosphatase test
can be used to determine whether the Pasteurisation
temperature has actually been attained.
 The phosphatase test should preferably be
performed immediately after heat treatment.
Lipase
 Lipase splits fat into glycerol and free fatty acids. Excess free
fatty acids in milk and milk products result in a rancid taste.
 The action of this enzyme seems, in most cases, to be very weak,
though the milk from certain cows may show strong lipase
activity.
 The quantity of lipase in milk is believed to increase towards the
end of the lactation cycle.
 Lipase is, to a great extent, inactivated by pasteurisation, but
higher temperatures are required for total inactivation.
 sodium and magnesium tend to stimulate the lipase activity,
while calcium and magnesium show an inhibitory effect.
 Mineral composition (total and soluble) of milk
[Total] – [Soluble] = [Micellar] or [Colloidal]

Mineral Concentration (mg/kg)

Total calcium 1250
Soluble calcium 350
Total magnesium 115
Soluble magnesium 70
Total sodium 425
Soluble sodium 400
Total potassium 1600
Soluble potassium 1500
Total chloride 1100
Soluble chloride 1100
Total phosphorus 950
Soluble phosphorus 420
Total inorganic phosphate (in phosphorus) 720
Soluble inorganic phosphate (in phosphorus) 300
Total citrate 1650
Soluble citrate 1500
Partition of Major Minerals in Colloidal and
Soluble Phases (% of Total Minerals)
Carbohydrates in milk : two types

 Free
• lactose
• glucose
• galactose
• N-acetylated glucose
• N-acetylated galactosamine
 Linked to proteins
• glycoproteins
 -casein
• Lactoferrin
• Lactoperoxidase
 Disaccharide composed of one glucose unit and
one galactose unit
 Major sugar of the most milks from different
mammals
 Lactose is one of the least soluble of the common
sugars, having solubility in water of only 17.8% at
25◦C
 Cow and human milks contain about 4.8 % and 7
% of lactose respectively
 When lactose undergoes dehydration to form
lactulose. It stimulates the growth of
Bifidobacterium bifidum and is thus beneficial in
establishing healthy commensal microbiota in the
gut.
 Lactose is a good source of energy and may
promote calcium absorption.
 Digestion of lactose presents a problem in some
people as they lack beta-d-galactosidase enzyme in
their GIT.
 Consequently, dietary lactose is not hydrolyzed
and reaches colon where it is metabolized by
colonic bacteria forming gases (methionine and
hydrogen).
 Accumulation of gas leads to discomfort caused by
bloating and diarrhea.
 Such lactose malabsorption is aggravated by yogurt
containing live cultures,
 the culture furnishes the lactose-hydrolyzing
enzyme beta-d-galactosidase and normal digestion
pattern is restored.
 Sweet value of lactose

• Sucrose : 100
• Fructose : ~ 150
• Glucose : ~ 75
• Maltose : ~ 40
• Galactose : ~ 35
• Lactose : ~ 20

Low sweet value of lactose compared to other sugars

Role of lactose in milk and dairy products

 Contribute to the nutritive value of milk and dairy products

Essential component for the fermentation of some dairy products
(yoghurts, cheeses, …)
 Affects the texture of some concentrated and frozen products
(viscosity, cristals, …)
During rapid drying,amorphous lactose is formed. This form of
lactose is very hygroscopic and causes caking in dried products
containing moisture levels of 8% or more.
 Participate to the color and flavor changes of dairy products
during heat treatments and storage (Maillard reaction)
Food Applications

 Infantile food
 Glazing, prevent crystallisation of other sugars in mixture, ...
(confectionery - bakery)
 Appearance and taste of bakery products, fried foods...
(Maillard)
 Exhauster of taste (sauces, french dressing,...)
 Stabiliser of aroma
 Agent of encapsulation (confectionery
Vitamins in milk
 Vitamins are organic substances that occur in very
small concentrations in both plants and animals.
 They are essential to normal life processes, but
cannot be synthesised by the body.
 Among the best known vitamin in milk are A, the
vitamin B group, vitamin C and D.
Vitamins in Bovine Milk
Physical properties of milk
1. Appearance
 the opacity of milk is due to its content of

suspended particles of fat, proteins and certain

minerals.
2. Colour
 Milk is a liquid of yellow white colour .
 Colour varies from bluish white to light yellow,
depending upon the breed of the cow, the feed fed to
the cow, and the quantity of fat and other solids
present in it
 Cows milk is yellow white & that of buffalo, sheep,
goat and other Species is white.
 Yellow colour of the milk is due to a pigment known
as carotene which is synthesized from the green feed
fed to the cow
 Conversion of carotenes into Vit.A

 Chiefly occurs in liver.

