The Milk Microbiology ppt is useful to the under graduate students. This ppt may help to summarize the studied content related to the mentioned points in the given collection of slides.

1. Milk Microbiology
Dr. Deepak U. Bhusare
Assistant professor
Department of Microbiology
Digambarrao Bindu ACS College,
Bhokar Dist. Nanded (MS), India

2. Introduction
 Milk is a highly nutritious media for bacteria, it can
spoil easily.
 Initially milk have few organisms, but bacteria can
enter milk during milking process and handling.
 Refrigeration improved milk industry, but still other
improvements needed to be done to reduce No’s of
non pathogenic bacteria.

3. Composition of Milk
Content Percentage (%)
Water 87.0
Proteins 3.5 (Casein & Whey)
Fat 3.5 to 3.7
Carbohydrates 4.9 (Lactose)
Vitamins Niacin, Ribofavin, Thiamin, Vit.
B6 Vit. A & D
Minerals Ca, P, Mg, K, Na etc.
Enzymes Lipase, Proteases, Peroxidase

4. Milk
Water Total
solids
Fat
Trigly
cerides
Phosp
holipid
s
Steroles
Fat soluble
vitamins
(Vit: A, D,
E, K)
Solid not Fat (SNF)
Nitrogenous
components
Protein
s
Casein, K-casein,
Immunoglobulin
Non
Protein
s
Carbohydrates
Lactose &
Other
Oligosacchar
ides
Minerals
Ca, Mg, P,
K, Cl, So4
Enzymes
Protease, Lipase,
Catalase, Amylase
Vitami
ns

5. Non pathogens in milk
 Air borne contaminants: Pseudomonas, Flavobacterium,
Alcaligenes, Some coliforms, micrococcus & fungi.
 Psychrotrophs :
- More detrimental to milk.
- They are able to grow at 5°c and less and make up a
large number of the microbes in milk, they are natural soil
inhabitants and wide spread in environment esp. water.
• Spoilage of refrigerated milk consists usually of bitter,
rancid, fruity flavours.
• Spoilage of milk at room temp. consists usually of
souring.

6. Types of Microorganisms in Milk
 The Normal flora
◦ Lactic acid bacteria (LAB) (Gram Positive)
 Lactobacillus acidophilus
 L. bulgaricus
 L. lactis
 L. brevis
 L. fermentum
◦ Streptococcus species (Gram Positive)
 S. pyogens
 S. bovis
 S. thermophilus

7.  Pediococcus species(Gram positive Cocci)
◦ P. halophilus
◦ P. dextrinicus
◦ P. acidilactici
 Leuconostoc species (Gram positive Cocci):
◦ L. mesenteroides
◦ L. paramesenteroides
◦ L. lactis
◦ L. cremoris

8. Sources of Pathogens in milk
 Animal itself: Mycobacterium bovis, Brucella species,
Coxiella burneti ,Campylobacter sp.
 Humans: Salmonella, Shigella.
 Environment: Bacillus anthracis, Clostridium
perfringens, Clostridium botulinum

9. Pasteurization of milk
 LTLT : Low temp. Long time 63°C 30 minutes
 HTST: High temp. Short time72°C 15 seconds
 UHT : Ultra high temp.,130-135 °C 1 second
Pasteurization:
 Kills and removes all pathogens(100%)
 Kills most non pathogens (99%)
 Surviving organisms are spore formers, thermoduric and
thermophilic organisms

10. Pasteurization of milk
• Common thermoduric organisms: Bacillus, Micrococci,
Lactococci, Arthrobacter , Microbacteria, Corynebacteria
 Pasteurization provide a product with average shelf life 7-10
days( LTLT-HTST)
 Types and numbers of bacteria in milk depend on the
microbial load before pasteurization

11. Pasteurization of milk
 No of non pathogens in raw milk is 500,000 to
3,000,000 organisms/ml of milk
 While No of non pathogens in pasteurized milk is 2,000
to 20,000 organisms /ml
 Different methods to count non pathogens in milk such
as:
1. Viable count( pour plate method)
2. Dye reduction test
3. Direct (clump) microscopic count

12. Microbial examination of milk
1. Viable count method
2. Dye reduction test
3. Direct microscopic count

13. Viable count method
Pour plate method
 Deliver 1ml of milk to 9ml of sterile saline tube( 10-1), mix
and transfer 1ml diluted milk from tube 1 to tube 2 ( 10-2).
 Deliver 1ml of milk to an empty Petri dish ,1ml of diluted
milk 10-1,10-2 to empty Petri dishes .
 Pour 9ml of molten nutrient agar to each Petri dish, mix
well
 Leave to solidify, then incubate at 37 c 48 hrs.
 Count No of colonies and multiply by dilution factor to
determine No of viable non pathogens on milk
 A plate containing more than 300 colonies should not
counted, plate with more dilution is counted instead.

14. Advantages
 Can see cell morphology
 Count viable cell only
 Can be used to different
types of samples( milk,
milk products
Disadvantages
 Take long time
 Lots of tubes , tedious.

