This is for Education purpose only by Anjali P

1. DAIRY SCIENCE TECHNOLOGY
SUBMITTEDBY
ANJALIP
II MScZOOLOGY
192ZO007
SUBMITTEDTO
DR. J. ROOPAVATHY
ASSISTANTPROFESSOR
NIRMALACOLLEGEFORWOMEN,COIBATORE

3. SL
NO.
Contents
1. Introduction
• Milk Proteins; casein and whey
protein
2. Influence of Heat Treatment on Milk
leads to the Casein - Whey Protein
Interaction.
3.

4. MILK PROTEINS
 Milk contains 3.3% total protein.
 Milk proteins contain all 9 essential amino acids
required by human diet.
Milk proteins are synthesized in the mammary
gland, but 60% of the amino acids used to build the
proteins are obtained from the cow's diet.

5.  There are 2 major categories of milk protein.
I. Casein
II. Whey or Serum Protein.
 In cow's milk, approximately 82% of milk protein is casein
and the remaining 18% is serum, or whey protein.

6. • CASEIN : The casein family contains phosphorus
and will coagulate or precipitate at pH 4.6.
• The casein family of protein consists of several types
of caseins (α-s1, α-s2 , ß, and k) and each has its own
amino acid composition, genetic variations, and
functional properties.
• The caseins are suspended in milk in a complex
called a micelle

7. • WHEY OR SERUM : The serum (whey) proteins do not
contain phosphorus, and these proteins remain in
solution in milk at pH 4.6.
• The serum (whey) protein family consists of
approximately 50% ß-lactoglobulin, 20% α-lactalbumin,
blood serum albumin, immunoglobulins, lactoferrin,
transferrin, and many minor proteins and enzymes.
• Whey proteins do not contain phosphorus, by definition,
but do contain a large amount of sulfur-containing amino
acids.

8. • Caseins and whey proteins co-exist in fresh milk, but do
not interact.
• Both have specific nutritional and functional properties.
The whey proteins are a readily digestible source of
branched-chain amino acids, whereas the caseins are
slowly digested and are essential in the transport of
calcium phosphate.
• Likewise, the caseins are crucial in cheese making,
whereas the whey proteins possess unique heat gelation
properties. Casein-whey protein interactions can occur as
a result of heat treatment.

9. • These interactions can provide highly desired
functionality of milk proteins, e.g., for the structure and
stability of yoghurt, heat stability or foaming.
• Whey protein denaturation and casein-whey protein
interactions can also be induced through non-thermal
technologies, such as high pressure treatment.
• The heat-induced casein-whey protein interactions,
considering the factors influencing the interactions and
their effect on the functional properties of milk proteins.

10. Influence of Heat Treatment on Milk leads to the Casein -
Whey Protein Interaction.
• The caseins are stable to heat treatment. Typical high
temperature short time (HTST) pasteurization
conditions will not affect the functional and nutritional
properties of the casein proteins.
• High temperature treatments can cause interactions
between casein and whey proteins that affect the functional
but not the nutritional properties. For example, at high
temperatures, ß-lactoglobulin can form a layer over the
casein micelle that prevents curd formation in cheese.

11. • The whey proteins are more sensitive to heat than the caseins.
HTST pasteurization will not affect the nutritional and
functional properties of the whey proteins.
• Higher heat treatments may cause denaturation of ß-
lactoglobulin, which is an advantage in the production of
some foods (yogurt) and ingredients because of the ability of
the proteins to bind more water.
• Denaturation causes a change in the physical structure of
proteins, but generally does not affect the amino acid
composition and thus the nutritional properties.

12. Casein-whey protein interactions are detrimental in
(rennet-) cheese making, whereas the presence of
aggregates in the serum phase during yoghurt making
improves gelation properties and strengthens gel texture;
micelle-bound aggregates increase the heat stability of
milk, particularly in concentrated systems. The current
knowledge and a strict control of the processing conditions
create functionality of the dairy proteins that covers a very
broad range of applicability.

