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Composition of Milk

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					Dairy Technology                                                      Composition of milk




Composition of Milk                            colostrum free, and containing the
                                               minimum prescribed percentages of
Definition of Milk                             milk fat and milk solids-not-fat.

Milk may be defined as the whole,              Milk constituents: the major
fresh, clean, lacteal secretion                constituents of milk are, water, fat,
obtained by the complete milking of            protein, lactose, ash or mineral
one or more healthy milch animals,             mater. The minor constituents are:
excluding that obtained within 15              phospholipids, sterols, vitamins,
days before or 5 days after calving or         enzymes, pigments, etc. the “true”
such periods as may be necessary               constituents are milk fat, casein and
to render the mil practically                  lactose.

Chemical composition of milk of different species.

   Name of               Water       Fat     Protein      Lactose        Ash
   species
Ass                          90.0     1.3       1.7          6.5          0.5
Buffalo                      84.2     6.6       3.9          5.2          0.8
Camel                        86.5     3.1       4.0          5.6          0.8
Cat                          84.6     3.8       9.1          4.9          0.6
Cow (foreign)                86.6     4.6       3.5          4.9          0.7
Dog                          75.4     9.6      11.2          3.1          0.7
Elephant                     67.8    19.6       3.1          8.8          0.7
Ewe                          79.4     8.6       6.7          4.3          1.0
Goat                         86.5     4.5       3.5          4.7          0.8
Guinea pig                   82.2     5.5       8.5          2.9          0.9
Human                        87.8     3.6       1.8          6.8          0.1
Llama                        86.5     3.2       3.9          5.6          0.8
Mare                         89.1     1.6       2.7          6.1          0.5
Reindeer                     68.2    17.1      10.4          2.3          1.5
Sow                          89.6     4.8       1.3          3.4          0.9
Whale                        90.1    19.6       9.5           -           1.0

Chemical composition of milk of foreign breeds of cow

Breeds                                   Percentage Composition
                      Water         Fat       Protein   Lactose        Ash
Holstein              87.74         3.4       3.22      4.87           0.68
Shorthorn             87.19         3.94      3.32      4.99           0.70
Ashyre                87.10         4.00      3.58      4.67           0.68
Brown Swiss           86.59         4.01      3.61      5.04           0.73
Guernsey              85.39         4.95      3.91      4.93           0.74
Jersey                85.09         5.37      3.92      4.93           0.71




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Dairy Technology                                                     Composition of milk



Food and Nutritive Value of Milk               products. Besides serving as a
Milk is almost an ideal food. It has           rich source of energy, fat
high nutritive value, It supplies body-        contains significant amounts of
building     proteins,    bone-forming         so-called essential fatty acids
minerals and health-giving vitamins            (lenoleic and arachi8donic). The
and furnishes energy-giving lactose            most distinctive role which milk
and milk fat. Besides supplying                fat plays in dairy products
certain essential fatty acids, it              concerns flavour of milk lipids is
contains the above nutrients in an             not duplicated by any other type
easily digestible and assimilable              of fat. Milk fat imparts a soft body,
form. All these properties make milk           smooth texture and rich taste to
an important food for pregnant                 dairy products. Lastly, milk lipids
mothers,        growing        children,       undoubtedly         enhance       the
adolescents,       adults,      invalids,      consumer acceptability of foods;
convalescents and patients alike.              they also serve the best interests
                                               of human nutrition through the
a. Protein:    Milk   proteins    are          incentive of eating what tastes
   complete proteins of high quality,          good.
   i.e. they contain all the essential
   amino-acids      in fairly large         e. Lactose: The principal functions
   amounts.                                    of lactose (carbohydrate) are to
                                               supply energy. However, lactose
b. Minerals: practically all the               also helps to establish a mildly
   mineral elements found in milk              acidic reaction in the intestine
   are essential for nutrition. Milk is        (which checks the growth of
   an excellent source of calcium              proteolytic      bacteria)   and
   and phosphorus, both of which,              facilitates assimilation.
   together with vitamin D, are
   essential for bone formation. Milk       f. Energy value: the energy-giving
   is rather low in iron, copper and           milk constituents and their
   iodine.                                     individual contributions are as
                                               follows:
c. Vitamins: these are accessory
   food factors which are essential            Milk fat          9.3 C/g
   for normal growth, health and the           Milk protein      4.1 C/g
   reproduction of living organisms.           Milk sugar        4.1 C/g
   Milk is a good source of vitamin a
   (provided the cow is fed                    Where 1 C (Food calorie) =
   suffici9ent green feed and fodder),         1000c (small calorie)
   thiamine, riboflavin, etc. However,         Note: the energy value of milk will
   milk is deficient in vitamin C.             vary with its composition. On
                                               average, cow milk furnishes 75
d. Fat: Milk fat (lipid) plays a               C/100 g and buffalo milk 100
   significant role in the nutritive           C/100 g
   value, flavour and physical
   properties of milk and milk



