1 Production and utilization of milk
1.1 Introduction
Milk is a fluid secreted by the female of all mamalian species, of which there
are more than 4000, for the primary function of meeting the complete
nutritional requirements of the neonate of the species. In addition, milk
serves several physiological functions for the neonate. Most of the non-
nutritional functions of milk are served by proteins and peptides which
include immunoglobulins, enzymes and enzyme inhibitors, binding or car-
rier proteins, growth factors and antibacterial agents. Because the nutri-
tional and physiological requirements of each species are more or less
unique, the composition of milk shows very marked inter-species differences.
Of the more than 4000 species of mammal, the milks of only about 180 have
been analysed and, of these, the data for only about 50 species are
considered to be reliable (sufficient number of samples, representative
sampling, adequate coverage of the lactation period). Not surprisingly, the
milks of the principal dairying species, i.e. cow, goat, sheep and buffalo, and
the human are among those that are well characterized. The gross compo-
sition of milks from selected species is summarized in Table 1.1; very
extensive data on the composition of bovine and human milk are contained
in Jensen (1995).
1.2 Composition and variability of milk
In addition to the principal constituents listed in Table 1.1, milk contains
several hundred minor constituents, many of which, e.g. vitamins, metal ions
and flavour compounds, have a major impact on the nutritional, technologi-
cal and sensoric properties of milk and dairy products. Many of these effects
will be discussed in subsequent chapters.
Milk is a very variable biological fluid. In addition to interspecies
differences (Table 1.1), the milk of any particular species varies with the
individuality of the animal, the breed (in the case of commercial dairying
species), health (mastitis and other diseases), nutritional status, stage of
lactation, age, interval between milkings, etc. In a bulked factory milk
supply, variability due to many of these factors is evened out, but some
variability will persist and will be quite large in situations where milk
2 DAIRY CHEMISTRY AND BIOCHEMISTRY
Table 1.1 Composition (%) of milks of some species
Species Total solids Fat Protein Lactose Ash
Human 12.2 3.8 1 .o 7.0 0.2
cow 12.7 3.7 3.4 4.8 0.7
Goat 12.3 4.5 2.9 4.1 0.8
Sheep 19.3 1.4 4.5 4.8 1.0
Pig
18.8 6.8 4.8 5.5 -
Horse 11.2 1.9 2.5 6.2 0.5
Donkey 11.7 1.4 2.0 7.4 0.5
Reindeer 33.1 16.9 11.5 2.8 -
Domestic rabbit 32.8 18.3 11.9 2.1 1.8
Bison 14.6 3.5 4.5 5.1 0.8
Indian elephant 31.9 11.6 4.9 4.1 0.7
Polar bear 47.6 33.1 10.9 0.3 1.4
Grey seal 67.7 53.1 11.2 0.7 -
production is seasonal. Not only do the concentrations of the principal and
minor constituents vary with the above factors, the actual chemistry of some
of the constituents also varies, e.g. the fatty acid profile is strongly influenced
by diet. Some of the variability in the composition and constituents of milk
can be adjusted or counteracted by processing technology but some differen-
ces may still persist. The variability of milk and the consequent problems
will become apparent in subsequent chapters.
From a physicochemical viewpoint, milk is a very complex fluid. The
constituents of milk occur in three phases. Quantitatively, most of the mass
of milk is a true solution of lactose, organic and inorganic salts, vitamins
and other small molecules in water. In this aqueous solution are dispersed
proteins, some at the molecular level (whey proteins), others as large
colloidal aggregates, ranging in diameter from 50 to 600nm (the caseins),
and lipids which exist in an emulsified state, as globules ranging in diameter
from 0.1 to 20 pm. Thus, colloidal chemistry is very important in the study
of milk, e.g. surface chemistry, light scattering and rheological properties.
Milk is a dynamic system owing to: the instability of many of its
structures, e.g., the milk fat globule membrane; changes in the solubility of
many constituents with temperature and pH, especially of the inorganic salts
but also of proteins; the presence of various enzymes which can modify
constituents through lipolysis, proteolysis or oxidation/reduction; the
growth of micro-organisms, which can cause major changes either directly
through their growth, e.g. changes in pH or redox potential (EJ or through
enzymes they excrete; and the interchange of gases with the atmosphere, e.g.
carbon dioxide. Milk was intended to be consumed directly from the
mammary gland and to be expressed from the gland at frequent intervals.
