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5) Food Microbiology > 2) Acetic Acid Bacteria > Flashcards

2) Acetic Acid Bacteria Flashcards

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1
Q

what are general functions of fermenting food?

A
  • improves organoleptic profile of food material
  • extends shelf life
  • improves availability of nutrients
  • develops some health promoting properties
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2
Q

what are 3 ways to start a fermentation rxn?

A
  1. spontaneous fermentation
  2. inoculated fermentation
  3. back sloping
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3
Q

describe spontaneous fermentation

whats an example?

A

based on action of wild microorganisms already naturally on the food or in the area
 can encourage growth of certain microbes by creating optimal condition
- eg. sauerkraut

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4
Q

describe inoculated fermentation

example?

A

based on introducing a single (pure culture) or several (mixed culture) into an environment that favors their proliferation
advantage: stabilizes fermentations sensitive to contamination
eg. wine

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5
Q

describe back slopping

example?

A

based on adding the product of a previously successful fermentation rxn to start a new rxn
eg. kombucha

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6
Q

what does AAB fermentations produce?

A

acetic acid products

such as kombucha or apple cider vinegar

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7
Q

what does AAB require?

A

alcohol and O2

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8
Q

what is the LAB fermentation rxn?

A

bacteria feeding on sugar –> produces lactic acid

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9
Q

what is the most common type of fermentation?

A

LAB

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10
Q

differentiate the use of starter cultures for vegetable vs dairy fermentations

A

veg: don’t need a starter culture, just good conditions for growth
dairy: requires starter cultures b/c it’s hard for LAB to overcome other bacteria in the mix

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11
Q

what are the 5 types of fermentation?

A
  1. AAB
  2. LAB
  3. alcoholic
  4. amylolytic
  5. proteolytic
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12
Q

describe amylolytic fermentations

A
  1. molds simplifies starches into simple sugars

2. simple sugars are used in secondary fermentation to produce alcohol

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13
Q

what is an example of amylolytic fermentations

A

koji and nuruk

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14
Q

what does amylolytic fermentations use?

A

molds (Aspergillus oryzae)

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15
Q

describe proteolytic fermentation

what are examples?

A
  • uses molds on high protein foods
  • uses a starter culture
  • tempeh (fermented soybean) and cheese (penicillium growth on rinds)
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16
Q

what are other names for acetic acid?

A

AcOH
ethanolic acid
vinegar
CH3CO2H

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17
Q

what do acidic properties of AcOH come from?

A

from H+ being able to separate from the rest of the molecule by ionization

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18
Q

what are ways that AAB can be produced?

A

synthetically

bacterial fermentation

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19
Q

is AAB gram pos or neg?

A

Gram-neg

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20
Q

what is the most commonly used AAB?

A

acetobacter sp

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21
Q

are AAB anaerobic or aerobic?

except what type of AAB?

A

aerobic

except acetogenic bacteria

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22
Q

what are acetogenic bacteria?

what do they produce?

what do they require?

A

type of AAB that produces AcOH anaerobically

requires one C compound and H

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23
Q

what can acetogenic bacteria NOT tolerate?

A

accumulating acetic acid

24
Q

why are acetogenic bacteria slower than oxidative AAB?

A

b/c they can’t tolerate accumulating AcOH, in comparison to oxidative AAB which are very tolerant

25
Q

what kind of environment does AAB live in?

A

high conc of sugar, alcohols or sugar alcohols

26
Q

what are sugar alcohols?

A

organic compounds derived from sugars and comprise a class of polyols

27
Q

what are sugar alcohols used in the food industry as?

A

thickeners and sweeteners

common for diabetics

28
Q

what are common sugar alcohols?

A

glycerol
xylitol
mannitol
sorbitol

29
Q

compare sucrose to sugar alcohols

A
  • sugar alcohols affect blood sugar levels, but less than sucrose
  • sugar alcohols have fewer calories
30
Q

what 2 enzymes are imp in converting EtOH to AcOH in the periplasm?

A

ADH: alcohol dehydrogenase

ALDH: aldehyde dehydrogenase

31
Q

in the periplasm, what AAB rxn occurs?

A
  1. AAB oxidizes EtOH to acetaldehyde (by ADH; coupled with UQ to UQH2)
  2. ALDH converts Acetaldehyde to ACOH
32
Q

what is overoxidation

A
  • occurs when strains oxidizes AcOH
  • causes H to be much lower (3.5) than the pH optimum for oxidation of organic acids (6.0)
  • causes production of Co2 and off flavours
33
Q

what is the pH optimum for oxidation of organic acids?

what is the pH that occurs with overoxidation?

A
  1. 0

3. 5

34
Q

what are the 2 phases of growth in overoxidation?

