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Microbes - Friend or Foe 1
Microbes - Friend or Foe
Dairy Products
Microbes - Friend or Foe 2
Potential Pathogens in Milk
• Listeria
• Salmonella
• E. coli
• Campylobacter
• Yersinia
• Staphylococcus aureus
• Clostridium
Microbes - Friend or Foe 3
Listeria monocytogenes
• Soil, dust, mud and animals
• Can multiply at refrigeration temperatures
• Can cause meningitis and septicaemia
Microbes - Friend or Foe 4
Salmonella
• Over 2000 types
• Cows, poultry, pigs
• Diarrhoea, cramps, vomiting and fever
Microbes - Friend or Foe 5
Escherichia coli
• Rare, infective dose 10 cells
• Faecal material into milk
• Abdominal pain and severe diarrhoea
Microbes - Friend or Foe 6
Clostridium perfringens
• Environment, human and animal intestines
• Ingestion of large numbers cause illness
• Cramps and diarrhoea
Microbes - Friend or Foe 7
Staphylococcus aureus
• Nose, throat and skin of healthy people
• Can cause food poisoning when ingested
• Abdominal pain and vomiting
Microbes - Friend or Foe 8
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
Microbes - Friend or Foe 9
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 10
Hand swabs
Microbes - Friend or Foe 11
Raw Milk Quality
Microbes - Friend or Foe 12
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 13
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
Microbes - Friend or Foe 14
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 15
Raw Milk Quality
• No added water
• No antibiotic residues – Starter cultures
• No taints
• Good compositional quality
Microbes - Friend or Foe 16
Typical Milk CompositionFat 4%
Protein 3.5%
Lactose(Milk Sugar)
5%
Vitamins/Minerals
0.5%
Water 87%
Microbes - Friend or Foe 17
Other Dairy ProductsSkimmed 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 18
Summary so far
• Pathogens
• Source
• Effect
• Milk quality
• How do we eliminate any pathogens in raw milk?
Microbes - Friend or Foe 19
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 20
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
Microbes - Friend or Foe 21
Friendly Microbes
• Milk to vats
• Starter cultures added
Bacteria
Lactose Lactic Acid
Microbes - Friend or Foe 22
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 23
Lactococcus lactis ssp cremoris
Microbes - Friend or Foe 24
Bacteria in Yogurt
• Lactobacillus bulgaricus
• Streptococcus thermophilus
• Lactobacillus acidophilus
• Bifidobacterium
Microbes - Friend or Foe 25
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
Microbes - Friend or Foe 26
Other effects of Bacteria
• Produce gases – Edam
• Produce flavour and aroma
• Produce enzymes
Microbes - Friend or Foe 27
Other Microbes in Cheese
• Moulds: Penicillium camembertii Penicillium roquefortii
• Added to affect flavours
• Others: MicrococcusYeasts
Moulds
Microbes - Friend or Foe 28
Blue Stilton Production
• 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 29
Blue Stilton Production
• 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 30
Blue Stilton Production
• 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 31
Summary
• Potential pathogens in milk
• Source, effect and prevention
• Testing of raw milk quality
• Pasteurisation
• Friendly bacteria
• Blue stilton production