Microbes - Friend or Foe
Dairy Products
Microbes - Friend or Foe
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Potential Pathogens in Milk
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Listeria
Salmonella
E. coli
Campylobacter
Yersinia
Staphylococcus aureus
Clostridium
Microbes - Friend or Foe
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Listeria monocytogenes
• Soil, dust, mud and
animals
• Can multiply at
refrigeration
temperatures
• Can cause meningitis
and septicaemia
Microbes - Friend or Foe
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Salmonella
• Over 2000 types
• Cows, poultry, pigs
• Diarrhoea, cramps,
vomiting and fever
Microbes - Friend or Foe
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Escherichia coli
• Rare, infective dose 10
cells
• Faecal material into
milk
• Abdominal pain and
severe diarrhoea
Microbes - Friend or Foe
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Clostridium perfringens
• Environment, human
and animal intestines
• Ingestion of large
numbers cause illness
• Cramps and diarrhoea
Microbes - Friend or Foe
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Staphylococcus aureus
• Nose, throat and skin
of healthy people
• Can cause food
poisoning when
ingested
• Abdominal pain and
vomiting
Microbes - Friend or Foe
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Source of potential pathogens
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The cow – coat, udders, faecal contamination
Environmental - Soil, bedding, food
Mastitis
Milk handling equipment
Producer
Prolonged holding of milk in silo
Mixing old and new milk
Microbes - Friend or Foe
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Hygiene procedures
• Daily cleaning of milking apparatus
• Farmer washing hands / wearing gloves
• Not milking cows with mastitis
• Not feeding hay/ silage while milking
Microbes - Friend or Foe
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Hand swabs
Microbes - Friend or Foe
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Raw Milk Quality
Microbes - Friend or Foe
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Temperature
• Tested on arrival
• Below 5ºC
• Organisms and
temperature influence
bacterial proliferation
Number of bacteria per ml
after 24 hours
5ºC
2,600
10ºC
11,600
12.5ºC
18,800
15.5ºC
180,000
20ºC
450,000
Microbes - Friend or Foe
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Animal cell counts
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Test for low level of animal cells
Epithelial cells and white blood cells
Mastitis
High level indicates sub clinical mastitis
Pathogens Streptococcus & S. Aureus
Microbes - Friend or Foe
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Low levels of bacteria
• Resazurin test
• Changes colour by actively proliferating
bacteria
• Blue, Lilac = Low level of bacteria
• Pink, white = High level - Retest
Microbes - Friend or Foe
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Raw Milk Quality
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No added water
No antibiotic residues – Starter cultures
No taints
Good compositional quality
Microbes - Friend or Foe
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Typical Milk Composition
Fat
4%
Protein
3.5%
Lactose
(Milk Sugar)
Vitamins/
Minerals
Water
5%
0.5%
87%
Microbes - Friend or Foe
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Other Dairy Products
Skimmed Milk
<0.5% Fat
Cream
18 – 48% Fat
Butter
80% Fat
Yogurt
0 – 10% Fat
Cheese
(Full Fat)
30 – 35% Fat
Microbes - Friend or Foe
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Summary so far
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Pathogens
Source
Effect
Milk quality
• How do we eliminate any pathogens in raw
milk?
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Pasteurisation
• Discovered by Louis Pasteur
• Milk is heated to 72oC for at least 15
seconds.
• Cooled immediately.
• Pasteurisation kills harmful bacteria
(Pathogens).
• Mycobacterium paratuberculosis.
Microbes - Friend or Foe
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Phosphatase test
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To test pasteurisation process efficacy
To check no raw milk contamination
Phosphatase is an enzyme
Inactivated by pasteurisation
Any remaining phosphatase activity =
pasteurisation process not effective
Microbes - Friend or Foe
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Friendly Microbes
• Milk to vats
• Starter cultures added
Bacteria
Lactose
Lactic Acid
Microbes - Friend or Foe
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Examples of Starter cultures
Blue stilton
• Lactobacillus lactis subsp diacetylactis
• Leuconostoc mesenteroides subsp cremoris
White stilton
• Lactobacillus lactis subsp lactis
• Lactobacillus lactis subsp cremoris
Microbes - Friend or Foe
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Lactococcus lactis ssp cremoris
Microbes - Friend or Foe
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Bacteria in Yogurt
• Lactobacillus bulgaricus
• Streptococcus thermophilus
• Lactobacillus acidophilus
• Bifidobacterium
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Why do we need friendly bacteria?
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Acidification of cheese by starter bacteria
Results in optimum lactic acid content
Allows protein coagulation by rennet = curd
Stir and Cut the curd – release whey
Fat retained in the coagulum
Water drains out in the whey
Microbes - Friend or Foe
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Other effects of Bacteria
• Produce gases – Edam
• Produce flavour and aroma
• Produce enzymes
Microbes - Friend or Foe
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Other Microbes in Cheese
• Moulds: Penicillium camembertii
Penicillium roquefortii
• Added to affect flavours
• Others: Micrococcus
Yeasts
Moulds
Microbes - Friend or Foe
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Blue Stilton Production
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Raw Milk
(5°C)
Fat adjustment (Standardisation)
Pasteurisation
(72°C, >15 secs)
Transfer to Vat
(30°C)
Add Starter Culture (Bacteria)
Add Blue Mould
Add Rennet (To coagulate protein)
Microbes - Friend or Foe
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Blue Stilton Production
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Acid development and curd formation
Drain whey off curd
Salt and mill curd
Fill hoops
Drainage
(20°C)
Cool, de-hoop and cling film (10°C)
Remove cling film
Microbes - Friend or Foe
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Blue Stilton Production
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Maturation
(13°C)
Skewering
(To allow air in)
Further maturation
(13°C)
Transfer to cold store
(5°C)
Cutting & Wrapping / Packing
Microbes - Friend or Foe
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Summary
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Potential pathogens in milk
Source, effect and prevention
Testing of raw milk quality
Pasteurisation
Friendly bacteria
Blue stilton production
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