This document discusses microbial spoilage of milk and milk products. It notes that dairy products are susceptible to spoilage due to their high nutritional content, water activity, and moderate pH. Common spoilage microorganisms include psychrotrophs during refrigerated storage, thermoduric microorganisms after pasteurization, and molds/yeasts after heat treatment. Sources of contamination include milking animals, equipment, and the surrounding environment. Spoilage can result in off flavors, rancidity, gas production, souring, texture changes, and discoloration. Specific microorganisms are associated with defects in products like pasteurized milk, cream, butter, cheese, and yogurt.

1. Microbial Spoilage of
Milk and Milk Product

2. Microbial Spoilage of Milk product
⬩ The loss of quality of milk and its product for its consumption due
to the microbial growth or any other microbial product is known
as Microbial spoilage of milk product.
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3. Microbial spoilage of Milk and Milk Product
• Dairy products such as milk, butter, cream and cheese are all
susceptible to microbial spoilage due to their
 high nutritional composition (Protein, Carbohydrate, Fats, Minerals,
Lactose sugar, citrate and nitrogenous compounds)
 high water activity and
 moderate pH (6.4-6.6)
 Limited self life
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4. 4
Condition of
spoilage
Type of mos Examples of mos
During refrigerated
storage
psychrotrophs Pseudomonas, Flavobacterium,
Alcaligenes, Listeria
monocytogenes, Yersinia
enterocolitica, some coliforms,
and Bacillus spp.
After pasteurization thermoduric
microorganisms
Enterococcus, Streptococcus,
some Lactobacillus, and spores
of Bacillus and Clostridium
spoilage after the
heat treatment
Molds and yeasts Aspergillus, Byssochlamys,
Cladosporium, Candida spp.

5. The source of milk contamination are:
⬩ the contamination from milking animals
⬩ the interior and exterior of the udder
⬩ the coat of the milking animals
⬩ the surrounding air of the farm and storage
⬩ the animal feed
⬩ the quality of water used
⬩ the quality of milk handling equipment and storage tanks used
⬩ biofilms formation on diary plant pipes
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6. Defects that occur in milk and milk products
⬩ Off flavor
⬩ Lipolysis with development of rancidity
⬩ Gas production
⬩ Fermentation to lactic acid with souring
⬩ Coagulation of milk protein / Proteolysis
⬩ Viscous or ropy texture
⬩ Discoloration
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7. 7
S.
N
Milk Product Defect Microorganisms
1
Pasteurized
Milk
Rancid Peudomonas, Alkaligenes,
Staphylococcus
Ropy or Slimy Pseudomonas, Alkaligenes,
Coliforms, Bacillus Subtilis
Sour Lactic acid Bacteria
Bitter or Fruity Peudomonas, Alkaligenes,
Proteus, Flavobacterium
Discoloration Chromobacterium

8. 8
S.
N
Milk Product Defect Microorganisms
2. Creamed Milk
Swelling, Gas Clostridium, Sporogenes
3. Cream
Foamy Candida, Torulopsis
4. Butter
Surface taint Pseudomonas, Alteromonas

9. 9
S.
N
Milk Product Defect Microorganisms
5 Cheese
Gassy, Butyric acid Clostridium tyrobutyrcium
Moldy Penicillium, Scopulariopsis,
Mucor
Gassy Floating or
split curd
Leuconostoc, Streptococcus lactic
6 Soft Cheese
Black mold Mucor
Surface growth Torulopsis,
Debaryomyces

10. 10
S.
N
Milk Product Defect Microorganisms
7. Yoghurt
Yeasty Yeast (Torulopsis)

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