This document summarizes key information about microorganisms found in milk and milk products. It discusses the study of dairy microbiology and describes the normal microfloral found in milk. Important microorganisms like bacteria, yeasts and molds are examined in more detail. Various biochemical types of microbes are defined based on how they affect milk, including acid producers, gas producers, and proteolytic or lipolytic types. Common fermented milk products like yogurt, curd and butter are also summarized.

1. DAIRY
MICROBIOLOGY
• Microorganisms in milk
• Milk products.

2. Dairy microbiology
◦ Study of microorganisms in relation to milk and milk products.
◦ It deals with normal microbial flora of milk ,pasteurization, making dairy products.

3. MILK
◦ White, fresh, clean.
◦ Primary source of nutrition.
◦ Liquid forms
◦ It contains water, fat, protein and lactose.
◦ Provide growth to microorganisms.

4. PHYSICAL AND CHEMICAL PROPERTIES
OF MILK
◦ Milk is a white emulsion or colloid or butter fat globules.
◦ It contains many other nutrients.
◦ It contains 30-35 grams of protein.
◦ Different carbohydrate including lactose, glucose, galactose and other oligosaccharides.
◦ Ca, mg, Na, k, citrate and cl all are included.
◦ Vitamins A, B,C,D,E, thiamine, biotin, riboflavin are all present in milk.

5. MICROORGANISMS
IN MILK

6. MICROORGANISMS IN MILK
◦ Excellent nutrient for microbial growth.
◦ Supports the growth of a variety of bacteria including pathogens.

8. IMPORTANT MICROORGANISMS IN
MILK
◦ Bacteria
◦ Yeasts
◦ Molds.

9. BACTERIA

10. BACTERIA
◦ Major section of microorganisms.
◦ Study of bacteria in relation to milk and milk products- DAIRY BACTERIOLOGY.
◦ Produce desirable and undesirable changes in milk and milk products.
◦ Eg: Bacillus subtilis.

11. YEASTS
◦ Act on lactose and produce ACID and CARBONDIOXIDE
◦ SOURCE: feed, soil.
◦ Lipolytic in action.
◦ EG: Torula cremoris, Torula lactis, Saccharomyces cerevisiae.

12. MOLDS

13. MOLDS
◦ Undesirable odour.
◦ Contaminate and grow in large numbers on the surface of butter, cream, khoa and cheese.
◦ Colour- black, grey, blue or white.
◦ Proteolytic/lipolytic.
◦ EG: Penicillium sp.

14. CLASSIFICATION
classification.
Biochemical type temperature characteristics pathogenic type

15. BIOCHEMICAL TYPE OF
MICROORGANISMS
◦ Acid producers
◦ Gas producers
◦ Ropy or stringy fermentation type
◦ Proteolytic type
◦ Lipolytic type
◦ Acetic acid type
◦ Butyric acid
◦ Production of abnormal colour in milk.

16. BIOCHEMICAL TYPES
Acid producers
◦ Produces acid.
◦ EG: STREPTOCOCCI: It is a spherical bacteria.
Streptococcus lactis- produce normal souring of milk.
Streptococcus cremoris – good flavor to ripened cream.
Streptococcus thermophilus – occurs in pasteurized milk. It is used in yoghurt preparation.

17. BIOCHEMICAL TYPES
Acid producers
◦ COLIFORMS:
◦ Source- manure, polluted water, soil and plants.
◦ It is a facultative anaerobes.
◦ It cause rapid spoilage to milk.
◦ EG: E. coli.

18. BIOCHEMICAL TYPES
Gas producers
◦ Form ferment lactose with the accumulation of gas.
◦ These gas may be carbon dioxide/ mixture of carbon dioxide and hydrogen.
◦ EG: Coliform sp, clostridium butyricum, Torula cremoris.

19. BIOCHEMICAL TYPES
Ropy or stringy fermentation type
◦ SOURCES: soil, water, plants and food.
◦ Synthesize a viscous polysaccharide material.
◦ Eg: Alcaligenes viscolactis, Enterobacter aerogenes.

20. BIOCHEMICAL TYPES
Proteolytic microorganisms
◦ Coagulate casein by the enzyme RENIN.
◦ SOURCES – soil, water and utensils.
◦ Responsible for sweet curdling and peptonization of milk.
◦ EG: Bacillus subtilis, Bacillus cereus, Pseudomonas sp., Streptococcus liquefaciens.