However, in dairying operations, milk is stored for various periods, ranging
from a few hours to several days, during which it is cooled (and perhaps
PRODUCTION AND UTILIZATION OF MILK 3
heated) and agitated to various degrees. These treatments will cause at least
some physical changes and permit some enzymatic and microbiological
changes which may alter the processing properties of milk. Again, it may be
possible to counteract some of these changes.
1.3 Classification of mammals
The essential characteristic distinguishing mammals from other animal
species is the ability of the female of the species to produce milk in
specialized organs (mammary glands) for the nutrition of its newborn.
1. Prototheria. This subclass contains only one order, Monotremes, the
species of which are egg-laying mammals, e.g. duck-billed platypus and
echidna, and are indigenous only to Australasia. They possess many
(perhaps 200) mammary glands grouped in two areas of the abdomen;
the glands do not terminate in a teat and the secretion (milk) is licked by
the young from the surface of the gland.
2. Marsupials. The young of marsupials are born live (viviparous) after a
short gestation and are ‘premature’ at birth to a greater or lesser degree,
depending on the species. After birth, the young are transferred to a
pouch where they reach maturity, e.g. kangaroo and wallaby. In marsu-
pials, the mammary glands, which vary in number, are located within the
pouch and terminate in a teat. The mother may nurse two offspring,
differing widely in age, simultaneously from different mammary glands
that secrete milk of very different composition, designed to meet the
different specific requirements of each offspring.
3. Eutherians. About 95% of all mammals belong to this subclass. The
developing embryo in utero receives nourishment via the placental blood
supply (they are referred to as placental mammals) and is born at a high,
but variable, species-related state of maturity. All eutherians secrete milk,
which, depending on the species, is more or less essential for the
development of the young; the young of some species are born sufficiently
mature to survive and develop without milk.
The number and location of mammary glands varies with species from
two, e.g. human, goat and sheep, to 14-16 for the pig. Each gland is
anatomically and physiologically separate and is emptied via a teat.
The wide interspecies variation in the composition (Table 1.1) and the
chemistry of the constituents of milk, as discussed elsewhere, renders milk
species-specific, i.e., designed to meet the requirements of the young of that
species. There is also a surprisingly good relationship between milk yield
and maternal body weight (Figure 1.1); species bred for commercial milk
production, e.g. dairy cow and goat, fall above the line.
The class Mammalia is divided into three subclasses:
4 DAIRY CHEMISTRY AND BIOCHEMISTRY
R,~, . . Oumea-Pig
Il.,lll*lcr . 1khidii:i
3
3 10.'
Body Wcight (kg)
Figure 1.1 Relation between daily milk yield and maternal body weight for some species
(modified from Linzell, 1972).
1.4 Structure and development of mammary tissue
The mammary glands of all species have the same basic structure and all
are located external to the body cavity (which greatly facilitates research on
milk biosynthesis). Milk constituents are synthesized in specialized epithelial
cells (secretory cells or mammocytes, Figure 1.2d) from molecules absorbed
from the blood. The secretory cells are grouped as a single layer around a
central space, the lumen, to form more or less spherical or pear-shaped
bodies, known as alveoli (Figure 1.2~). The milk is secreted from these calls
into the lumen of the alveoli. When the lumen is full, the rnyoepithelial cells
surrounding each alveolus contract under the influence of oxytocin and the
milk is drained via a system of arborizing ducts towards sinuses or cisterns
(Figure 1.2a) which are the main collecting points between suckling or
milking. The cisterns lead to the outside via the teat canal. Groups of alveoli,
which are drained by a common duct, constitute a lobule; neighbouring
lobules are separated by connective tissue (Figure 1.2b). The secretory
elements are termed the 'lobule-alveolar system' to distinguish them from
the duct system. The whole gland is shown in Figure 1.2a.
Milk constituents are synthesized from components obtained from the
blood; consequently, the mammary gland has a plentiful blood supply and
also an elaborate nervous system to regulate excretion.
