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Food Microbiology > Biological Methods of Preservation > Flashcards

Biological Methods of Preservation Flashcards

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1
Q

Define Biopreservation:

Give some examples:

A

Use of Microorganisms, their metabolic products, or both to preserve food (excluding fermentation)

  • controlled acidification
  • bacteriocins
  • bacteriophages
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2
Q

What is controlled acidification?

A

acidification of food for preservation:

done by direct addition of organic acid, fermentation, or use LAB to produce in situ

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3
Q

What is MicroGard?

A

form of controlled acidification:
contains fermentable carb + customized culture (depending on product)
acts as safeguard: if food temperature abused -> MicroGard microbes will grow and make acid, prevent pathogens

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4
Q

What are the main benefits of MicroGard?

A
  1. protect shelf life/safety
  2. maintain organoleptic qualities
  3. “natural” product
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5
Q

What is the Winsconsin process, and what are the advantages?

A

add less nitrite, 0.7% sucrose, LAB: to prevent C. botulinum in bacon

less nitrite needed (less potential carcinogens)

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6
Q

What are bacteriocins?

Bacteriocins produced by ____ are of particular interest.

A

antimicrobial peptides produced by bacteria that are lethal to others, but not the producer (or humans)

LAB

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7
Q

What are the different categories of bacteriocins?

A

Class I, Class II, Class III, Class IV

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8
Q

What are the Class I bacteriocins and how are they made?

A

unusual AA; made by posttranslational modification

ex: dehydroalanine, dehydrobutyrine, lanthionine, methyllanthione

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9
Q

What is a specific subcategory of Class I bacteriocins? How is it produced?

A

Lantibiotics (containing lanthionine ring)

rxn of dehydro-amino acids with cysteine -> thioether lanthionine

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10
Q

What is the best characterized LAB bacteriocin? What category does it belong in, and how is it produced industrially?

A 
NISIN
class I bacteriocin

made by culturing L. lactis (not synthesized chemically) -> for cheese/meat/beverages

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11
Q

True/False: Nisin is produced by lactic acid bacteria

A

True

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12
Q

What is an example of a lantibiotic not made by LAB? What is it used for?

A

subtilin (made by Bacillus subtilis)

antibacterial action; also protease (food, laundry detergent, lens cleaners)

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13
Q

What are 2 examples of lantibiotics?

A

subtilin, nisin

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14
Q

What are class II bacteriocins?

A

small heat stable proteins

with consensus leader sequence that signals to cell to export protein

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15
Q

What are the subclasses of Class II bacteriocins?

A

IIa: active against L. monocytogenes
IIb: requires 2 different peptides for activity
IIc: requires reduced cysteine for activity

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16
Q

What are class III bacteriocins?

A

> 30kDa (large) heat-liable proteins

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17
Q

What are class IV bacteriocins?

A

with lipid or carb components (unknown function)

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18
Q

What method is used to discover new bacteriocins?

A

Place colony of bacteriocin producer onto agar inoculated with lawn of other bacterium -> incubate, observe for ZONE OF INHIBITION (circle of no growth)

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19
Q

True/False: a zone of inhibition indicates there is definitely bacteriocin production

A

False: could be other inhibitory substance (organic acid, H peroxide, phage contamination)

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20
Q

How can you differentiate between the potential causes of a zone of inhibition?

A

bacteriocin: sharp edges, colony in center
organic acid: fuzzy edges
Phage: no colony n center

Perform test: remove colony, apply protease -> if it was bacteriocin, then the bacteria should now be able to grow over

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21
Q

What is the general mechanism of all LAB bacteriocins?

A

disrupt integrity of cytoplasmic membrane

  1. bind and create pore (hole)
    or
  2. membrane solubilization
22
Q

Bacteriocins are most effects against cells in what state?

A

vegetative

23
Q

What is the effect of bacteriocins on vegetative cells?

A

disrupt membrane -> ions, AA, ATP will spill out -> ruins chemical/electrical gradient -> cannot generate energy, cannot protect from outer environment -> inhibition or death

24
Q

What property of bacteriocins allows for its effects against the membrane?

A

amphiphilic cationic peptides -> can insert into membrane

25
Q

True/False: Nisin will encourage germination of spores, making it risky to use as a bacteriocin

A

False: it DOES encourage germination, BUT: will attack pre-emergent spore (before starts growing)
(germinated spore is more vulnerable than dormant)

26
Q

What are Colicins?