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Dairy Technology                                                    Composition of milk



G         Effect of processing             fat globules form coalescing and
                                           separating from on another. The
i.        Pasteurizing carried out with    emulsion may however, be broken
          reasonable care has no effect    by agitation (at low temperatures),
          on vitamin A, carotene,          heating, freezing, etc. when milk is
          riboflavin and a number of       held undisturbed, the fat globules
          remaining vitamins B, and        tend to rise to the surface to form a
          vitamin D. Of the remainder, a   cream layer. The thickest cream
          10% loss of ascorbic acid may    layer is secured from milk, which has
          be expected.                     higher fat content and relatively large
                                           fat globules (such as buffalo’s milk
ii.       Sterilization increases the      when compared with cow’s milk).
          losses of thiamine and           Chemically, milk fat is composed of
          ascorbic acid to 30 – 40% and    number of glyceride-esters of fatty
          50% respectively, though the     acids; on hydrolysis, milk fat
          remaining vitamins are but       furnished a mixture of fatty acids and
          little affected.                 glycerol. The fatty acids are
                                           saturated or unsaturated. Saturated
                                           fatty acids are relatively stable. On
      Physico-Chemical properties of       the other hand, the unsaturated ones
            Milk constituents              play an important role in the physico-
                                           chemical properties of milk fat.
A.        Major Milk Constituents
                                           c.     Milk proteins
a.      Water                              Proteins are among the most
Constitutes the medium in which the        complex of organic substances.
other milk constituents are either         They are vital for living organisms as
dissolved or suspended. Most of it is      they constitute an indispensable part
“free” and only a very small portion in    of the individual body cell. Proteins
the “bound” form, being firmly bound       are composed of a large number of
by milk proteins, phospholipids, etc.      amino-acids, some “essential” and
                                           others “non-essential”. The essential
b.      Milk fat (lipid)                   amino-acids are necessary in the
The bulk of the fat in milk exists in      diet for the formation of body
the form of small globules, which          proteins. On hydrolysis, proteins
average approximately 2 – 5 microns        furnish a mixture of amino-acids. The
in size (range 0.1 to 20 microns).         proteins of milk consist mainly of
This is an oil-in-water type emulsion.     casein, β-lactoglobulin, ά-lactalbumin,
The surface of these fat globules is       etc. casein exists only in milk and is
coated with an adsorbed layer of           found in the form of a calcium
material commonly known as the fat         caseinate-phosphate complex. It is
globule membrane, this membrane            present in the colloidal state. It forms
contains phospholipids and proteins        more than 8% of the total protein in
in the form of a complex, and              milk It may be precipitated by acid,
stabilizes the fat emulsion. In other      rennet,     alcohol,      heat       and
words, the membrane prevents the           concentration. Casein itself is