PRODUCTION AND UTILIZATION OF MILK 5
WPI.LAR1ES
C0:NECTIbE
ISSUE
N LK PRVEIN
GOLGi
\ PPAHATUS
Figure 1.2 Milk-producing tissue of a cow, shown at progressively larger scale. (a) A
longitudinal section of one of the four quarters of a mammary gland; (b) arrangement of the
alveoli and the duct system that drains them; (c) single alveolus consisting of an elliptical
arrangement of lactating cells surrounding the lumen, which is linked to the duct system of the
mammary gland; (d) a lactating cell; part of the cell membrane becomes the membrane covering
fat droplets; dark circular bodies in the vacuoles of Golgi apparatus are protein particles, which
are discharged into the lumen. (From Patton, 1969.)
6 DAIRY CHEMISTRY AND BIOCHEMISTRY
3
t-”
10
0
0 100 200
Days
Figure 1.3 Time-course of mammary development in rats (from Tucker, 1969).
The substrates for milk synthesis enter the secretory cell across the basal
membrane (outside), are utilized, converted and interchanged as they pass
inwards through the cell and the finished milk constituents are excreted into
the lumen across the lumenal or apical membrane. Myoepithelial cells
(spindle shaped) form a ‘basket’ around each alveolus and are capable of
contracting on receiving an electrical, hormonally mediated, stimulus, there-
by causing ejection of milk from the lumen into the ducts.
Development of mammary tissue commences before birth, but at birth
the gland is still rudimentary. It remains rudimentary until puberty when
very significant growth occurs in some species; much less growth occurs in
other species, but in all species the mammary gland is fully developed at
puberty. In most species, the most rapid phase of mammary gland develop-
ment occurs at pregnancy and continues through pregnancy and partur-
ition, to reach peak milk production at weaning. The data in Figure 1.3
show the development pattern of the mammary gland in the rat, the species
that has been thoroughly studied in this regard.
Mammary development is under the regulation of a complex set of
hormones. Studies involving endocrinectomy (removal of different endocrine
organs) show that the principal hormones are oestrogen, progesterone,
growth hormone, prolactin and corticosteroids (Figure 1.4).
PRODUCTION AND UTILIZATION OF MILK 7
ATROPHIC GLAND
Ocst + GH + C
DUCT GROWTH
LOBULO-ALVEOLAR GROWTH
MILK SECRETION
Figure 1.4 The hormonal control of mammary development in rats. Oest, Oestrogen; Prog,
progesterone; GH, growth hormone; PL, prolactin; C, corticosteroids.
1.5 Ultrastructure of the secretory cell
The structure of the secretory cell is essentially similar to that of other
eukaryotic cells. In their normal state, the cells are roughly cubical, c. 10 pm
in cross-section. It is estimated that there are c. 5 x 10’’ cells in the udder
of the lactating cow. A diagrammatic representation of the cell is shown in
Figure 1.2d. It contains a large nucleus towards the base of the cell and is
surrounded by a cell membrane, the plasmalemma. The cytoplasm contains
the usual range of organelles:
0 mitochondria: principally involved in energy metabolism (tricarboxylic
acid (Krebs) cycle);
0 endoplasmic reticulum: located towards the base of the cell and to which
are attached ribosomes, giving it a rough appearance (hence the term,
rough endoplasmic reticulum, RER). Many of the biosynthetic reactions
of the cell occur in the RER;
0 Golgi apparatus: a smooth membrane system located toward the apical
region of the cell, where much of the assembly and ‘packaging’ of
synthesized material for excretion occur;
a DAIRY CHEMISTRY AND BIOCHEMISTRY
0 lysosomes: capsules of enzymes (usually hydrolytic) distributed fairly
uniformly throughout the cytoplasm.
Fat droplets and vesicles of material for excretion are usually apparent
toward the apical region of the cell. The apical membrane possesses
microvilli which serve to greatly increase its surface area.
