Dairy Products

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Microbes - Friend or Foe

• Dairy Products

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Potential Pathogens in Milk

• Listeria
• Salmonella
• E. coli
• Campylobacter
• Yersinia
• Staphylococcus aureus
• Clostridium

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Listeria monocytogenes

• Soil, dust, mud and animals
• Can multiply at refrigeration temperatures
• Can cause meningitis and septicaemia

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Salmonella

• Over 2000 types
• Cows, poultry, pigs
• Diarrhoea, cramps, vomiting and fever

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Escherichia coli

• Rare, infective dose 10 cells
• Faecal material into milk
• Abdominal pain and severe diarrhoea

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Clostridium perfringens

• Environment, human and animal intestines
• Ingestion of large numbers cause illness
• Cramps and diarrhoea

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Staphylococcus aureus

• Nose, throat and skin of healthy people
• Can cause food poisoning when ingested
• Abdominal pain and vomiting

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Source of potential pathogens

• 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

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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

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Hand swabs
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Raw Milk Quality
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Temperature

• Tested on arrival
• Below 5ºC
• Organisms and temperature influence bacterial
  proliferation

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Animal cell counts

• Test for low level of animal cells
• Epithelial cells and white blood cells
• Mastitis
• High level indicates sub clinical mastitis
• Pathogens Streptococcus S. Aureus

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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

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Raw Milk Quality

• No added water
• No antibiotic residues Starter cultures
• No taints
• Good compositional quality

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Typical Milk Composition
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Other Dairy Products
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Summary so far

• 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.

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Phosphatase test

• 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

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Friendly Microbes

• Milk to vats
• Starter cultures added
• Bacteria
• Lactose Lactic Acid

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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

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Lactococcus lactis ssp cremoris
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Bacteria in Yogurt

• Lactobacillus bulgaricus
• Streptococcus thermophilus
• Lactobacillus acidophilus
• Bifidobacterium

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Why do we need friendly bacteria?

• 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

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Other effects of Bacteria

• Produce gases Edam
• Produce flavour and aroma
• Produce enzymes

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Other Microbes in Cheese

• Moulds Penicillium camembertii Penicillium
  roquefortii
• Added to affect flavours
• Others Micrococcus Yeasts Moulds

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Blue Stilton Production

• Raw Milk (5C)
• Fat adjustment (Standardisation)
• Pasteurisation (72C, gt15 secs)
• Transfer to Vat (30C)
• Add Starter Culture (Bacteria)
• Add Blue Mould
• Add Rennet (To coagulate protein)

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Blue Stilton Production

• Acid development and curd formation
• Drain whey off curd
• Salt and mill curd
• Fill hoops
• Drainage (20C)
• Cool, de-hoop and cling film (10C)
• Remove cling film

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Blue Stilton Production

• Maturation (13C)
• Skewering (To allow air in)
• Further maturation (13C)
• Transfer to cold store (5C)
• Cutting Wrapping / Packing

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Summary

• Potential pathogens in milk
• Source, effect and prevention
• Testing of raw milk quality
• Pasteurisation
• Friendly bacteria
• Blue stilton production