MILK PROTEINS

Milk Protein
 Milk proteins are among the most valuable protein as they contain all

the essential amino acids

 So, it is called a complete food from protein supplementation view

point
 Milk contains about 3.75- 4.25% protein: the principle proteins being

CASEIN, LACTALBUMIN and LACTOGLOBULIN (Whey protein)

 Of these, Casein constitutes 80% of the total and Lactoglobulin 18%;

Lactalbumin is present in very small amount (0.05- 0.1%)

 Casein is phospho-protein while lactalbumin and lactoglobulin is a

simple protein
Milk protein fractions
Casein

 Found only in milk

 Constitute about 80% of total protein
 First separated from milk in 1830, by adding acid to milk
 Is dispersed in milk in the form of micelles; Casein micelles are
spherical in shape and 0.04 to 0.3 µm in diameter
 Is easily separated from milk, either by acid precipitation or by
adding rennin but are resistant to heat denaturation
 But prolonged heating of fresh milk at 100- 120 C under pressure
causes precipitation of casein
Casein includes 5 different types denoted αs1-, αs2-, β-, κ- and γ- casein,
which differ in primary structure and properties.

Molecular weights of Casein

fractions:

αs1-casein (MW 23 KD),

αs2-casein (MW 25 KD),

β-casein (MW 24 KD),

κ-casein (MW 19 KD).

Milk protein (Casein)
 Casein are composed of the following amino acids:

Microbial protein
20.2% Glutamic Acid
Feed 10.2% Proline
8.3% Leucine*
7.4% Lysine*
6.5% Valine*
6.4% Aspartic Acid
5.7% Serine
5.7% Tyrosine
5.5% Isoleucine*
4.5% Phenylalanine*
4.4% Threonine*
3.7% Arginine
2.8% Histidine*
2.7% Alanine
2.5% Methionine*
2.4% Glycine
alpha-ca 1.1% Tryptophan*
sein 0.3% Cystine

The amino acids marked with an asterisk are called essential amino acids, because they cannot be synthesized in body,
and must be obtained from food directly. All essential amino acids are present in casein protein.

Casein is deficient in cystiene and cystine so give negative result with Sulphur test
 Normally occurs in Calcium- Caseinate- Phosphate complex in milk
 So, yields amino acids and phosphoric acid on hydrolysis as it
contains about 0.85% Phosphorous
 Casein occurs in three forms viz. ,  and . - casein is
responsible for the stabilization of micelle in milk

 - casein has two fractions: s and - casein. s –casein is also

called acid (H+) and Ca++ sensitive casein as it can be precipitated by

acid/Ca ion under certain condition while - casein is insensitive to
Ca ion and is the site for action of RENNIN
 - casein constitute about 75% of the total casein,  and - fraction
constitute 22% and 3% respectively
Whey protein
Milk  precipitation at pH 4.6  Supernatant (whey proteins )

 In 1895, the whey proteins were separated into globulin and albumin
fractions
 Whey proteins remain in solution when casein is coagulated by acid
or rennet
 Heat labile in nature so are easily heat denatured ( >650C)
 Globular proteins
 More water soluble than caseins
 Sulfur-containing amino acids (Cysteine and Cystine)
 Have good gelling and whipping properties
 55% ß-lactoglobulin, 25% α-lactalbumin and rest 20% is blood
serum albumin, immunoglobulins, lactoferrin, transferrin,
proteases/peptones, etc
 ß-lactoglobulin is a carrier of vitamin A but is absent in human milk

 α-Lactalbumin plays a critical role in the synthesis of lactose in the

mammary gland

 Immunoglobulins play a role in the animal's immune system

 Lactoferrin and transferrin play an important role in iron absorption

The process of milk secretion in the udder of a cow (partially adapted from
Wattiaux, 1996). Milk is secreted in the alveoli system of the mammary
gland. Several substances can pass the cell membrane from the blood stream
(water, minerals, vitamins, immune-globulins), whilst others need
transporters and are produced in the secretory cells (proteins, fat, lactose).
 Whey is the largest by-product of the dairy industry both in terms of volume
and milk solids as it contains 50% of original milk solids including whey
protein lactose, minerals, water soluble vitamins and residual lipids.
 It is estimated that during the production of 1 Kg cheese, approximately 9 Kg of
whey are produced.
 Functional properties of whey proteins, such as emulsifying, water/fat holding,
foaming, thickening and gelling properties, also make them interesting to be used as
a food ingredient.
VARITIES OF WHEY
Acid whey, with a pH less than or equal to 5.1, is produced during the manufacture of
cottage cheese, ricotta and cream cheeses and has applications in such products as salad
dressings and snack.
Sweet whey, with a pH of 5.5 or greater, is created during the manufacture of rennet-
coagulated cheese.
Whey protein concentrate (WPC) is produced by concentrating, using filtration, the
protein components of pasteurized whey. WPC typically contains 34% or more protein.
Whey protein isolate (WPI), is manufactured in a manner similar to WPC, but with a
resulting concentration of 90% or more protein.
Reduced-lactose whey, has a lactose content of less than 60%; the lactose is removed
through filtration, dialysis or precipitation.
Demineralized whey, may be created by drying whey that already has been processed to
remove a portion of its mineral content via precipitation, ion exchange, electrodialysis or
membrane filtration. Reduced-mineral whey cannot contain more than 7% ash.
 Deterioration of Milk Protein

