3. INTRODUCTION
• Cow’s milk has been defined as the secretion, excluding colostrum, which can be
gained by normal milking methods from lactating mammary gland of the healthy,
normally fed cow.
• Milk containing three basic components,
1. Water
2. Fat
3. Non-fatty solids (NFS) or solids not fat (SNF).
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4. AVERAGE PERCENTAGE COMPOSITION OF THE MILK OF THE COW AND OTHER
MAMMALS ARE SHOWN IN TABLE BELOW
Mammals Water Protein Fat Lactose Ash
Cow 87.2 3.4 3.6 4.9 0.71
Human 87.6 1.2 3.8 7.0 0.21
Buffalo 82.4 4.7 7.4 4.6 0.78
Camel 87.6 3.4 3.0 5.1 0.71
Dog 74.5 3.1 10.2 11.3 0.80
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5. THE NORMAL QUALITY CHECKING PARAMETERS
OF MILK
• Acidity and pH
• The pH is usually between 6.4 and 6.6.
• The total acidity of freshly drawn milk is usually about 0.14 percent (as lactic
acid). On storage, the acidity increases due to the action of micro-organisms.
• Mineral matter
• The total ash of genuine milk varies from about 0.71 to 0.75 percent.
• Vieth’s ratio
• For milk containing a normal amount of SNF 8.4-8.7 percent the ratio of lactose
(hydrated): protein: ash is most exactly 13:9:2. This is known as Vieth’s ration and as it is
unaffected by the removal or addition of water
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6. • Untreated milk accredited as free from brucellosis. It is required to satisfy the
methylene blue test.
• Pasteurised Milk shall be either retained at 62.8°-65.6C for at least 30 min or be
retained at not less than 71.7°C for at least 15 sec. Satisfy the methylene blue and
phosphatase test.
• Sterilized Milk is heated to and maintained at not less than 100°C for such a period
that it will comply with the turbidity test. Satisfy a colony count test.
• Ultra Heat Treated Milk retained at a temperature of not less than 132.2°C for not
less than 1 sec and shall be filled and sealed aseptically into the sterile containers.
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7. • An infrared milk analyser show peaks near 5.8, 6.8 and 9.6 µm corresponding to
these fat, protein and lactose.
• The specific gravity of milk varies according to the proportions of fat specific
gravity 0.93, NFS specific gravity 1.614 and water. The density of milk can be
conveniently measured by mean of the lactometer
• The percentage of fat is determined by gerber method the total solids figure can
be calculated from the modified Richmond’s formula
T=0.25D + 1.22F + 0.72
• D=the BS density hydrometer reading at 20°C,
• T=total solids (percent) and
• F= fat (percent) so, SNF=T-F for routine purpose usually reported to the nearest
0.05 percent.
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8. ADULTERATION IN MILK
• The quality of milk is occasionally reduced by the accidental or deliberate
abstraction of fat or addition of water.
• Adulteration of milk is addition of cheaper and resembling substances to milk or
removal of one or more constituents (like fat) in order to make extra profit is called
adulteration.
• Adulteration can be from improper use of additives, e.g. preservatives, colours,
thickeners and from contaminants such as detergents, disinfectants, antibiotics and
dirt.
• The average freezing point of bulk milk is -0.544°C but it may vary between -
0.530 and -0.560°C is acceptable.
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9. DETERMINATION OF THE FREEZING POINT DEPRESSION OF MILK
• 1.Hortvet method
• Calibration of the Hortvet thermometer
• Standardise the Hortvet thermometer with water and against pure sucrose or salt
solutions using the procedure for milk.
• Obtain the mean freezing point depression for each sucrose solution by
subtraction from the mean of those for water.
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12. Method
• Determine the acidity of the milk. If it is exceeds 0.3 percent m/v as lactic acid, the
determination of freezing point depression should be abandoned. Cooling bath is
maintained -2.5 to -3.0°C.
• Freezing point of water: pour 45±1ml of distilled water into the freezing tube and
start the stirrer until indicates a temperature of -1.3±0.05°C
Keep stirring until the Hortvet thermometer indicates a rise in temperature
and remove the freezing starter tube
take the reading stir 3 times and tap 7 times and read as before. The
second and third readings should not differ by more than 0.002°C
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13. • Freezing point of milk: Rinse the tube, thermometer and stirrer with a portion of
the cooled milk sample.
• Then pour 45±1ml of milk cooled to 0-5°C into the freezing tube the reading on
the thermometer has fallen to -1.65° The second and third readings should not
differ by more than 0.002°C.
• The freezing point depression of the milk (FPD) is the algebraic difference obtained
by subtracting the thermometer reading for milk from that of water.
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14. Dirt in Milk
The determination of dirt in milk all insoluble matter and foreign material to milk as
it leaves the udder
• Milk sample is covered sedimentation vessel connected to a standardised
centrifuge tube
• Stand for 72 hours after filling of milk
• The centrifuge tube is removed and spun at 2000rpm for 5 min
• Separate the dirt and again centrifuge for 3 min
• Then washing with ammonia and hydrochloric acid
• The volume of moist dirt is read off in the calibrated tube
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15. Preservatives in Milk
Preservatives have seldom been reported as being present in milk in recent years.
Preservatives used are hydrogen peroxide, benzoic acid, fluoride, salicylate, β-
naphthol, sodium carbonate and glycerine.