1.6 Techniques used to study milk synthesis
1.6.1 Arteriovenous concentration diferences
The arterial and veinous systems supplying the mammary gland (Figure 1.5)
are readily accessible and may be easily cannulated to obtain blood samples
for analysis. Differences in composition between arterial and venous blood
give a measure of the constituents used in milk synthesis. The total amount
of constituent used may be determined if the blood flow rate is known,
which may be easily done by infusing a known volume of cold saline
Figure 1.5 The blood vessel and nerve supply in the mammary glands of a cow. Circulatory
system (arteries, white; veins, stippled): h, heart; a, abdominal aorta; pa, external pudic artery;
pv, external pudic vein; s, subcutaneous abdominal vein; c, carotid artery; j, jugular vein.
Nerves: 1, first lumbar nerve; 2, second lumbar nerve; 3, external spermatic nerve; 4, perineal
nerve. A and V show blood sampling points for arteriovenous (AV) difference determinations
(Mepham, 1987).
PRODUCTION AND UTILIZATION OF MILK 9
solution into a vein and measuring the temperature of blood a little further
downstream. The extent to which the blood temperature is reduced is
inversely proportional to blood flow rate.
1.6.2 Isotope studies
Injection of radioactively labelled substrates, e.g. glucose, into the blood-
stream permits assessment of the milk constituents into which that substrate
is incorporated. It may also be possible to study the intermediates through
which biosynthesis proceeds.
1.6.3 Perfusion of isolated gland
In many species, the entire gland is located such that it may be readily
excised intact and undamaged. An artificial blood supply may be connected
to cannulated veins and arteries (Figure 1.6); if desired, the blood supply
may be passed through an artificial kidney. The entire mammary gland may
thermometer
Figure 1.6 Diagram of circuit for perfusion of an isolated mammary gland of a guinea-pig., G,
mammary gland; A, artery; V, veins (from Mepham, 1987).
10 DAIRY CHEMISTRY AND BIOCHEMISTRY
be maintained active and secreting milk for several hours; substrates may
readily be added to the blood supply for study.
1.6.4 Tissue slices
The use of tissue slices is a standard technique in all aspects of metabolic
biochemistry. The tissue is cut into slices, sufficiently thin to allow adequate
rates of diffusion in and out of the tissue. The slices are submerged in
physiological saline to which substrates or other compounds may be added.
Changes in the composition of the slices and/or incubation medium give
some indication of metabolic activity, but extensive damage may be caused
to the cells on slicing; the system is so artificial that data obtained by the
tissue slice technique may not pertain to the physiological situation. How-
ever, the technique is widely used at least for introductory, exploratory
experiments.
1.6.5 Cell homogenates
Cell homogenates are an extension of the tissue slice technique, in which the
tissue is homogenized. As the tissue is completely disorganized, only
individual biosynthetic reactions may be studied in such systems; useful
preliminary work may be done with homogenates.
1.6.6 Tissue culture
Tissue cultures are useful for preliminary or specific work but are in-
complete.
In general, the specific constituents of milk are synthesized from small
molecules absorbed from the blood. These precursors are absorbed across
the basal membrane but very little is known about the mechanism by which
they are transported across the membrane. Since the membrane is rich in
lipids, and precursors are mostly polar with poor solubility in lipid, it is
unlikely that the precursors enter the cell by simple diffusion. It is likely, in
common with other tissues, that there are specialized carrier systems to
transport small molecules across the membrane; such carriers are probably
proteins.
The mammary gland of the mature lactating female of many species is by
far the most metabolically active organ of the body. For many small
mammals, the energy input required for the milk secreted in a single day
may exceed that required to develop a whole litter in utero. A cow at peak
lactation yielding 45 kg milk day-' secretes approximately 2 kg lactose and
1.5 kg each of fat and protein per day. This compares with the daily weight
gain for a beef animal of 1-1.5 kgday-', 60-70% of which is water. In large
PRODUCTION AND UTILIZATION OF MILK 11
measure, a high-yielding mammal is subservient to the needs of its mam-
mary gland to which it must supply not only the precursors for the synthesis
of milk constituents but also an adequate level of high-energy-yielding
substrates (ATP, UTP, etc.) required to drive the necessary synthetic
reactions. In addition, minor constituents (vitamins and minerals) must be
supplied.