 Two amino acids in milk, methionine and cystine are sensitive to light

and may be degraded on exposure to light (off-flavor )

 The predominant cause of protein degradation is through enzymes

called proteases

 Airborne bacterial contamination is the main reason

 Influence of Heat Treatment on Milk Proteins

 Caseins are stable to heat treatment (HTST no effect) but

Whey proteins are more sensitive to heat than the caseins
 Denaturation causes a change in the physical structure of
proteins
 When milk is heated to 80 C or above Sulphyhydryl Breakdown of
Disulphide bond
group (-SH) get liberated which shows reducing
properties and characteristics Caramel or Cooked flavor Sulphur release
 Denaturation of β-lactoglobulin causes the cooked flavor bad smell
of heated (above 75°C)milk
Chemical properties of Casein

1. Amphoteric properties-
Casein +HCL Casein hydrochloride < 4.6

R1.NH2 + HCL R1.NH2.HCL

 Casein +NAOH Sodium Caseinate > 4.6

R2. COOH +NAOH R2C00NA + H20

2. Hydrolysis: Casein yields a mixture of α amino acids and
phosphoric acids on hydrolysis with acids, bases and enzymes.
3. Coagulation: Casein is coagulated by acids, rennet, alcohol, heavy
salts (Mercuric chloride), NaCl, MgSO4 and heat (1310c-1380C)

Coagulation of milk is mainly due to its casein and albumin content.

It is not coagulated easily in fresh milk having low acidity by heat
until heated to a high temperature ((1310C-1380C)
However, Casein is coagulated in low temperature when milk
contains high amount of acidity
Use of Casein

 Casein is used in plastic production like rims of eye glasses, pen

barrel, umbrella handle, buttons, comb, etc.
 For glue production
 Use in textile production
 Use in leather industry
 Paper coating
 Use for medicine
 Edible casein use for infant’s food, ice- cream, coffee whitener
Nutritive value of Milk protein

 Milk protein principally casein and lactoalbumin are complete

protein. They contain all essential amino acids
 Lactoalbumin is source of two essential amino acids Lysine and
tryptophan
 Good source of animal protein for vegetarian

 Digestibility of milk protein is higher. 97-98% of milk protein gets

digested and 76% get absorbed in body
 Casein is good source of calcium and phosphorous for bone and teeth
 Proteins are essential constituents of living cells
Lactose

 Exists only in milk in true solution form in milk serum

 The average lactose content of milk varies between 4.7 and 4.9%

 Lactose is a source of energy for the young calf and provides 4

calories/g
 It is less soluble in water and is less sweet than sucrose

 It can be broken down to Glucose and Galactose by bacteria that have

the enzyme b-lactosidase
 The glucose and galactose can then be fermented to lactic acid; milk
goes sour
 Fermentation also give a desired flavor
Chemical properties of Milk lactose
1. Caramelization: When milk is heated 1000c-1300c, α lactose monohydrate
loose its crystalline water and changed into anhydrous form
Prolong heating milk turns to light brown or caramel color due to production
of sulphydryl compound, giving COOKED smell

2. Reducing properties:
 Lactose is reducing sugar and reduces Fehling’s solution into cuprous oxide
C11H21010CHO + 2CU(OH) C11H21O10COOH+2H20+CU2O
(Cuprous oxide)
 Lactose reduces ammonical silver nitrate into silver mirror
C11H21010CHO +2AgNO 3 + 2NH4OH C11H21O10COOH +2Ag +H2O +
2NH4NO3
Lactobionic acid (Silver Mirror)
 Aq. solution of lactose reduces mercuric chloride into mercury

C11H21010CHO + HgCl2 +H2O C11H21O10COOH + Hg

+2HCL

3. Oxidation: Oxidizing agent like bromine, Iodine, etc. oxidizes lactose

into lactobionic acid

C11H21010CHO + 0 Oxidising agent C11H21O10COOH (Lactobionic acid)

4. Hydrolysis: on hydrolysis, splits into d glucose and d galactose
C12 H22 O11 +H2O Hydrolysis C6H12O6 + C6H12O6
Lactose D glucose D Galactose