13. Caseins have relatively little secondary and tertiary
structure. As a result, caseins have what is sometimes
referred to as a natively-unfolded structure and specific
amino acids are rather easily accessible for interactions. On
the other hand, the high degree of secondary and tertiary
structure of whey proteins results in a tightly-folded and
poorly-accessible structure at ambient temperature

14. However, increasing temperature results in the
denaturation of whey proteins, which involves the
following steps :
 Dissociation of the β-Lg dimers into monomers;
 Unfolding of the globular protein structure and
exposure of the reactive free thiol group of β-Lg and the
2 and 4 disulphide bridges in β-Lg and α-La,
respectively;
 Aggregation via thiol-thiol oxidation and thiol-
disulphide interchange reactions.
In this last step, casein-whey protein interactions occur.

15. • β-Lg is the main source of free thiol groups in milk and
drives these interactions.
• The free thiol group of β-Lg can interact with disulphide
bonds of other b-Lg molecules or other whey proteins,
• E.g., α-La, but also with αs2-casein (αs2-CN) and K-casein
(K-CN), which can thus participate in thiol-disulphide
interchange reactions.
• The location of K-CN on the casein micelle surface makes
it readily accessible for interactions with denatured whey
proteins.

16. • Although α-La is not believed to directly interact with K-
CN, it is also found in the whey protein-K-CN
aggregates, along with β-Lg.
• K-CN-whey protein complexes are found in heated milk
on the surface of the casein micelles, but also in the
serum phase of the milk.
• The distribution of these complexes between the casein
micelles and the serum depends on many factors,
including heating time and temperature, milk pH and
the salt composition.

17. Schematic representation of the effect of skim milk
pH(A, D – pH 6.5; B, E – pH 6.8; C, F – pH 7.1) on the
distribution of whey protein (WP) aggregates between
the serum phase and the casein (CN) micelles in skim
milk heated for 30 min at 90°C (A, B, C – unheated skim
milk; D, E, F – heated skim milk), based on data from
Crowley et al.
CASEIN MICELLE
WHEY PROTEIN

18. • Functional properties of milk, such as gelation, heat
stability and foaming can be tailored by controlling the
casein-whey protein interactions.
• The fraction of denatured whey proteins associated with
the casein micelles strongly depends on several factors, e.g.,
pH and the salt composition of the milk serum.
• When milk is heated at its natural pH, i.e., 6.6-6.7, part of
the denatured whey proteins is associated with the casein
micelles and part of the denatured whey proteins is found
in the milk serum (9,10).

19. • When the pH of the milk is lowered prior to heating, e.g.,
to 6.3-6.5, the level of denatured whey protein associated
with the casein micelles increases.
• Conversely, at higher pH, the level of denatured whey
protein associated with the casein micelles decreases.

21. • The K-CN distribution follows similar trends
(9,10).
• After heat treatment of milk at low pH, virtually all
K-CN is associated with the casein micelles,
whereas after heat treatment at high pH, a
considerable proportion of K-CN is found in the
milk serum, mostly associated with denatured
whey proteins.

22. Casein-whey protein interactions have a strong influence on
some functional properties of milk, which may either be
positive (e.g., for yoghurt or heat-stable products) or negative
(e.g., for cheese). The negative impact for rennet-coagulated
cheese variants like Gouda, Cheddar or Mozzarella is found on
the enzymatic coagulation of milk, where K-CN is hydrolyzed
by chymosin, after which the para-casein micelles form a gel.

23. Schematic representation of the
influence of whey protein (WP) –
casein (CN) interactions on the
rennet-induced hydrolysis of κ-
CN with formation of
glycomacropeptide (GMP) and
aggregation of the casein micelles
(A, B –skim milk, containing
native whey proteins; C, D – high-
heat skim milk, containing serum
and micellar whey protein
aggregates; A, C – skim milk prior
to rennet hydrolysis; B, D – skim
milk following rennet hydrolysis).

24. Yogurt making
• Acid-induced coagulation forms a crucial step in the
manufacture of yoghurt and other acid coagulated dairy
products, like quark, cottage cheese and cream cheese.
• Preheating milk is a crucial step in attaining a desirable
yoghurt texture. Without preheating a weak texture is
obtained, or large amounts of additional milk protein
need to be added to achieve the desired texture, which
is undesired economically, unless protein fortification
is the specific aim.