A
  1. first log phase: due to oxidation of ethanol to acetic acid
  2. second overoxidation phase: uses acetic acid as energy via TCA. Results in decreasing AcOH conc outside the cell
35
Q

what are two methods of AAB fermentations?

A
  1. surface stations processes

2. submerged processes

36
Q

describe surface stations process

A
  • one method of acetic acid fermentation
  • uses acetobacter
  • final conc of acid can reach 8-9%
  • AAB forms thin film on surface of growth media (containing the bacteria/mother of vinegar), which becomes thicker and more gelatinous with time.
37
Q

describe submerged process

A
  • method of AAB ferm
  • uses Komagateibacter strains
  • final conc of acid: 15-20%
  • involves rapid mixing with forced aeration in a bioreactor
38
Q

describe the toxic effects of AcOH

A

AcOH is a weak lipophilic acid that can diffuse through the cytoplasmic membrane and has a toxic effect on bacteria

toxic effect is b/c of dissociation of proton caused by higher pH of the cytoplasm –> internal pH in cytoplasm decreases –> uncoupling of oxidative phosphorylation –> disruption of proton gradient –> cell poisoning

39
Q

what are 4 primary mechanisms responsible for AAB resistance to acetic acid

A

 1. prevention of acetic acid influx into cells (CPS, EPS and LPS)
 2. acetic acid assimilation (overoxidation)
 3. acetic acid efflux (efflux pumps)
 4. protection of cytoplasmic proteins against denaturing (general stress proteins)

40
Q

what are molecular chaperones used for?

A

to deal with stress due to ethanol and acetic acid

41
Q

what are 2 categories of molecular chaperones?

A
  1. those involved in the restoration of denatured/aggregate proteins
  2. those involved in the degradation of denatured/aggregate proteins
42
Q

what are 3 functions of molecular chaperones?

A
  1. prevent denatured proteins from aggregating
  2. re-solubilize aggregated proteins
  3. facilitate degradation of very damaged proteins
43
Q

what is GroES-GroEL? what is its function?

A

chaperone that is representative of heat-shock proteins found in all bacteria

44
Q

describe the mechanism of GroES-GroEL

A

GroEL forms a heptamer ring structure; GroES forms a heptamer lid-like structure. Together they create the “central cavity”, where denatured proteins are separated from the outside, to allow them to safely re-fold into proper conformations

45
Q

when is GroES-GroEL expressed?

A

when AAB is suddenly exposed to ethanol or acetic acid.

46
Q

what is DnaK-DnaJ-GrpE?

what functions does it have?

A

chaperone

 folding nascent proteins
 refolding denatured proteins
 degrading very denatured proteins

47
Q

what is the expression of DnaK-DnaJ-GrpE linked to?

A

ethanol, not acetic acid

48
Q

describe the mechanism of DnaK-DnaJ-GrpE

A
  • DnaJ binds to improperly folded protein and targets them to DnaK
  • DnaK places protein into a cleft (in it’s open conformation)
  • DnaJ binds to DnaK and promotes ATP hydrolysis
  • DnaK closes
  • substrate protein is tightly bound
  • while being held by DnaK, the protein can’t aggregate with other proteins (can be fatal for cell)
  • GrpE releases proteins from DnaK by removing ADP from it and providing an ATP
49
Q

what is Komagateibacter spp. used in?

A

submerged industrial vinegar production

50
Q

how does Komagateibacter spp. avoid build up of AcOH inside the cell?

A
  • efflux pumps: eliminates excess dissociated acetate and protons
  • synthesis of EPS (extracellular polymeric substance) is used to serve as a physical barrier to acetic acid in submerged fermentations
  • composition of lipid membrane is shifted to decrease the area available for passive transport of lipophilic molecule, like acetic acid.
51
Q

what are the 2 main steps in producing traditionally produced vinegars?

A
  1. production of ethanol from a CHO by a yeast (if starches are used, the starch is broken down by a fungi first)
  2. oxidation of ethanol to acetic acid by Acetobacter sp., Gluconobacter sp., or gluconacetobacter sp.
52
Q

what is the function of cellulose produced by AAB?

A

formation of biofilms that allow the retention of bacterial cells on the culture surface so they have access to O2 for oxidative fermentation

53
Q

what are examples of fermented foods involving AAB?

A

nata de coco: liquid coconut water surrounded by bacterial cellulose

kombucha

vit C (the Reichstein process was used to generate vitamin C, which includes one microbial step where Sorbitol is converted to sorbose by Komagataeibacter xylinus)

54
Q

in wine production, yeast is used as a ___ and sulfur dioxide is used as an _____

A

starter culture; antibacterial

55
Q

what does wine spoiled by AAB taste like?

A

sour, buttery, nutty or like bruised apples

5) Food Microbiology (21 decks)

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