Determintion of boric acid
• make about 5 ml of the milk just alkaline with lime water
• evaporate and ignite the residue, acidify the ash with hydrochloric acid and dip
into the liquid a piece of turmeric paper
• dry it on the water bath paper turn pink or red
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16. Determination of Formaldehyde(Hehner’s test )
• sulphuric acid which contains a trace of iron is added to sample
• A violet colour is produced
Benzoic acid, propyl-hydroxybenzoate and sorbic acid in milk have been
determined spectrophotometrically
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17. CONTAMINANTS IN MILK
1. Hypochlorite may be present in milk due to its being for disinfecting utensils.
Hypochlorites (Sodium hypochlorite NaOCl) may be detected by the following
test
• To 3ml of milk in a test tube add 3 ml of 73.5 percent sulphuric acid containing
0.025 percent stannous chloride
• Shake in a freezing mixture of ice and salt, allow to stand in the mixture for 3
minutes and then centrifuge at 2500 rpm for 3 minutes
• examined under ultra violet light yellow fluorescence
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18. 2. Quaternary ammonium compounds (QAC) (Benzalkonium chloride) may be
present in the milk due to same residual detergent solution remaining after bottle
washing.
• Indicator solution: Prepare a stock solution by dissolving 0.05g eosin in 100ml
acetone. Shake 10 ml of stock solution with 90 ml of tetrachloroethane and 1 g of
citric acid and filter.
• Buffer solution: dissolve 25 g citric acid in 100 ml water and adjust to pH 3-5 with
50 percent sodium hydroxide solution (approximately 12 ml required)
• To a centrifuge tube add 1ml milk, 5ml water, 1ml indicator solution and 0.2ml
buffer and shake hard for 10sec.
• centrifuge for 5 min at 3200 rpm. If QAC is present the bottom layer assumes a
red colour
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19. 3. Iodophors (Povidone Iodine) can be detected by the blue colour formed with
benzoflavone and hydrogen peroxide.
4. Artificial colours. Unless described as Flavoured milk
• annatto can be detected by pouring a few ml of milk into a flat dish and adding
sodium bicarbonate solution. Then a strip of filter paper is inserted. After some
hours the paper is stained brown in the presence of annatto and turns pink on the
addition of a drop of stannous chloride solution.
• The presence of azo dye usually gives a pink colour on the addition of
hydrochloric acid to the milk or, better to the coloured curd.
• Sucrose can be detected by paper chromatography, TLC or by formation of HMF
after hydrolysis.
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20. • Antibiotics in Milk
Antibiotics are frequently used for the treatment of cows suffering from
mastitis and traces may be present in the milk for three days after the last treatment.
Detection of Penicillin
Various techniques for detecting antibiotics in milk including microbial assay
at dye marking methods and the TTC test
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21. • TTC: The milk sample is heated to 95°C to inactivate naturally occurring inhibitory
substances then cooled.
• The streptococcus thermophilus, bromocresol purple indicator an appropriate
nutrients are added.
• Upon incubation at 45°Cfor 4 hours
• Acid is produced in antibiotic free milk which turns the indicator yellow. In the
presence of antibiotic the indicator remains blue. The failure point of the test is
equivalent to a penicillin level of 0.02iu/ml
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22. Test for different types of milk
HEAT-TREATMENT OF MILK
i. Methylene blue test be applied to untreated and pasteurized milk.
ii. The phosphatase test is prescribed for assessing the efficiency of
pasteurization
iii. The turbidity test is applied to sterilized milk.
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23. • Methylene blue reduction test
1. sample shall be mixed thoroughly transferred to a test tube up to the 10 ml mark 1
ml of methylene blue solution shall be added and closed with stopper
2. kept the test tube in a water bath, and its temperature which shall be between 37°C
and 38°C
3. A control tube shall be used for comparison add tap water and decolourised of milk
measured, completely decolourised or is decolourised up to within 5 mm of the
surface
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24. • The Resazurin test
1. The resazurin dye used changes from blue in the oxidized state through various of
pink to colourless.
2. more sensitive than methylene blue for revealing faults in certain milk.
• The Phosphatase Test
1. incubation of the milk with disodium p-nitrophenyl phosphate under alkaline
conditions
2. Milk contains phosphatase a yellow colour is produced due to the formation of p-
nitrophenol
3. comparing the colour produced with the standard colours on an APTW comparator
disc
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25. • The Turbidity Test
For sterilized milk the sample is shaken with ammonium sulphate, filtered and
the filtrate is then heated
Any albumin which is still present in solution due to insufficient heat
treatment during manufacture will reveal itself as a turbidity in the heated filtrate
The test is not prescribed for UHT milk, which gives a slight turbidity
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26. CONCLUSION
• Milk is an essential food, which is consumed by all age people as to drink or in
form of some milk products. It is essential to know the possible contaminants and
adulterants of milk to ensure quality of it before consuming. FSSAI have set safety
standards for milk to be followed that have been given out to states. Every state
has food safety commissioners who are supposed to keep a check on the quality
of milk. (Adulterants is a broad category and even water in milk will be called an
adulterant, but that does not mean it is unsafe milk) The main contaminants in
milk as per the FSSAI is Aflatoxin-M1, Antibiotics and pesticides. The main
adulterants in milk as per the FSSAI is Urea, Detergents, Hydrogen peroxide and
Neutralizers. Ensuring the limits of these agents would confirm the quality of milk
for consumption
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