15. Dye reduction test
• A quick test for determination of microbial load of milk
• Use Methylene blue or resazurin dyes
• Add 1ml of dye to 10ml of milk, incubate 1 hr at 36c
• If there is change in color , it means high bact. Load .It is not
good quality milk, shorten expiration date.
• If no change in color (still blue), low bact. Load , good quality
milk , expand expiration period
• A long history of use in the dairy industry, especially to
measure microbial quality from raw milk

16. Relation between time of decolonization of
methylene blue & milk quality
Decolonization condition Quality of milk Range of bacterial
population
No decolonization within 8 hrs Excellent Zero
Decolonization within 6-8 hrs Good Very less
Decolonization within 2-6 hrs Fair Large
Decolonization within 0-2 hrs poor Very large

17. • Advantages
1. Simple, rapid, and
inexpensive
2. Only viable cells actively
reduce the dyes
• Disadvantages
1. Not all organisms reduce the
dyes equally
2. Not applicable to food
specimens that contain
reductive enzymes

18. Direct microscopic count
 Method
 Deliver 0.01 ml of milk on slide ,air dry
 Stain with LW (Levowitz- Weber )stain for 10 min.
 Count bacterial clumps with the microscope
 Reading results:
 Bacterial clump: dark blue
 Protein, Leucocytes and somatic cells :light blue background
 Fat globules : colorless
 Dirt: brown
* clump : is one cell or group of cells of same type separated by a
distance from other clumps or cells

19. Advantages
1. It is rapid and simple
2. Cell morphology can be
determined
3. Can se whole picture of
milk
Disadvantage
1. Results depends on each
analyst
2. Both viable and nonviable
are counted
3. Some bact. may not take
the stain well

20. Microbial spoilage of milk & Milk Products
• Types of Interaction of Microorganisms:
• Synergism
• Metabiosis
• Antibiosis
1. Synergism: Combined biochemical activity of two or
more organisms.
2. Metabiosis: The metabolic end product of one group
of organism are utilized as a substrate by the other.
3. Antibiosis: Growth of one organism either kills or
inhibit other organisms.

21. Spoilage of milk by Microorganisms
1. Souring (production of acidic products):
1. Streptococci
2. Coliform
3. Enterococci
4. Lactobacilli
5. Micrococci
6. Lactobacillus
7. Streptococcus are involved in excessive acid
formation.

22. 2. Gas production:
1. CO2 & H2
2. Yeast, Propionic acid bacteria and heterofermentative
lactics produce only CO2 because they lack enzyme
formate hydrogen lyase.
3. The gas formation is evidenced by foam at the top,
floating curd containing gas bubbles called Stormy
fermentation.

23. Amino acids
Peptides
Poplypeptides
Peptones
Proteoses
Proteins
3. Proteolysis:

24. Proteolytic bacteria
1. Pseudomonas fluorescens
2. P. aureofaciens
3. P. putida
4. Cytophaga
5. Lactobacillus
6. Proteus
7. Xanthomonas

25. 4. Ropiness:
◦ Ropiness caused by Alcaligens sp.
◦ Formation of galactans an oligomers or polymer with
monomeric unit of galactose.
5. Lipolysis
Fats Glycerol+Fatty acids Acetyl CoA CO2 + H2O
Lipases Beta Oxidation TCA Cycle
Saturated and Unsaturated Fatty acids Aldehydes, Organis acids Ketones etc

26. 6. Off Flavors
1. Sour/acid flavor
2. Bitter flavor: due to proteolysis & Liposysis
3. Burnt flavor: Due to Streptococcus sp.
4. Malty flavor: production of aldehydes & results in to
alcohol.
5. Fruity flavor
6. Musty potato flavor
7. Phenolic flavor
8. Rancid flavor: Due to fatty acid liberation.

27. 7. Color change:
1. Blue milk: Due to growth of P. syncyanea & Streptococcus
lactis. Some actinomycets & Molds are also forms.
2. Yellow Milk: Due to growth of P. synxantha &
Flavobacterium.
3. Red Milk: Serratia marcescens.
4. Brown milk: P.putrefaciens & by enzymatic oxidation of
tyrosine by P. fluroscens

28. Application of Microorganisms in Dairy Industry
Starter culture Fermented dairy products
Streptococcus latics and S.
cremoris
Cultured butter milk, sour cream,
dahi etc.
S. lactis Ripened cream, sour cream, butter,
cheese, buttermilk etc.
S. thermophilus yogurt
Lactobacillus citrovorum Cultured butter milk
L. acidophilus Acidophilus buttermilk
Propionibacterium Swiss cheese
Bacteria

29. Starter culture Fermented dairy products
Saccharomyces, Candida &
Debaromyces
Skyr, Kefir etc.
Yeasts
Starter culture Fermented dairy products
Geotrichum candidum Kefir
Penicillium roquefortii Cheese
Penicillium camembertii Cheese
Molds

30. Milk born diseases
1. Tuberculosis
2. Brucellosis
3. Septic sour throat
4. Streptococcal infection
5. Q-fever
All are directly added in the milk from milch animal
1. Q-fever: Coxiella burnetii
2. Brucellosis: It primarily affects goat, sheep, pigs.