 In case of buffalo this change is complete and thus buffalo
milk is white.
 In case of cows this conversion of carotene into Vit.A is
partial so cows milk is yellow in color.
 The white colour (opalescence) of milk is due to reflection
of light by the colloidal protein (Casein), calcium
caseinate & phosphate and the fat globules
 The bluish Colour of separated milk or whey is due to
another pigment known as Riboflavin (Vit.B2) or
Lactochrome.

3. Taste
 Milk is slightly sweet in taste. This is due
to the presence of lactose (Milk Sugar) in
it.
 The Sweet taste of lactose is balanced
against the salty taste of chloride in Milk.
4. Smell
 Milk has got a characteristic odour of its own,
when it is drawn from the udder.
 Freshly drawn milk has a “cowey” odour which disappears
when kept exposed for some time
 Milk has got the capacity to acquire odour from the
surrounding and also from the feed etc. but these odours are
abnormal.
 Milk develops odours due to bacterial action and change in
its chemical composition
 Certain metals may have an adverse effect on the flavour of
the milk which comes in contact with them (copper, and
copper alloys, nickel, brass, bronze etc)
 Rusty cans or other rusty surfaces may prove harmful
producing a metallic &other objectionable flavors.
5. Osmotic pressure
 Osmolality is a measure of the total number of
dissolved particles in a given volume of solution
given in osmol/KJ.
 Osmotic pressure is controlled by the number of
molecules or particles, not the weight of solute;
thus 100 molecules of size 10 will have 10 times
the osmotic pressure of 10 molecules of size 100
6. Freezing point
 The freezing point of milk is lower than that of
pure water due to the dissolved components such as
lactose and soluble salts.
 The freezing point of milk is the only reliable
parameter to check for adulteration with water.
 The freezing point of milk from individual cows
has been found to vary from –0.54 to –0.59°C.
 Adulterated milk will show increased freezing
point due to lower molal concentration of lactose
and salts.
 The freezing point is affected by :
~Increased acidity (Decrease FP)
~addition of preservatives (Decrease FP)
~addition of water (Increase FP)
 Skim, whole milk or cream have same FP
7. Boiling Point
 The boiling point of milk is higher than that of pure
water due to dissolved components.
 The boiling point of milk is 100.17◦C.
 Milk is slightly heavier than water because of its
solute content and boiling point of a liquid is
influenced by factors responsible for its Sp.gravity.
8. Density
 Milk density at 20◦C ranges from 1.027 to 1.033
with an average of 1.030 g/cm3
 Temperature affects density because milk expands
when heated and so it becomes less dense as
temperature rises
Density formula
9. Specific Gravity
 It is the ratio of the mass of a solution or a substance
to the mass of a similar volume of water.
 Fresh whole milk has specific gravity in range of
1.030–1.035, with an average of 1.032.
 The specific gravity of freshly drawn milk is lower
than sp. Gravity obtained, after an hour or later.
 The sp. gravity .of a fluid varies with its temperature.
10. Acid base Equilibrium

 Freshly drawn milk has got “Amphoteric Reaction” i.e. it

changes red litmus blue and blue litmus red.
 Its average pH value is 6.7
 On titrating it with an alkali it is found to contain 0.1 to
0.17% acidity.
 This acidity is not due to lactic acid (Developed) but due
to phosphates of milk proteins, Citrates and carbon dioxide
present in milk (Natural).
11. Viscosity

 It is the resistance to flow and is the reverse of fluidity.

Viscosity is the property of all fluids. It can be expressed
in only relative terms and for convenience the relative
viscosity of any fluid is compared with water.
 Water flows with ease .Syrup and honey pour much more
slowly and posses greater viscosity.
 Milk is 1.5 to 1.7 times more viscous than water owing to
the presence of solids in milk.
 Heating the milk to pasteurization
temperature or agitating it lowers the
viscosity.
12.Adhesiveness of milk
 A piece of paper moistened with milk
sticks to a flat surface of wood, glass or
metal. This property is undoubtedly due to
casein, which is used in large quantities in
the manufacture of casein glue, one of the
strongest glues made.
FACTORS AFFECTING
COMPOSITION
 1. Species
 2. Breed
 3. Individuality
 4. Interval of milking
 5. Completeness of milking
 6. Frequency of milking
 7. Irregularity of milking
 8. Day-to-day milking
 9. Diseases and abnormal conditions