Food Microbiology 1

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Food Microbiology 1
Unit 10 Microbiology of Food Groups
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Food Groups

• Meat and Poultry
• Eggs
• Fish and other Seafood
• Milk and Dairy Products
• Vegetables
• Baked Products

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Meat and Poultry
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Meat and Poultry

• Cattle
• Pigs
• Sheep
• Poultry

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Main Pathogens of Concern

• E coli O157 H7 (cattle)
• Salmonella (Poultry and eggs)
• Campylobacter jejuni (poultry and eggs)
• Listeria monocytogenes (pigs)
• Clostridium perfringens (soil borne)

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Spoilage Bacteria

• Aerobic
• Pseudomonas
• Acinetobacter
• Morexella

Protease activity leads to off odors and poor
texture
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Source of Contamination in Red Meat

• Primary Source of Contamination
• Feces
• Hide contact
• Aerosols and Sprays
• Contaminated hands and equipment
• Spilling of body fluids

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Example Cattle Slaughter
Cross-contamination of hide during transport and
holding
Cattle Receiving and Holding
Stunning
Contact with floor after stunning
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Carcass Post-Evisceration Decontamination

• USDA HACCP recommends a carcass decontamination
  (pasteurization) step
• Organic acid wash, lactic and/or acetic acid
• Hot water
• Steam pasteurization

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Carcass Decontamination

• Not totally effective at removing contamination
• Residual contamination can be spread during
  grinding
• Irradiation starting to be introduced

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Meat Products
Dried, Salted and/or Cured

• E.g. Salted pork, ham
• Water activity reduced by withdrawing water
• Suppress growth of majority of microbes

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Meat Products
Fermented Sausage

• E.g. Salami, pepperoni
• Products are fermented with starter bacterial
  cultures
• Addition of curing salts (e.g. nitrites), spices
  and sugar
• Emulsified then placed into casings
• Slow drying over 3 weeks to 8 months
• Hurdles (low aw, nitrites, and low pH)

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Meat Products
Cured, Cooked Meat Products

• E.g. Bologna Sausages
• Cured meat
• Packed into casings
• Heat treated
• Sliced and packed
• Hurdles (low aw, heat treatment, vacuum packing)
• Re-contaminated with Pseudomonas or lactic acid
  bacteria

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Meat Products
Cooked not Cured

• E.g. Pies
• Refrigerated or frozen
• Hurdles (Heating, cold temperature)
• Re-contamination with pathogens can cause
  problems
• Staphylococcus aureus
• E coli O157

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Eggs and Egg Products
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Egg and Egg products

• They are sterile when they are laid but the
  outer membranes and shells may be penetrated by
  bacteria after several hours

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Spoilage

• Proteus spp. Causes black rot in eggs and gives
  it the rotten odor
• Pseudomonas spp. Causes green rot caused by
  sideophore (iron-chelating) production

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Pathogens

• Salmonella enteritidis commonly associated with
  eggs
• Initially on the surface of eggs can penetrate
  shell
• During storage inner shell membrane weakens
  enabling Salmonella to reach yolk (nutrient
  source)

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• High risk foods
• Egg custard
• Soft boiled
• Fried sunny side-up
• Mayonnaise low pH restricts growth
• Pasteurized eggs are recommended for vulnerable
  groups

Lightly cooked so Salmonalla can survive