25. • As a result of preheating, coagulation of milk during
fermentation commences at a higher pH, through
aggregation of the denatured whey proteins, which
occurs in the pH region 5.5-5.2.

26. Schematic
representation of the
possible effect of heat
induced whey protein
(WP) aggregate
distribution (B, D – on
the surface of the casein
(CN) micelles; C, E – in
the serum phase) on the
mechanism of acid
gelation of skim milk (A
– unheated milk; B, C,

27. • The pH of acid gelation increases with
increasing pH of the heat treatment (10,14) and
acid gels from milk preheated at higher pH
values also show higher gel strength.
• This suggests that either the presence of
denatured whey proteins and K-CN in the serum
or their absence from the micellar surface aid
the acid coagulation process of milk, leading to
a firmer gel.

28. • Since whey proteins have a higher isoelectric point
than the caseins, the first step in acid-induced
aggregation is the aggregation of the denatured
whey proteins, followed by aggregation of the
caseins with decreasing pH.
• The whey protein aggregates present in the serum have
better mobility than the whey protein-covered casein
micelles, making it easier for the small whey aggregates to
encounter and interact with one another, as well as with
the micelle-bound aggregates.

29. • The gel containing serum whey protein aggregates could
also hold more water than the gel containing casein
micelle-bound aggregates. In addition to pH of milk during
heating, these effects may also be achieved by selection of
optimal preheating time and temperature.
• If high levels of denatured whey protein and K-CN in the
serum are wanted, heating times in the order of 5-10 min at
85-95°C are required .

30. • UHT treatment can yield similar levels of whey protein
denaturation, but higher levels of micelle-associated
denatured whey protein and K-CN make this milk less
suitable for obtaining high gel strength with comparatively
little protein.
• However, should the opposite be required, i.e., high protein
products without excessively hard texture, then preheating
such as to minimize denatured whey protein and K-CN in
the serum phase of milk should be considered, e.g., by time-
temperature combinations or by milk properties.

31. Heat-stability
 High heat stability is another crucial feature of milk
proteins. Particularly concentrated milk systems can show
instability during intensive heat treatment, e.g., during in-
container sterilization.
 Heat coagulation of milk is promoted by dissociation of K-
CN from the micelles, but the association of whey proteins
with the casein micelles actually stabilizes the milk against
heat coagulation.

32. Schematic representation of the
effect of preheat treatment on
heat stability of high-heated
skim milk. (A – unheated skim
milk; B, C –skim milk preheated
at, e.g., 90°C for 45 s; D, E –
skim milk high-heated at, e.g.,
90°C for 30 min; B, D – pH 6.5;
C, E – pH 7.1).

33.  Hence, a controlled denaturation of whey proteins leading
to their association with the casein micelles, combined
with limited heat-induced dissociation of K-CN can be
used to increase the heat stability of milk.
 Because heat-induced dissociation of K-CN is more
extensive in concentrated milk than in unconcentrated
milk, preheating before evaporation for the manufacture of
evaporated milk or heat-stable milk powder is very
beneficial for high heat stability.

34.  Short heating times (<90 sec) at high temperature
(>100°C) are preferable over long heating times (>90
sec) at low temperature (<100°C)
 In addition, heating rates are important here; i.e., to
achieve maximum association of denatured whey
proteins with casein micelles and to avoid excessive
dissociation of K-CN, fast heating is beneficial.

35. CONCLUSIONS
 Casein-whey protein interactions occur on heat
treatment of milk. Their effects may be desired
(e.g., for yoghurt) or undesired (e.g., for cheese).
 In cases where these effects are undesired, choosing
heating conditions such that they are minimized is
important.
 However, in cases where casein-whey protein
interactions are desired, ample opportunity exists
to tailor them.

36.  By selecting heating time and temperature, but also
properties of the milk during heating, the interactions
between caseins and whey proteins can be directed such
that they either occur on the casein micelles or that they
occur in the milk serum.
 Thereby, the texture of yoghurt and the heat stability of
milk and milk protein ingredients can be optimized,
thereby further increasing the versatility of milk proteins
and their use throughout the dairy and non-dairy foods
industries.