5. Lactic fermentation : Lactic fermentation completes in two steps

i. C12 H22 O11 +H2O Hydrolysis

C6H12O6 + C6H12O6
Lactose

ii. 2C6H12O6 Lactic fermentation 4 CH3CHOHCOOH

Lactococcus lactis Lactic acids
Lactose Intolerance

 The inability of adults and children to digest lactose due to absence or

low production of lactase in intestine is called Lactose intolerance.
 Lactase deficiency or hypolactasia: Individuals have congenital
alactasia, a total absence of lactase caused by a genetic defect
 Lactase catalyzes the hydrolysis of lactose into Glucose and Galactose

 Susceptible people are unable to metabolize lactose and suffer from an

allergy; Diarrhea, vomiting, Allergies, stomach pain, abdominal
bloating, etc. are the major complains
 Most of the lactase enzyme production cease after weaning in
animal
Nutritional effects of CLD

 Congenital lactase deficiency (CLD), where the production of

lactase is inhibited from birth,

 Before the 20th century, babies born with CLD often did not survive

x- Soybean-derived infant formulas and manufactured lactose-free

dairy products
Milk Allergies

A milk allergy is an immune reaction to one of the many proteins in

animal milk, although it is most often caused by αS1-casein protein
in cow milk
Common manifestations are:
 Abdominal cramps
 Loose stool (which may contain blood or mucus)
 Diarrhea
 Vomiting
 Intermittent coughing
 Running nose or sinus infection
 Failure to thrive (slow to gain weight or height)
Milk enzyme, Pigments, gases and NPN

Enzymes
Catalyst

Lipase, protease,
lactase, amylase,
Enhancer Peroxidase,
Enzyme Oxidase,
phosphatase, etc.

Specific in
action

Inactive by
temperature
Enzymes in Milk
Enzymes Substrate Product

Protease protein Proteoses, Peptides, Amino

acids

lipase Fat Fatty acids and glycerols

Phosphatase Organic phosphate Free phosphate

Catalase Hydrogen peroxise H2O and 02

Amylase Starch Sugars

Lactase lactose Glucose and galactose

Function of enzymes in Milk

1. Protease:
 Casein hydrolyzing enzymes
 Plays important role in cheese ripening
 Protease in combination with lipase reduce 50% time on ripening
of cheese
 Provide good flavor in milk
 After completion of ripening convert casein into peptide and
amino acids
2.Lipase

 Fat splitting enzyme

 Liberate fatty acids

Tributyrin Lipase Butyric acid and Glycerol

Destroyed Bitter test or rancid flavor

in
pasteuriza
tion
3.Phosphatase

 Present in raw milk

 Inactivated by efficient pasteurization (61.1 0c 30 minutes 71.0c for
15 s)
 Presences indicates inadequate heating or contamination
 It can be determined by Phosphatase test
 2 types: Acid Phosphatase (4.2 pH), Alkaline Phosphatase (9.4 pH)
4. Catalase

 Present in very small amount in milk

 High leucocytes in milk increase Catalase activity
 High Somatic cell due to mastitis or udder infection

 Oxidising enzyme splits H202 into water and 02

 Catalase inactivated in 660c-700c during pasteurization

5. Amylase

 Starch splitting enzyme

 Split starch into sugar
 2 form : α amylase : Dextrin

β amylase: Maltose
 Amylase is low in infected milk
6.Reductase

 Reduces or decolorizes Methylene blue or oxidation reduction dyes

 Indicates the microbial contamination status of milk
 Higher the dye reduction time finer is the milk quality

Fresh milk

Methyl blue color

Color less (good quality milk)

7. Peroxidase

 Oxidising enzyme, act on peroxides and liberate 0 2

 Peroxidase content higher in infected milk

Lactic Acid

8. Lactase
 Hydrolysis of lactose producing glucose and galactose
Carbonic anhydrase

 Catalyse the hydrogenation of CO2 into Carbonic acid

C02 + H20 H2Co3

Carbonic anhydrase
Minor constituents
Absence or less in
1. Pigments human, goat, buffalo
milk

Yellow color of milk,

cream, butter, ghee
Carotene

Fat
soluble
Xanthophyll

Local,
Jersey, yak
Yellowish
red color of
corn
Yellow color of milk depends on the carotene/pigments received by
cow from feed.
Available in Berseem and green grasses.

Water
soluble

Riboflavin
Water
soluble
Greenish/
bluish color
in whey
Gases in Milk

 Some dissolved gases present in fresh milk C0 2, N2, 02

 N2, 02 from atmosphere and C02 from udder

 Some bacteria also produce gases in milk

Non protein nitrogenous compounds and Vitamins

 Urea, Uric acids, amine, Creatine, Creatinine, Xanthane, etc.

Vitamins
 Fat Soluble Vitamins: Vitamins A, D, E and K
 Water Soluble Vitamins:Vitamin C, B1, B2, B6, B12, pantothenic
acid, niacin, biotin, and folic acid
Minerals: Calcium, Magnesium, phosphorous, Potassium, Na, etc.