Microbiology of milk for diploma level students

1. UNIT 5 : Microbiology of
milk

2. Dairy microbiology may be defined as the branch of microbiology,
which deals with the activities of the microorganisms in the milk
and milk products.
Milk and milk products are very good culture media for the
growth and development of a number of microorganisms some
are desirable and others are harmful and pathogenic.
In the process of handling and distribution milk is easily
contaminated. Nearly all of the changes, which take place in the
test, odor, and appearance of the milk after it is drawn from the
cow, are the result of the activities of microorganisms.
Microorganisms found in milk are bacteria, fungi, molds , viruses
etc.

3. Type of microorganisms found in milk :
a. Bacteria
1. The acid producing bacteria: - Those bacteria which are responsible for
conversion of lactose to lactic acid are include in this group
Streptococcus lactis
Streptococcus cremoris
Lactobacillus acidophillus
2. Aroma producing bacteria: - Bacteria of this group are responsible for the
production of desirable aroma and flavor in milk product. These bacteria utilize
citric acid and lactic acid which contribute to the flavor and aroma.
Streptococcus citrovorus
Streptococcus paracitrovorus
3. Gas producing bacteria: - These are harmful type of bacteria ferment lactose
and produce acid & gas. Along with lactic acid and CO2 gas they produce bad
odors and flavor in milk and milk product.
Eschericha coli
Aerobacter acrogenes

4. 4. Peptonizing type of bacteria: - The bacteria, which show a
tendency to break down the casein by a process known as
proteolysis. As a result off flavor and unpleasant odors appear in
the milk. These groups of bacteria are: -
Bacillus subtilis
Bacillus mycoides
5. Ropiness type of bacteria: - These are a number of bacteria,
which are able to bring about a peculiar change in milk, or these
organisms form gum-like substance. These are: -
Alligenes viscosus
Alcaligenes viscolactis
6. Toxins producing bacteria: - These bacteria are producing
poisonous compounds in the dairy products known as toxins. They
may cause serious disturbances in the well being of man or of
animal such as Salmonella, Streptococcus etc.

5. b. Fungi : Aspergillus, Fusarium , Penicillium – They
produce mycotoxins.
c. Virus : Bacteriophage, FMD virus , cowpox virus ,
papilloma virus
d. Mucor : Rhizomucor, Rhizopus

6. Significance of microorganisms in milk
Information on the microbial content of milk can be used to judge
its sanitary quality and the conditions of production.
Certain microorganisms produce chemical changes that are
desirable in the production of dairy products such as cheese,
yoghurt.

7. Use of microorganisms in dairy industry are as follows:
Useful microorganisms for dairy industry are as follows:
1. Dahi
 Streptococcus lactis
 Streptococcus cremoris
 Lactobacillus bulgaricus
2. Yogurt
 Lactobacillus bulgaricus
 Streptococcus thermophillus
 Acidophillus milk
 Lactobacillus acidophillus
3. Cheese making
 Streptococcus lactis
 Streptococcus cremoris
 Streptococcus thermophillus
 Lactobacillus bulgaricus
 Penicillium camemberti

8. 4. Cream
Streptococcus lactis
Streptococcus cremoris