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