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Food Microbiology 1 Unit 10 Microbiology of Food Groups II

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Food Microbiology 1 Unit 10 Microbiology of Food Groups II Food Microbiology 1 Food Groups Meat and Poultry Eggs Fish and other Seafood Milk and Dairy Products ... – PowerPoint PPT presentation

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Title: Food Microbiology 1 Unit 10 Microbiology of Food Groups II


1
Food Microbiology 1
Unit 10 Microbiology of Food Groups II
2
Food Groups
  • Meat and Poultry
  • Eggs
  • Fish and other Seafood
  • Milk and Dairy Products
  • Vegetables
  • Baked Products

3
Fish and Other Seafood
4
Fish
  • Microorganisms in fish depend on
  • Temperature
  • Season
  • Marine or fresh water
  • Post-harvest handling (ice)
  • pH of fish gt 6

5
  • High level of free amino acids but no
    carbohydrates
  • Amino acid metabolism produces ammonia and
    hydrogen sulfide
  • Main spoilage bacteria
  • Pseudomonas spp.

6
Pathogenic Bacteria
  • Vibrio paraheamolyticus (water borne)
  • Listeria monocytogenes (post-harvest
    contamination)
  • Bacillus and Clostridium spp.
  • Canned tuna was associated with an outbreak of
    botulism in the 1980s

7
Other Seafood
  • Oysters (shellfish)
  • Act like filters for the water and they can
    accumulate contamination
  • Major pathogenic contaminants are enteric
    viruses and waterborne pathogens
  • E.g. vibrio vulnificus

8
Milk and Dairy Products
9
Milk and Dairy Products
  • Raw Milk
  • Pathogens associated
  • E. coli O157H7
  • Salmonella typhimurium
  • Campylobacter jejuni
  • Listeria monocytogenes
  • Staphylococcus aureus (mastitis)

10
Why is raw milk consumed?
  • Easy access to raw but less access to
    pasteurized
  • Drinking raw milk has been practiced over time
  • A notion that raw milk is better than pasteurized


11
Spoilage bacteria
  • Bacteria that limits the shelf life
  • Total Psychrotrophic counts in raw milk
  • Needs to be lt100,000 cfu/ml single farm or
    300,000 cfu/ml combined farms
  • Psychrotrophic spore formers
  • Bacilus cereus
  • Lipolytic and proteolytic psychrotrophs
  • Pseudomonas fluorescens
  • Release heat resistant enzymes

12
Post-Pasteurization Contamination
  • Pseudomonas spp.
  • Bacillus cereus
  • Lactic acid bacteria

13
Standards for Pasteurized Milk and Milk Products
  • Temperature cooled to 10oC or less
  • Bacterial counts lt 20, 000 cfu/ml
  • Coliform counts lt 10 cfu/ml
  • Antibiotic presence negative
  • Phosphatase lt 1?g

14
Dried Milk
  • Low water activity prevents growth of pathogens
    and spoilage bacteria
  • Largest foodborne illness outbreak associated
    with Staphylococcus aureus was in Japan 2000,
    13,000 cases
  • The incident was the result of
    post-pasteurization contamination with Staph
    aureus toxin that is not destroyed by drying

15
Fermented milk products produced by bacterial or
fungal transformation for carbohydrate
(lactose-lactate)
  • Fermented products are preserved by acids and
    alcohol produced by the beneficial bacteria that
    inhibits spoilage bacteria and pathogens

16
Cheese
  • Product made from the curd of the milk of cows
    or other animals
  • Casein coagulated by rennin and acid
  • Subsequent heating, salting, pressing, aging

17
Cheese
Classified into 1- Soft unripened cream
cheese 2- Soft ripened (neutral pH, high aw)
Camembert 3- Semisoft Blue cheese 4- Hard (low
pH, low aw) Cheddar, Swiss 5- Very Hard
Parmesan
18
Pathogens in Cheeses
Mainly Soft cheeses. E.g. Brie
  • Listeria monocytogenes
  • E. coli O157H7
  • Salmonella
  • Brucella

19

Yoghurt
  • Prepared by adding starter cultures to milk at
    0.1-2 w/v
  • Starter cultures used
  • Streptococcus thermophilius
  • Lactobacillus bulgaricus
  • Lactic Acid formed results in a final product pH
    of 4.4-4.6
  • Acetaldehydes responsible for flavor and aroma
    of the product

20
Yoghurt
Symbiotic Growth
Streptococcus produces formic acid to stimulate
Lactobacillus
Lactobacillus
Streptococcus
Lactobacillus breaks down proteins to peptides
and amino acids stimulating growth of
Streptococcus
21
Yoghurt
  • Low pH inhibits pathogens
  • An outbreak in the UK in 1997 with Clostridium
    botulinum when hazelnut conserve was added to
    yoghurt. 27 cases of botulism
  • Spoilage can occur as a result of contamination
    at pre-fermentation
  • Yeasts and molds
  • Heterofermentative lactic acid bacteria
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