A

bacteriocins made by some strains of E. coli against other strains

27
Q

What do E. coli strains need to be able to produce colicin?

A

colicinogenic plasmic

genetic info for synthesis, immunity, and release

28
Q

Colicin expression is under the ____ regulatory system

A

SOS

29
Q

Describe the mechanism of action for colicin:

A

binds to specific receptors (outer membrane proteins for nutrient uptake) -> enter, transported by Tol or TonB -> disrupt inner membrane or attack DNA, rRNA, or tRNA

30
Q

True/False: colicin must enter the bacterial cell in order to be lethal

A

true (attacks inner mechanisms)

31
Q

The 2 classes of colicins:

A

enzymatic

pore-forming

32
Q

What are the lethal modes of action of enzymatic colicins?

A
  1. block synth of peptidoglycans
  2. cleave tRNA -> stop protein synth
  3. cleave 16S rRNA -> stop protein synth
  4. DNA degradation
33
Q

What are the approved ways to add bacteriocins to food?

A
  1. add purified bacteriocin directly
  2. add producing culture (make in situ)
  3. choose bacteriocin making culture to include for fermentation
34
Q

Give an example of a bacteriocin that is added to food:

What are its main purposes?

A

Nisin: for milk, cheese, dairy, canned food, smoked fish, mayo, baby food (GRAS)

anti-listerial agent; sensitize spores to heat (prevent botulism, lessen thermal treatment time needed)

35
Q

Is Nisin used alone or in conjunction with other treatments?

A

Together - part of a multiple barrier inhibitory system

ex: with mod. atmosphere storage (fresh fish, ground pork)

36
Q

What is a bacteriocin that is produced in situ in food? What does it protect against?

A

Pediocins (in wieners, dressings, cottage cheese, meat, RTE salad)

effective against vegetative L. monocytogenes (not good for spores)

37
Q

The protective effect of pediocin is more effective with (higher/lower) temperatures, and better in (aerobic/anaerobic) conditions

A

lower

anaerobic

38
Q

Why is a bacteriocin producing strain beneficial for the making of fermented foods? Give an example

A

helps inactivate existing bacteria -> allow for culture to grow, better chance of success

ex: adding pediocin producers to sausage -> reduces L. monocytogenes

39
Q

how does bacteriocin producers affect shelf life in fermented foods? give an example:

A

Increase shelf life

ex: add nisin producing LAB to cheese -> shelf life increased from 14 to 87 days

40
Q

True/False: unlike antibiotics, bacterial resistance is not a concern with bacteriocins.

A

False: resistant strains exist and can develop!

41
Q

What are some developed resistance mechanisms to bacteriocins that have been observed? How does specificity vary?

A
  1. destruction of bacteriocin (specific or general)
  2. modification (specific)
  3. Altered receptors (specific)
  4. Membrane composition (general)
42
Q

Can bacteriocin resistance be overcome by applying a combo of different bacteriocins? Why or why not?

A

Yes, if it is a specific resistance mechanism

No, if it is a general mechanism (need a different functioning bacteriocin)

43
Q

Is cross-resistance with antibiotics an issue for bacteriocin resistance?

A

Usually no;

Multidrug resistant bacteria can still be sensitive to bacteriocin

44
Q

What is a resistance mechanism observed in L. monocytogenes against nisin?

A

modified membrane composition - more straight chain FA (less fluidity) -> nisin can’t insert as easily

45
Q

What is a specific defense mechanism against dehydroreductase bacteriocins?

A

Modification

46
Q

What is important in the food industry to combat bacteriocin resistance?

A

Apply multiple hurdle technology (use many diff steps/methods to kill bacteria)
Bacteriocin resistant cells can be sensitive to other factors (heat, cold, etc)

47
Q

True/False; we normally consume bacteriophages

A

True (part of natural food microbiota)

48
Q

What are the main challenges with using phages for microbial control in food?

A
  1. lack of consumer acceptance
  2. possible resistance
  3. low numbers of bacteria in food (phage cannot effectively grow)
  4. targets specific species/strain
49
Q

Phages need _____ actively growing bacteria to be effective

A

10^5 - 10^6

50
Q

There are commercial phages used to control growth of ___, ___ and ____.

A

Salmonella, E. coli, Listeria

51
Q

How is bacteriophage resistance created? How can we overcome this?

A

changes in bacteriophage receptor site (proteins, LPS, lipoproteins on surface)

use mix of different phages (if one is useless, other still are functional)

Food Microbiology (21 decks)

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