Summary Advanced food microbiology

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Summary - Advanced food microbiology

  • 1 Microbiological Food Safety

  • What does this formula stand fore?
    Number of cases of type i (phage and sero-types) in food j:

    M(j): Mass food product
    p(ij): prevalence of microorganism in food product (how many times pressent)
    q(i): type food (infectivity/survivablility) of the microorganism 
    a(j): survival/growth, is it eaten raw or cooked
  • Why is there almost no salmonella on eggs but has it a lot of deaths?
    Because it is eaten raw, there is no further processing and therefore the salmonella is not inactivated.
  • What are the prerequisites for safe food?
    Basic/common sense
    GMP (good manufacturing practice), GHP (good hygienic practice) and GLP (good laboratory practice)
  • What are the seven steps in HACCP?
    1. Hazerds
    2. CCPs
    3. limits 
    4. monitor
    5. corrective actions
    6. verification
    7. documentation
  • What is QRA and what part of the HACCP does it contain and how are they determont?
    Quantitative risk assessment, 
    1. hazards
    2. CCPs
    3. limits

    Can be determont globaly, specific or extensive. 
    And can be set by authorities
  • For what part of the HACCP is ISO and certification?
    ISO:international organization for standardization

    Is used for:
    5. corrective action
    6. verification
    7. documentation
  • What does this formula stand fore
    H(0): initional microorganisms pressent

    ∑R: some of reduction (washing, heating)

    ∑G: growth 

    ∑C: contamination
     FSO: food safety objective (cfu/g or prevalence)
  • What is this picture?
    This picture is the norm set by fovernement.
    The some of H0 and R shoud be bigger then G and C. in order to abtian the Food safety objectives.
  • What does ALOP stand for?
    Appropriate Level of Protection
    illnesses/year

    D/R, consumption, ethics, “distribution” of product groups
  • What does FSO stand for?
    FSO Food Safety Objective
    cfu/g or prevalence (%) at consumption

    “distribution” over the chain
  • What does PO stand for?
    Performance Objective
    cfu/g or prevalence (%)

    “distribution” over phenomena (initial contamination, growth, inactivation, recontamination)    

    Limit witch industry should stay under
  • What is the difference between PO and FSO?
    PO: performance objective. 
    The limit which the industry should stay under.
    So growth and inactivation due to processing with the consumer still has to be taken into account.

    FSO: Food Safety Objective
    The limit which the food product with the consumer should stay under.
    Does take into account growth and inactivation.
  • What does PC stand for?
    Performance Criterion
    >6D inactivation, <3 logs growth

    quantitative microbiology, experiments, literature
    Process criterion 15s 71.5°C
    Product criterion pH<4.6
  • What does this formula stand for?
    rc:
    C(air): concentration in air
    V(s): speed movement,
    A: surface
    t: time
  • 2 Minimal processing of Foods

  • What is UHP/HHP?
    Ultra high pressure processing. 
    High hydrostatic pressure

    A lot of force is put on one point., over 75 MPa
  • Why does UHP/HHP work?
    The membrane of the microorganism is damaged and therefore the cell dies. Since a cell can not live without the processes happening in the cell.
  • How does the inactivation by HHP go over time and aw-value?
    The lower the water activity the more time is needed in order to inactivate the microorganisms.
  • At what pressures do spores become inactivated?
    1000 MPa
  • What is the effect of HHP on inactivation of spores?
    The higher pressure the more spores inactivated but also depends on the type of spore bacteria. 

    Copnclusion spores can survive high pressure treatment
  • What is (PEF) processing?
    Puls electric field processing. 
    The membrane of the microorganism breaks because:
    20-60 kV/cm goes trough it.

    The balance between + outside the cell and - inside the cell is disturbed and therefore holes are present in the cells. Therefore there is a dis-balance of compounds in and outside the cell and it will die. 

    However you do need a wet product like dairy, soup, sauces, fruit juices.
  • How is the effectivety of PEF processing influanced?
    Type of patogen and pH. 