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Dairy Technology                                                    Composition of milk



composed of ά, β and γ fractions.          e.     Mineral matter of ash.
The heterogeneous nature of ά-
casein can be observed through             The mineral matter or salts of milk,
electrophoresis.                           although present in small quantities,
ά-casein is the component in casein        exert considerable influence on the
micelle that is responsible for the        physicochemical       properties     and
stabilization of the micelle in milk.      nutritive value of milk. The major salt
Later studies have also revealed that      constituents, i.e. those present in
ά-casein is composed of at least two       appreciable       amounts,       include
sub-fraction,       viz.      άs-casein    potassium, sodium, magnesium,
precipitable by calcium-ion under          calcium, phosphate, citrate, chloride,
certain conditions and also called         sulphate and bicarbonate; the trace
“calcium-sensitive casein”, and K-         elements include all other minerals
casein,     also     called    “calcium    and salt compounds. The mineral
insensitive casein”, not precipitable      salts of milk are usually determined
by calcium-ion. K-casein is the            after ashing. Although milk is acidic,
richest repository of carbohydrates        ash is distinctly basic. Part of the
as against other casein fractions. It is   mineral salts occurs in true solution
also the site for rennin actions.          while a part in the colloidal state.
β-lactoglobulin and ά-lactalbumin are
also known as whey or serum-               B.     Minor Milk constituents
proteins. They are also present in
the colloidal state and are easily         a.      Phospholipids
coaguable by heat.                         In milk, there are three types of
                                           phospholipids, viz. lecithin, cephalin
d.       Milk sugar or lactose.            and sphingomylin. Lecithin, which
                                           forms an important constituent of the
This exists only in milk. It is in true    fat globule membrane, contributes to
solution in the milk serum. On             the “richness” of flavour of milk and
crystallization from water, it forms       other dairy products. It is highly
hard gritty crystals. It is one-sixth as   sensitive to oxidative changes, giving
sweet as sucrose. Lactose is               rise to oxidized/metallic flavours.
responsible, under certain conditions,     Phospholipids        are      excellent
for the defect known as “sandiness”        emulsifying agents and no doubt
in ice cream or sweetened                  serve to stabilize the milk fat
condensed milk. Chemically, lactose        emulsion.
is composed of one molecule each
of glucose and galactose. Lactose          b.     Cholesterol
occurs in two forms, ά and β, both of      This appears to be present in true
which occur either as the hydrate or       solution in the fat, as part of the fat
the anhydrite. It is fermented by          globule membrane complex and in
bacteria to yield lactic acid and other    complex formation with protein in the
organic acids and is important both        non-fat-portion if milk.
in the production of cultured milk
products and in spoilage of milk and
milk products by souring.



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Dairy Technology                                                     Composition of milk



c.       Pigments                          (iii)   Phosphatase – capable of
                                                   splitting certain phosphoric
These are (i) fat soluble, such as                 acid     esters     (basis  of
carotene and xanthophylls, and (ii)                phosphatase test for checking
water soluble such as riboflavin.                  pasteurization efficiency)
Carotene is the colouring (the pure
substance of which has a reddish-          (iv)    Protease – protein splitting;
brown colour) is fat soluble and
responsible for the yellow colour of       (v)     Peroxidase and         Catalase
milk, cream, butter, ghee and other                decomposes             hydrogen
fat-rich dairy products. Besides                   peroxide.
contributing to the colour of cow milk,
carotene acts as a precursor of            e.      Vitamins
vitamin A. One molecule of β-              Although present in foods in very
carotene yields two molecules of           minute quantities, these are vital for
vitamin a while ά-carotene yields          the health and growth of living
only one.                                  organisms. As of today, over 25
Dairy animals differ in their capacity     vitamins have been reported. Those
to transfer carotene from feeds to         found in milk are: fat-soluble vitamins
milk fat; this varies with species,        A, D, E and K’ and water-soluble of
breed and individuality. Hence,            the “B-complex” group (such as
buffalo milk is white in colour. (The      thiamin or B1,, pantothenic acid,
carotinoid content of buffalo milk         niacin, pyridoxine or B6, biotin, B12,
varies from 0.25 to 0.48 µg/g, while       folic acid, etc) and vitamin C.
that of cow milk may be as high as         absence of vitamins in the diet over
30 µg/g)                                   prolonged        periods        causes
                                           “deficiency diseases”.
d.      Enzymes
These are “biological catalysts”           Physico-Chemical Properties of
which can hasten or retard chemical        Milk
changes       without      themselves
participating in the reactions. The        a.      acidity
enzymes are protein-like, specific in      Freshly drawn milk is amphoteric to
their actions and inactivated by heat;     litmus that is it turns red litmus blue
each      enzyme     has     its  own      and blue litmus red. However, it
inactivation    temperature.      The      shows certain acidity as determined
important milk enzymes are as              by titration with an alkali (sodium
follows:                                   hydroxide) in the presence of an
                                           indicator (phenolphthalein). This
(i)      Analase (diastase) – starch       acidity is also called Titrable acidity
         splitting                         (T.A) as it is determined by titration,
                                           is known as “natural” or “apparent”
(ii)     Lipase – fat splitting, leading   acidity and is caused by the
         to rancid flavour;                presence of casein, acid-phosphates,
                                           citrates, etc. in milk. The natural
                                           acidity of individual milk varies