21. BIOCHEMICAL TYPES
Lipolytic type
sources – soil, water, dairy utensils.
• Hydrolyze milk fat into glycerol and fatty acids.
• Some fatty acids produce rancid odour and taste to milk.
• EG: Pseudomonas fluorescenes, Candida lipolytica, Penicillium sp,

22. BIOCHEMICAL TYPES
Acetic acid type
◦ Combination with yeasts and lactic acid bacteria.
◦ EG: Acetobacter aceti, Acetobacter kutzingianum, Acetobacter pasteurianum.

23. BIOCHEMICAL TYPES
Butyric acid
◦ SOURCES- faeces, soil, water.
◦ Eg – Bacillus welchii
◦ Produce butyric acid and small quantities of propionic acid, formic acid, hydrogen, carbon
dioxide,.
◦ Milk is curdled slowly.

24. BIOCHEMICAL TYPES
Production of abnormal colour in milk
◦ Certain bacteria produce abnormal colour when they grow in milk. When such milk is exposed
to air, it leaves carbon dioxide and absorbs oxygen.
◦ EXAMPLE- Bacillus cyanogenes- produce dirty brown colour in sterile milk. Torula
glutinus- pink or red colour. Bacillus
prodigiosus- red colour.

25. TEMPERATURE CHARACTERISTICS OF
MILK
◦ Psychrophilic type- bacteria grow at very low temperature. EG- Flavobacterium sp.,
◦ Mesophilic type- organisms grow at moderate temperature between 10 and 30’c. EG-
Streptococcus sp.,
◦ Thermophilic type- well in temperature above 30’c.EG- Bacillus sp.,
◦ Thermoduric type- grow at above 62’c and can survive even after pasteurization. EG-
Microbacterium lactis, etc.

26. PATHOGENIC TYPE OF BACTERIA MILK
o Source- cow/man.
o Milk-borne disease.
o EG- Streptococci . When cows are infected with streptococci in the udder ,it will transfer into
milk and cause diseases.

27. MILK PRODUCTS

28. Milk products
◦ Products synthesized from milk – MILK PRODUCTS/ DAIRY PRODUCTS.

29. MILK PRODUCTS

30. CHARACTERISTICS OF FERMENTED
MILKS
FERMENTED
PRODUCT
RAW MATERIAL MICROORGANISM
RESPONSIBLE FOR
FERMENTATION
REMARKS
Cultured butter milk Pasteurized skim
milk
Streptococcus lactis
Leuconostoc citrovorum
Lactic acid fermentation
kefir Whole milk Streptococcus lactis
Lactose fermenting yeast
Alcoholic and lactic acid
fermentation.
Kumiss Mare’s milk Lactobacillus bulgaris
Streptococcus lactis
A mixed acid-alcoholic
fermentation products
using mare’s milk (in Russia)
yogurt Whole milk Streptococcus
thermophilus
Lactic acid fermentation

31. IMPORTANT FERMENTED MILK
A number of milk products viz., cheese, yogurt, milk powder, cream, butter, etc., are produced
from milk.
o Examples of milk products: 1)YOGURT

33. YOGURT
◦ Turkish word- JUGURT.
◦ Most popular fermented milk
◦ Made from skimmed milk, milk .
◦ Milk should be free from contamination.
◦ Example: Lactobacillus bulgaricus, Lactococcus thermophilus helps to produce yogurt.

34. YOGURT
◦

35. CURD
o Fermented milk product.
o Pasteurized milk or boiled milk
o Fermented by harmless lactic acid bacteria or other bacterial culture which is retained from the
previous days curd (starter).
o Two types- churning into desi butter, direct consumption prepared from whole milk or skimmed
milk.

36. BUTTER
◦ Fat concentrate
◦ Obtained by churning cream or curd with or without salt.
◦ Example- Desi butter.
◦ Butter with 10 yeasts and molds per gram and less than 50 proteolytic bacteria per gram is
considered as GOOD BUTTER.
◦ Eg-Leuconostoc citrovorum.

37. ACIDOPHILS MILK
◦ Whole or skimmed milk is fermented with Lactobillus acidophilus which have benefits in the
gastrointestinal tract.

38. CHEESE
◦ It is a milk product produced by separating casein from milk. The rest of the milk is in the form
of whey.
◦ Classification:
1. On the basis of coagulation
2. On the basis of hardness.

39. MANUFACTURE OF CHEESE
◦ INOCULATION OF MILK
◦ CURDLING
◦ PROCESSING OF CURD TO REMOVE MOISTURE
◦ SALTING
◦ RIPENING

40. THANK YOU