1.7 Biosynthesis of milk constituents
The constituents of milk can be grouped into four general classes according
to their source:
0 organ-(mammary gland) and species-specific (e.g. most proteins and
0 organ- but not species-specific (lactose);
0 species- but not organ-specific (some proteins);
0 neither organ- nor species-specific (water, salts, vitamins).
The principal constituents (lactose, lipids and most proteins) of milk are
synthesized in the mammary gland from constituents absorbed from blood.
However, considerable modification of constituents occurs in the mammary
gland; the constituents are absorbed from blood through the basal mem-
brane, modified (if necessary) and synthesized into the finished molecule
(lactose, triglycerides, proteins) within the mammocyte (mainly in the
endoplasmic reticulum) and excreted from the mammocyte through the
apical membrane into the lumen of the alveolus.
We believe that it is best and most convenient to describe the synthesis
of the principal constituents in the appropriate chapter.
lipids);
1.8 Production and utilization of milk
Sheep and goats were domesticated early during the Agricultural Revo-
lution, 8000-10000 years ago. Cattle were domesticated later but have
become the principal dairying species in the most intense dairying areas,
although sheep and goats are very important in arid regions, especially
around the Mediterranean. Buffalo are important in some regions, especially
in India and Egypt. Mare’s milk is used extensively in central Asia and is
receiving attention in Europe for special dietary purposes since its compo-
sition is closer to that of human milk than is bovine milk.
Some milk and dairy products are consumed in probably all regions of
the world but they are major dietary items in Europe, North and South
America, Australia, New Zealand and some Middle Eastern countries. Total
milk production in 1996 was estimated to be 527 x lo6 tonnes, of which 130,
12 DAIRY CHEMISTRY AND BIOCHEMISTRY
Table 1.2 Consumption (kg caput-' annum-I) of liquid milk, 1993 (IDF, 1995)
Country Total Country Total
Russia" 252 Luxembourg" 86
Ireland" 182 Netherlands 84
Iceland 180 Hungary 81
Finland 170 Estonia" 81
Norway 147 Canada 77
Sweden 126 France 77
Denmark 115 Italy 75
United Kingdom 115 Germany 70
Spain 115 Greece" 67
Switzerland 101 Belgium 65
New Zealand 101 India 51
Australia 99 Lithuaniao 46
Czech and Slovak Reps" 97 Japan 42
USA 93 South Africa 38
Austria 92 Chile" 18
'Data for 1991, from IDF (1993).
Table 1.3 Consumption (kg caput-' annum-*) of cheese, 1993 (IDF, 1995)
Country Fresh Ripened Total
France
Greece"
Italy
Belgium
Germany
Lithuania"
Iceland
Switzerland
Sweden
Luxembourg"
Netherlands
Denmark
Finland
Norway
Canada
USA
Austria
Czech and Slovak Reps"
Estonia
Australia
United Kingdom
New Zealand
Hungary
Russia"
Spain
Ireland"
Chile"
South Africa
Japan
India
7.5
0.2
6.7
4.7
8.0
11.6
5.2
2.8
0.9
5.0
1.7
0.9
2.3
0.2
0.9
1.3
3.9
4.0
5.6
-
-
-
3.3
2.8
-
-
2.0
0.1
0.2
0.2
15.5
21.8
13.4
15.1
10.5
6.8
11.9
13.6
15.5
11.3
14.1
14.5
12.0
14.0
12.4
11.9
7.5
6.6
4.4
-
-
-
4.6
4.9
-
-
2.0
1.5
1.2
-
22.8
22.0
20.1
19.8
18.5
18.4
17.1
16.4
16.4
16.3
15.8
15.4
14.3
14.2
13.3
13.2
11.4
10.6
10.0
8.8
8.3
8.1
7.9
7.7
7.0
5.6
4.0
1.6
1.4
0.2
"Data for 1991, from IDF (1993).