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Dairy Technology                                                    Composition of milk



considerable       depending       upon    substance (when referred to water at
species, breed, individuality, stage of    40 C) is numerically equal to the
lactation, physiological condition of      density of that substance in metric
the udder, etc. but the natural acidity    system. The specific gravity of milk is
of fresh her milk is much more             usually expressed at 60 0F (15.6 0C).
uniform. The higher the solids-not-fat     The density or the specific gravity of
content in milk, the higher the natural    milk may be determined by either
acidity (N.A) and vice versa. The          determining the weight of a know
titrable acidity of cow milk varies on     volume or the volume of a known
an average from 0.13 to 0.14 percent       weight. The weight of a known
and buffalo milk from 0.14 to 0.15         volume may be determined either
per cent. “Developed” or “real”            with a pycnometer or with a
acidity is due to lactic acid, formed      hydrostatic balance; while the
as a result of bacterial action on         volume of a known weight is
lactose in the milk. Hence the titrable    determined by using lactometers, the
acidity of stored is equal to the sum      scale of which is calibrated not in
of natural acidity and developed           terms of volume but as a function of
acidity. The titrable acidity is usually   either density or specific gravity. The
expressed as “percentage of lactic         common types of lactometers are
acid.                                      Zeal, Quevenne, etc.
                                           Milk is heavier than water. The
b.      pH                                 average specific gravity ranges (at
The pH of normal, fresh, sweet milk        600F) from 1.028 to 1.030 for cow
usually varies from 6.4 to 6.6 for cow     milk and 1.030 to 1.032 for buffalo
milk and 6.7 to 6.8 for buffalo milk.      milk and 1.035 to 1.037 for skim milk.
Higher pH values for fresh milk            The specific gravity of milk is
indicate udder infection (mastitis)        influenced by the proportion of its
and lower values, bacterial action.        constituents (i.e. composition), each
Note: The acidity and pH of fresh          of which has different specific gravity
milk vary with (i) species, (ii) breed,    approximately as follows: water –
(iii) individuality, (iv) stage of         1.000, fat – 0.93, protein – 1.346,
lactation and (v) health of the animal,    lactose – 1.666 and salts – 4.12
etc.                                       (solids-not-fat - 1.616).
                                           As milk fat is the lightest constituent,
B.       Density and Specific Gravity      the more there is of it the lower the
                                           specific gravity with be and vice
Whereas density of a substance is          versa. However, although buffalo
its mass (weight) per unit volume,         milk contains more fat than cow milk,
specific gravity is the ration of          its specific gravity is higher than the
density of the substance to density of     latter’s; this is because buffalo milk
a standard substance (water). Since        contains more solids-not-fat as well,
the density of a substance varies          which ultimately results in a higher
with temperature, it is necessary to       specific gravity.
specify the temperature when               The specific gravity of milk is
reporting densities or specific            lowered by addition of water and
gravities. The specific gravity of a       cream and increased by addition of