    The higher the pH the better the inactivation by PEF.
  • What are bacteriophages?
    These are viruses specific for micro-organisms.

    • Obligate parasites 
    • Found everywhere  
    • Diversity in shapes and forms 
    • Narrow host range 
    • Affect performance of their host  
  • What is the lytic cycle of a virus?
    This is the unpatient cycle. 
    The virus enters the cell. Starts replicating itself and and advantualy the cell will burst open and the virus will be spread.
  • What is the lytogenic cycle of a virus?
    The unpatient cycle. 
    The DNA of the virus is build in the DNA of the micro-organism and also replicates when the cell is replicating. At a certain point one replication will due to a certain factor extreete the virus its DNA and now it can work as the same as the lytic cycle.
  • What is the holin-lysin module?
    The two proteins that allows the viruses produced in the cell to leave the host cell. 

    The holin makes a hole in the membrane.
    The lysin goes trough the holin and will break the cell wall. 
    Because there are a lot of components in the cell wall there are a lot of different lysins.
  • What are the two functional domains of a lysin?
    One part is the cell binding domain: this will give specificity to the lysin and only binds to a certian part of the cell wall. 

    The other part is the catalytic domain: this will give the activity to the lysin. So this catalyses the break down of the cell wall.
  • Why do you usually need a mix of baterio phages?
    You need a mix because they are super specific and they will only deactivate on type of listeria for instance, To deactivate more you will need a mix.
  • What can you do if people don't want to add bactero phages.
    Just add the lysin because it will degrade the cell wall.
  • What can influance the activity of lysins?
    The type of food sins the lysins might bind to different things in the food.
  • How can fermentation improve food safety?
    This might be because acids are produced and the other organism can not stand this.
    Or there is competition and the fermenting organism wins form the pathogen.  
    But most important antimicrobial peptides.  
  • What are antimicrobial peptides?
    Peptides produced by a specific micro-organism that will kill other micro-organisms by damaging the cell wall.
    The producing micro-organism has an immunity mechanism for this peptide. 
    Very effective since it can work in the nM range.
  • What is the disadvantage of antimicrobial peptides?
    They are very specific and they might work in the lab but not in food because many other components are present.
  • What is nisin?
    A commonly used anti-microbial peptide.
    It attacks listeria.
  • Why does antimicrobial peptides only work on grampositive bacteria?
    This is because it works on the cell wall and the gram positive cell wall is easier to reach then the one of the gram negative cell wall. The - has two cell walls so the real cell wall is harder to reach.
  • What does a hurdle technique mean?
    applying a combination of preservation methods.
    Hurdle technology deliberately combines existing and new preservation techniques to establish a series of preservative factors (hurdles) that the microorganisms in question are unable to overcome (jump over). These hurdles may be temperature, water activity, acidity, redox potential, preservatives, and others.
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What is very specific about the definition of prebiotics?
It is a component or ingredient. 
So no living organism.
It has to be fermented in the colon.

Independent on bacterial group/species
Health effect
What is the ideal niche for moulds?
One with a low Aw and a high sugar content.
What is c and n for case 10 till 15?
See picture
What is c and n for case 4 till 9?
See picture
As a product developer, which two bacteria would you choose for your new probiotic product?
  • lactobacillus acodophilus
  • lactobacillus casei 
What are two disadvantages of probiotics
  1. The positive effects are only temporarily.
  2. The number of food products is restricted because of the requirement to use living cells.
he number of which bacterium, present in the large intestine, varies a lot between people?
Lactobacillus
What is essential in factories, besides regular cleaning and disinfection, to prevent biofilm formation?
Good facterial and hygenic disign
Which three methods can be used for enumeration of bacteria in products?Spiral platerPCRELISAChromogenic mediaTEMPO

Spiral plate
Chromogenic media
TEMPO
What does a hurdle technique mean?
applying a combination of preservation methods.
Hurdle technology deliberately combines existing and new preservation techniques to establish a series of preservative factors (hurdles) that the microorganisms in question are unable to overcome (jump over). These hurdles may be temperature, water activity, acidity, redox potential, preservatives, and others.