PRODUCTION AND UTILIZATION OF MILK 13
Table 1.4 Consumption (kg caput-' annum-I) of butter, 1993
(IDF, 1995)
Country Butter
Lithuania"
New Zealand
Belgium
France
Germany
Russia"
Estonia
Luxembourg"
Finland
Switzerland
Czech and Slovak Reps"
Austria
Denmark
United Kingdom
Ireland"
Netherlands
Australia
Canada
Norway
Sweden
Iceland
USA
Italy
Greece"
India
Hungary
Japan
Chile"
South Africa
Spain
18.8
9.3
7.0
6.8
6.8
6.5
5.9
5.8
5.3
5.3
5.0
4.3
4.1
3.5
3.4
3.3
3.3
3.0
2.3
2.3
2.2
2.1
1.8
1.1
0.1
0.9
0.7
0.6
0.5
0.2
"Data for 1991, from IDF (1993).
103, 78, 26 x lo6 tonnes were produced in western Europe, eastern Europe,
North America and the Pacific region, respectively (IDF, 1996). The
European Union and some other countries operate milk production quotas
which are restricting growth in those areas. Data on the consumption of
milk and dairy products in countries that are members of the International
Dairy Federation (IDF) are summarized in Tables 1.2-1.6. Milk and dairy
products are quite important in several countries that are not included in
Tables 1.2-1.6 since they are not members of the IDF.
Because milk is perishable and its production was, traditionally, seasonal,
milk surplus to immediate requirements was converted to more stable
products, traditional examples being butter or ghee, fermented milk and
cheese; smaller amounts of dried milk products were produced traditionally
by sun-drying. These traditional products are still very important and
many new variants thereof have been introduced. In addition, several
new products have been developed during the past 130 years, e.g.
14 DAIRY CHEMISTRY AND BIOCHEMISTRY
Table 1.5 Consumption (kg caput-' annum-') of cream (but-
terfat equivalent), 1993 (IDF, 1995)
~
Country Total
Sweden
Denmark
Lithuania"
Luxembourg"
Iceland
Norway
Switzerland
Russia"
Finland
Germany
Estonia
Hungary
Belgium
Austria
New Zealand
United Kingdom"
Greece"
France
Czech and Slovak Reps"
Ireland"
Netherlands
Canada
USA
Spain
Italy
South Africa
Japan
Chile"
3.0
2.9
2.9
2.6
2.4
2.4
2.3
2.1
2.0
1.8
1.7
1.6
1.5
1.3
1.3
1.1
1 .o
1 .o
0.9
0.9
0.7
0.6
0.6
0.4
0.3
0.3
0.2
0.2
"Data for 1991, from IDF (1993).
sweetened condensed milk, sterilized concentrated milk, a range of milk
powders, UHT sterilized milk, ice-creams, infant foods and milk protein
products.
One of the important developments in dairy technology in recent years
has been the fractionation of milk into its principal constituents, e.g. lactose,
milk fat fractions and milk protein products (caseins, caseinates, whey
protein concentrates, whey protein isolates, mainly for use as functional
proteins but more recently as 'nutraceuticals', i.e. proteins for specific
physiological and/or nutritional functions, e.g. lactotransferrin, immuno-
globulins).
As a raw material, milk has many attractive features:
1. Milk was designed for animal nutrition and hence contains the necessary
nutrients in easily digestible forms (although the balance is designed for
PRODUCTION AND UTILIZATION OF MILK
Table 1.6 Consumption (kg caput-' annum-') of fermented
milks, 1993 (IDF, 1995)
Country Total
Finland 37.0
Sweden 28.6
Iceland 25.9
Netherlands 20.7
France 17.3
Switzerland 17.0
India 16.1
Denmark 15.1
Lithuania" 14.6
Germany 12.2
Austria 11.1
Spain 9.8
Belgium 9.6
Estonia 8.8
Czech and Slovak Reps" 8.8
Japan 8.5
Luxembourg" 7.0
Greece" 6.8
Norway 6.3
Italy 5.0
Australia 4.8
United Kingdom" 4.8
Chile" 4.1
Hungary 3.6
South Africa 3.6
Ireland" 3.3
Canada 3.0
USA 2.1
15
aData for 1991, from IDF (1993).
the young of a particular species) and free of toxins. No other single food,
except the whole carcass of an animal, including the bones, contains the
complete range of nutrients at adequate concentrations.
2. The principal constituents of milk, i.e. lipids, proteins and carbohydrates,
can be readily fractionated and purified by relatively simple methods, for
use as food ingredients.