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Dairy Technology                                                   Composition of milk



skim milk or removal of fat. The          and protein contents of milk have no
percentage of total solids or solids-     direct effect on the freezing point of
not-fat in milk is calculated by using    milk. The drawbacks of the freezing
the following formula:\                   point test are; (i) it does not detect
                                          the addition of skim milk or removal
%TS = 0.25D +0.72                         of fat from the milk sample and (ii)
%SNF = 0.25D + 0.22F + 0.72               watered       milk,     which     has
Where        D = 1000 (d – 1)             subsequently soured, may pass the
D = density of sample of milk at 20       test.
0
 C (680F)
Note: the specific gravity of milk        D.     Colour of Milk
should not be determined for at least     The colour is a blend of the
one hour after it is drawn from the       individual effects produced by: (i) the
animals; else a lower-than-normal         colloidal casein particles and the
value will be obtained (due to the        dispersed fat globules, both of which
Recknagel phenomenon).                    scatter light and (ii) the carotene (to
                                          some extent xanthophylls) which
C.      Freezing Point of Milk            imparts a yellowish tint. Milk ranges
Milk freezes at temperature slightly      in colour from yellowish creamy
lower than water due t the presence       white (cow milk) to creamy white
of soluble constituents such as           (buffalo milk). The intensity of the
lactose, soluble salts, etc., which       yellow colour of cow milk depends
lower or depress the freezing point.      on various factors such as breed,
The       average    freezing     point   feeds, size of fat globules, fat
depression of cow milk is 0.547 0C        percentage of milk, etc. Certain
(31.02 0F) and buffalo milk 0.549 0C      breeds of cow impart a deeper
(31.01 0F); a freezing point              yellow tint to their milk than others.
depression lower than this value          The greater the intake of green feed,
indicates added water. Mastitis milk      the deeper yellow the colour of cow
shows a normal freezing point. The        milk. The larger the fat globules and
freezing point test of milk is a highly   the higher the fat percentage, the
sensitive one and even up to 3% or        greater the intensity of the yellow
watering can be detected.                 colour. Skim milk has a bluish, and
While the freezing point of normal        whey a greenish yellow colour
fresh milk is remarkably constant         (which in milk is masked by the other
and employed mainly for detection of      constituents present.
adulteration of milk with water,
souring results in a lowering of the      E.     Flavour
freezing point due to increase in the     This is composed of smell (odour)
amount of soluble molecules. Hence        and taste. The flavour of milk is
the freezing point should be              blend of the sweet taste or lactose
determined on unsoured samples for        and salty taste of minerals, both of
greatest accuracy. Boiling and            which are damped down by proteins.
sterilization increase the value of       The phospholipids, fatty acids and
freezing point depression, but            fat of milk also contribute to the
pasteurization has no effect. The fat     flavour.



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Dairy Technology                                                    Composition of milk



Changes in the flavour of milk occur       products,     the     spherical    and
due to type of feed, season, stage of      cylindrical forms are predominant.
lactation,     condition    of   udder,    Most bacteria vary from 1 to 5
sanitation     during    milking    and    microns in size. Although individual
subsequent handling of milk during         bacterial cells are invisible to the
storage. The sulfydryl compounds           naked eye, they form bacterial
significantly contribute to the cooked     colonies (consisting of large number
flavour of heated milk.                    of individual cells) which are visible.
Note: A pronounced flavour of any          Bacteria      are     found     nearly
kind is considered abnormal to milk.       everywhere in nature. They are
The source of abnormal flavours            found in large numbers in the soil,
may be due to: (i) bacterial growth;       sewage, decaying plants or animals,
(ii) feed; (iii) absorbed odour; (iv)      and are also present in air, water, etc.
chemical composition; (v) processing       Under       favourable      conditions,
and handling; (vi) chemical changes        bacteria multiply very rapidly and
and (vii) addition of foreign materials.   may double their number in 15
                                           minutes or less. Some bacteria also
MICROBIOLOGY OF MILK                       form ”spores”, which are tough
                                           resistant bodies within the bacterial
A.       Introduction                      cell. Spores, when placed in an
                                           environment favourable to growth,
Nearly all the changes which take          form new vegetative cells. Spores
place in the flavour and appearance        forming bacteria cause trouble in the
of milk, after it is drawn from the cow,   dairy industry because of their
are the result of the activities of        resistance to pasteurization and
micro-organisms. Of these, the most        sanitation procedures.
important in dairying are bacteria,        Moulds are multi-cellular, differing
mould, yeast and virus – the first on      greatly in most respects form
predominating. Micro-organisms are         bacteria. Although the individual cells
visible only with the aid of a             are not visible to the naked eye, at
microscope. A few are desirable            maturity they may be observed
while most cause undesirable               readily as “Mycelium”. They are
changes, a relative small proportion       found in soil, feeds, manure and
are disease-producing types, and           poorly-washed utensils. Most spores
are called “pathogens”. In the dairy       of moulds are destroyed by
industry considerable spoilage is          pasteurization.     They     are     of
expended in controlling micro-             considerable importance in cheese-
organisms which cause spoilage.            making and are responsible for some
The greater the bacterial count in         defects in butter and other milk
milk, the lover is its bacteriological     products.
quality. Bacteria are microscopic,         Yeasts are unicellular but are
unicellular fungi (plants without          somewhat large in size than bacteria.
chlorophyll) which occur principally in    Spores of yeast are readily
the form of spherical, cylindrical or      destroyed during pasteurization.
spiral cells and which reproduce by        Viruses include ultra-microscopic
transverse fission. In milk and its        forms of life. In the dairy industry,



