This document discusses the microflora found in raw milk and methods for controlling milk contamination. It begins by introducing milk and its nutritional properties. It then describes the various microorganisms commonly found in raw milk, including both harmless and potentially pathogenic bacteria. The primary sources of milk contamination on farms and during processing are explained. Control methods focus on cleanliness of animals, milking equipment, storage and processing facilities. Preservation techniques to limit bacterial growth include pasteurization, refrigeration, freezing, drying, and adding preservatives. Proper application of good manufacturing practices and hazard analysis critical control point guidelines are emphasized for effective contamination control.

1. Microflora of raw milk.
Sources of milk contamination and
their control.
SUBMITTED TO- SUMBITTED BY-
Dr. Paras Porwal Shaista Khan
Assistant Professor MSc. MB. 3rd Semester.
AIB. A07199319007.

2. Introduction-
Milk is a white nutrient-
rich liquid produce by
mammary glands of
mammals.
Primary source of nut-
rition for young ones.
Around 6 billion people
consumed milk products, globally.

3. Properties of Milk -
• White emulsion or colloid of butter fat globules.
• Fat globules and small casein micelles imparts
opacity.
• Yellow-orange carotene provide creamy yellow
colour.
• Contains 30-35% protein per litre of milk, 80% of
which is arranged in casein micelles.
• Oligosaccharides, vitamins ( A, B6, B12, C,D, K),
minerals (calcium, Magnesium, etc.) are also present.

4. MICROORGANISMSIN RAWMILK -

5. • Milk is sterile at secretion in the udder but it
gets contaminated by several bacteria as it
leaves the udder.
• Further the number of microflora in milk can be
increase during milking, handling, storage and
other pre-processing activities.
• Supports the growth of several bacteria
including the pathogenic bacteria.

6. • Alkali-forming bacteria –
• Aerobic , spore forming bacilli. Renders the milk
alkaline.
• Eg- Alkaligenes spp. Achromobacter.
• Proteolytic bacteria –
• Produces proteolytic enzymes, hence causes
bitterness and putrefaction.
• Eg- Bcillus subtilis, Proteus vulgaris,
Pseudomonas, Staphylococcus micrococci, etc.

7. • Gas-forming bacteria-
• Produces acid and gas, resulting in the spoilage
of milk.
• Eg- Coliform bacteria, Cl. Butyricum, etc.
• Acid-forming bacteria –
• Ferment lactose, forms the lactic acid and leads
to the formation of curd.
• Eg- Streptococcus lactis, Str. Faecalis lactobacilli,
Lactoacid bacteria, etc.
• Presence of inert bacteria shows no visible
change.

8. Leuconostoc bacteria-
• Facultative anaerobes coliform bacteria, with an
optimum growth at 37 degree celsius.
• Can be associated with the presence of milk but not
themselves are pathogens.
• Can cause spoilage of milk as they produce gas and
acid resulting in the fermentation of milk.
• Killed by HTST method.
• Eg- Escherichia coli.

9. Pathogenic microroganisms in milk -
• There are some pathogenic bacteria still of concern
in raw milk :-
• Yersinia enterocolitica.
• Bacillus cereus.
• Salmonella spp.
• Campylobacter jejuni.
• Listeria monocytogenes.
• E. coli 0157:H7.

10. Moulds-
• Species of Aspergillus, Penicillium, and Fusarium can
grow in milk and its products.
• On favourable conditions, these moulds can produce
mycotoxins which can lead to a health hazard.

11. SOURCESOF MILK CONTAMINATION
AND THEIRCONTROL-

12. Sources of Contamination -
1) From the farm-
• During the process of milking, the milk is
contaminated by the surrounding areas.
• Bacteria normally present in soil, manure, and
water may enter from this source.
• The other two most important sources of
contamination are milk-contact surfaces and dairy
milk utensils.

13. Contd.
• These includes milking machines and milk pail.
• The bacteria from these sources involove
psychrotrophic (gram negative rods),
thermodurics (eg- Micrococcus, Streptococcus,
Clostridium, etc.), Coliform bacteria.
Other sources of contamination –
• Hands or arms of the dairy workers or milker.
• The air of the milk parlour or the barn.
• The flies, if present any.

14. 2) At the manufacturing level –
• After the farm, the other possible
contamination may occur via transfer pipes,
sampling utensils, transfer trucks, and the
equipments use for the processing.
• Tank pumps, pipelines,vats,valves, and
separators are the major possible sources of
conatmination.
• The level of contamination is depend on the
sanitizing and cleaning methods.

15. Control method-
• Animal Cleanliness
• All animals should be kept clean.
• All lying areas should be of sufficient size and should
be kept clean and dry.
• Passageways and access routes should be free from
accumulations of dung and slurry.
• Fields, tracks and gateways should be well
maintained and kept free from accumulations of
dung, slurry and mud.

16. •Milking Practices
 Milk from each animal must be examined for
physical/chemical/organoleptic abnormalities and where
abnormal milk is detected this milk must be rejected.
 Teats, udders and adjacent parts must be clean before
milking.
 Hands, contact surfaces and milking equipment must be
kept clean at all times.
• Milking Equipment
 Milk contact surfaces must be appropriately cleaned and
disinfected immediately after each milking.
 All equipment must be kept clean and in good condition.

17. •Milk Storage and Cooling
 Milk must be protected from contamination during transfer
and storage.
 Milk must be cooled quickly to minimise bacteria
multiplication.
 Bulk tanks must be cleaned and disinfected after each milk
collection and kept in good condition.
 “ these control lies in the guidelines of GMP and HACCP
method of food safety.”
• Where GMP stand for Good Manufacturing Process and
HACCP stand for Hazard Analysis and Critical Control Point.

18. Preservation methods -
1. Asepsis.
• Prevention as far as is practical of the contamination of
milk is important in its preservation.
2. Removal of microorganisms.
• After microbes have entered milk, it is difficult to
remove them effectively. So, the process of
centrifugation, as in clarifying or separating, will
remove microbes from milk.
3. Use of heat (pasteurization and Ultra-pasteurization).
• Pasteurization temp- 72 degree celsius for 15 seconds.
Ultra-pasteurization temp- 130 degree celsius for 1 sec.
or more.

19. Contd..
4. Steam Under pressure.
• Evaporated milk is canned and then heat-processed by
steam under pressure. The forewarming of milk at 93-100
degree celsius before evaporation kills even resistant
bacterial spores.
5. Use of Low temperature (freezing, refrigerated storage).
• Refrigerated storage- raw milk for pasteurization cooled at
10 degree celsius or less within 2 hrs after being drawn and
kept that cold until processed.
• Freezing- pasteurized milk has been frozen at about -28 to -
29 degree celsius and shipped.
6. Drying (condensed products and dry products).
7. Use of preservatives (sugar).

20. Thank you