3. Milk itself is readily converted into products with highly desirable
organoleptic and physical characteristics and its constituents have many
very desirable and some unique physicochemical (functional) properties.
4. The modern dairy cow is a very efficient convertor of plant material;
average national yields, e.g. in the USA and Israel, are about 8000 kg
annum- ', with individual cows producing up to 20000 kg annum-'. In
terms of kilograms of protein that can be produced per hectare, milk
16 DAIRY CHEMISTRY AND BIOCHEMISTRY
8 3
v;
x
d
Sclcc1cd I’nod products
Figure 1.7 Number of days of protein supply for a moderately active man produced per hectare
yielding selected food products.
production, especially by modern cows, is much more efficient than meat
production (Figure 1.7) but less efficient than some plants (e.g. cereals
and soybeans). However, the functional and nutritional properties of milk
proteins are superior to those of soy protein, and since cattle, and
especially sheep and goats, can thrive under farming conditions not
suitable for growing cereals or soybeans, dairy animals need not be
competitors with humans for use of land, although high-yielding dairy
cows are fed products that could be used for human foods. In any case,
dairy products improve the ‘quality of life’, which is a desirable objective
per se.
PRODUCTION AND UTILIZATION OF MILK 17
Table 1.7 Diversity of dairy products
~
Process
Primary product Further products
Centrifugal
separation
Concentration
thermal evaporation
or
ultrafiltration
Concentration
and
drying
coagulation
Enzymatic
Cream Butter, butter oil, ghee
Creams: various fat content
(HTST pasteurized or UHT sterilized),
coffee creams, wipping creams, dessert creams
Cream cheeses
Powders, casein, cheese, protein concentrates
In-container or UHT-sterilized
Skim milk
concentrated milks;
sweetened condensed milk
dietary products
Whole milk powders; infant formulae;
Cheese
Rennet casein
Whey
Acid coagulation Cheese
Acid casein
Whey
Fermentation
Freezing
Miscellaneous
1000 varieties; further products, e.g.
processed cheese, cheese sauces, cheese dips
Cheese analogues
Whey powders, demineralized whey powders,
whey protein concentrates, whey protein
isolates, individual whey proteins, whey
protein hydrolysates, neutraceuticals
Lactose and lactose derivatives
Fresh cheeses and cheese-based products
Functional applications, e.g. coffee creamers,
meat extenders; nutritional applications
Whey powders, demineralized whey powders,
whey protein concentrates, whey protein
isolates, individual whey proteins, whey
protein hydrolysates, neutraceuticals
Various fermented milk products, e.g.
yoghurt, buttermilk, acidophilus milk,
bioyoghurt
Ice-cream (numerous types and formulations)
Chocolate products
5. One of the limitations of milk as a raw material is its perishability - it is
an excellent source of nutrients for micro-organisms as well as for
humans. However, this perishability is readily overcome by a well-
organized, efficient dairy industry.
Milk is probably the most adaptable and flexible of all food materials, as
will be apparent from Table 1.7, which shows the principal families of
milk-based foods - some of these families contain several hundred different
products.
Many of the processes to which milk is subjected cause major changes in
the composition (Table 1.8), physical state, stability, nutritional and sensoric
18 DAIRY CHEMISTRY AND BIOCHEMISTRY
Table 1.8 Approximate composition (%) of some dairy products
Product Moisture Protein Fat Sugars" Ash
Light whipping cream 63.5 2.2 30.9 3.0 0.5
Butter 15.9 0.85 81.1 0.06 2.1
Anhydrous butter oil 0.2 0.3 99.5 0.0 0.0
Ice-creamb 60.8 3.6 10.8 23.8 1 .o
Evaporated whole milk 74.0 6.8 7.6 10.0 1.5
Sweetened condensed milk 27.1 7.9 8.7 54.4 1.8
Whole milk powder 2.5 26.3 26.7 38.4 6.1
Whey powder' 3.2 12.9 1.1 74.5 8.3
Casein powder 7.0 88.5 0.2 0.0 3.8
Cottage cheese, creamed 79.0 12.5 4.5 2.7 1.4
Qua%
72.0 18.0 8.0 3.0 -
Camembert cheese 51.8 19.8 24.3 0.5 3.7
Blue cheese 42.4 21.4 28.7 2.3 5.1
Cheddar cheese 36.7 24.9 33.1 1.3 3.9
Emmental cheese 36.0 28.9 30.0 - -
Parmesan cheese 29.2 35.7 24.8 3.2 6.0
Mozzarella cheese 54.1 19.4 31.2 2.2 2.6
Processed cheesed 39.2 22.1 31.2 1.6 5.8
Acid whey 93.9 0.6 0.2 4.2 -
"Total carbohydrate.