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Dairy Technology                                                   Composition of milk



only those viruses those are parasitic           is influenced by the following
on lactic acid bacteria and known as             factors: (i) Food Supply. Milk
Starter Bacteriophage (or simply                 and most dairy products
Phage) are of special importance.                furnish      all    the     food
The viruses range in size. The                   requirements        of    micro-
viruses range from 0.22 to 0.23                  organisms, (ii) Moisture: Milk
microns. The lactic phages are                   contains adequate moisture
usually not destroyed by normal                  (dry products, due to their low
pasteurization of milk employed for              moisture       content,     keep
cheese and cultured buttermilk, but              longer), (iii) Air: supplies
they can be destroyed by higher heat             oxygen to aerobic types of
treatment.                                       bacterial and to moulds in
                                                 general, (iv) Acidity or pH:
B.     Growth of Micro-organisms.                Most common types prefer a
In microbiology, growth refers to                pH from 5.8 to 7.5. (v)་
increase in numbers. Milk drawn                  Preservatives: These check or
from a healthy cow already contains              destroy growth depending on
some      bacteria.    Their   number            their concentration (vi) Light:
multiplies during production and                 Is more or less harmful. (vii)
handling,      depending     on     the          Concentration: High sucrose
cleanliness of these operations.                 or salt content in product
Subsequently, their number may                   checks growth and (viii)
grow still further (either substantially         Temperature: An important
or only slightly) depending on                   means for controlling growth.
storage conditions.                              Each species of micro-
The changes which take place in the              organism has its optimum,
physio-chemical properties of milk               maximum         and     minimum
are the result of the activities of the          temperatures       of    growth.
individual microbial cells during their          According to their optimum
period of growth (development and                growth temperatures, bacteria
reproduction) or of substances                   can be classified into:
produced during such activity.
                                           Psychotropic:     Can     grow     at
a.       Stages of Growth. The growth      refrigeration temperature (5 – 7 0C).
         of micro-organisms normally       Mesophylic:        can     grow    at
         takes place in the following      temperatures ranging between 20 0C
         stages: (i) initial stationary    to 40 0C. Thermophylic (Heat loving):
         phase; (ii) lag phase (phase of   Can grow at temperatures above 50
                                           0
         adjustment); (iii) accelerated     C.
         growth phase (log phase); (iv)
         maximum stationary phase          Note: In general, low temperatures
         and (v) phase of accelerated      (below 10 0C) retard microbial growth.
         death.                            Hence milk and dairy products
                                           should be adequately refrigerated to
b.       Factors influencing growth:       prevent rapid spoilage. The optimum
         the growth of micro-organisms     growth rate of the majority of micro-



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Dairy Technology                                                               Composition of milk



organisms    will be    found   at
                              0
temperatures between 15 to 38 C or            (v)            Ropiness. Long threads of
above.                                                       milk are formed while pouring.