bHardened vanilla, 19% fat.
'Cheddar (sweet) whey.
dArnerican pasteurized processed cheese.
Skim milk powder 3.2 36.2 0.8 52.0 7.9
attributes of the product; some of these changes will be discussed in later
chapters.
1.9 Trade in milk products
Milk and dairy products have been traded for thousands of years and are
now major items of trade. According to Verheijen, Brockman and Zwanen-
berg (1994), world dairy exports were US23 x lo9 in 1992; the major flow
of milk equivalent is shown in Figure 1.8. Import and export data, as well
as much other interesting statistical data on the world dairy industry, are
provided by Verheijen, Brockman and Zwanenberg (1994), including a list
of the principal dairy companies in the world in 1992, the largest of which
was Nestle, which had a turnover from dairy products of US$10.6 x lo9 (c.
39% of total company turnover).
Traditionally, dairy products (cheese, fermented milks, butter) were
produced on an artisanal level, as is still the case in underdeveloped regions
and to some extent in highly developed dairying countries. Industrialization
commenced during the nineteenth century and dairy manufacturing is now
a well-organized industry. One of the features of the past few decades has
Figure 1.8 Trade flows greater than 250000tonnes in milk equivalents, 1992 (in 1000tonnes) (from Verheigen, Brockrnan and Zwaneberg, 1994).
20 DAIRY CHEMISTRY AND BIOCHEMISTRY
been the amalgamation of smaller dairy companies both within countries,
and, recently, internationally. Such developments have obvious advantages
in terms of efficiency and standardization of product quality but pose the
risk of over-standardization with the loss of variety. Greatest diversity
occurs with cheeses and, fortunately in this case, diversity is being preserved
and even extended.
References
IDF (1993) Consumption Statistics for Milk and Milk Products. Bulletin 282, International
IDF (1995) Consumption Statistics for Milk and Milk Products. Bulletin 301, International
IDF (1996) The World Dairy Situation, 1996. Bulletin 314, International Dairy Federation,
Jensen, R.G. (ed.) (1995) Handbook of Milk Composition, Academic Press, San Diego.
Linzell, J.L. (1972) Milk yield, energy loss, and mammary gland weight in different species.
Mepham, T.B. (1987) Physiology of Lactation, Open University Press, Milton Keynes, UK.
Patton, S. (1969) Milk. Sci. Am., 221, 58-68.
Tucker, H.A. (1969) Factors affecting mammary gland cell numbers. J. Dairy Sci., 52, 720-9.
Verheigen, J.A.G., Brockman, J.E. and Zwanenberg, A.C.M. (1994) The World Dairy Industry:
Dairy Federation, Brussels.
Dairy Federation, Brussels.
Brussels.
Dairy Sci. Abstr., 34, 351-60.
Deselopments and Strategy, Rabobank Nederland, Amsterdam.
Suggested reading
Cowie, A.T. and Tindal, J.S. (1972) The Physiology of Lactation, Edward Arnold, London.
Jensen, R.G. (ed.) (1995) Handbook of Milk Composition, Academic Press, San Diego.
Larson, B.L. and Smith, V.R. (1 974- 1979) Lactation: A Comprehensive Treatise, Academic
Mepham, T.B. (1975) The Secretion of Milk, Studies in Biology Series No. 60, Edward Arnold,
Mepham, T.B. (ed.) (1983) Biochemistry of Lactation, Elsevier, Amsterdam.
Mepham, T.B. (1987) Physiology of Lactation, Open University Press, Milton Keynes, UK.
Press, New York, Vols 1-4.
London.