c.       Products of microbial growth:        (vi)           Sweet Curdling. Due to
         These are: (i) Enzymes;                             production of a rennin-like
         (ii) decomposition of products                      enzyme, which curdles milk
         (fat, proteins, sugars, etc.)                       without souring.
         (iii) pigments, (iv) toxins and
         (v) miscellaneous changes.           C.             Destruction      of        Micro-
                                                             organisms
d.       Results of microbial growth in
         milk.                                This may be done by means of:

These are:                                           (i)        Heat. Most widely used.
                                                                Different types of heat
(i)      Souring.     Most     common,.                         treatment     (temperature-
         Caused by transformation of                            time combination) are
         lactose into lactic acid and                           employed,       such       as
         other volatile acids and                               pasteurization, sterilization,
         compounds, principally by                              etc.
         lactic acid bacteria. (The
         development of sour acid                    (ii)       Ionizing Radiation. Such
         flavour is not due to lactic acid,                     as ultra-violet rays, etc.
         which is odourless, but due to
         volatile acids and compounds).              (iii)      High frequency sound
                                                                waves. Here, the micro-
(ii)     Souring     and  gassiness:                            organisms are destroyed,
         Caused by Coli group, which                            actually by the heat
         are commonly found in soil,                            generated.
         manure, feed, etc. and
         therefore           indicate                (iv)       Pressure. Should be about
         contamination of milk and                              600 times greater than
         dairy products.                                        atmospheric pressure and

(iii)    Aroma production. Due to                    (v)        Chemicals. These include
         production of desirable flavour                        acids, alkalis, hydrogen
         compounds such as diacetyl                             peroxide, halogens, etc.
         (in ripened cream butter).

(iv)     Proteolysis.          Protein        Milk and Public Health
         decomposition   leading to
         unpleasant             odours        It is well established that milk can be
         (Sometimes desirable flavours        a potential carrier of diseases
         may develop, as in cheese            producing organisms. Milk-borne
         curing).                             epidemics have occurred in the past



Prepared by Tshewang Dorji                                                                    10
Dairy Technology                                                      Composition of milk



throughout the world. Unless proper         Safeguarding the Milk supply
precautions      are     taken,  such
outbreaks of milk-borne diseases            Whereas       “cleanliness”    implies
can occur anywhere, any time,               freedom from extraneous matter
especially it raw milk is consumed.         (such as manure, dust, etc.), “safety”
                                            means freedom form pathogenic
Diseases which are know to be               micro-organisms.       For     human
transmissible through milk are listed       consumption, milk that is both clean
which they may enter the milk.              and safe is highly desirable.

(i)      Infection of milk directly from    The sanitation of the milk supply can
         the cow. These diseases are        be safeguarded in two ways:
         essentially      bovine.    The
         causative organisms enter the
         milk through the mammary           (a) Production and handling of raw
         glands or through faecal               milk in such a manner as to
         contamination and may cause            prevent its contamination by
         a diseased condition in milk.          pathogenic organisms. This will
         Examples:                Bovine        require
         tuberculosis, Undulant fever,
         diphtheria, etc.                   (i)     Ensuring the health of dairy
                                                    cattle by various control
(ii)     Infection from man to cow and              measures
         then to milk. These diseases
         are essentially human but can      (ii)    Safeguarding the health of
         become established in the                  employees by regular medical
         cow’ udder. Examples: septic               examination
         sore throat; Scarlet fever,
                                            (iii)   Protection of water supply
         Diphtheria, etc.
                                                    from     contamination by
                                                    pathogenic organisms
(iii)    Direct contamination of milk
         by human beings. These are         (iv)    Flies and their control
         human        diseases,       the
         pathogenic     organisms      of   (b) Pasteurization of milk, so as to
         which enter the milk through       kill all pathogenic organisms and
         contaminated bottles or other      avoidance of any post-pasteurization
         utensils, water supply, insects    contamination.
         and dust. Examples: Typhoid
         or      Paratyphoid       fever,
         dysentery or Diarrhoea, etc.




Prepared by Tshewang Dorji                                                           11

				
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