Acetic Acid Bacteria Flashcards
What are some advantages of fermenting foods? (4)
- Improves organoleptic profile of food material
- Shelf life extended
- Availability of nutrients is improved
- Health-promoting properties may develop
What are the 3 ways of starting a fermentation reaction?
1) Spontaneous Fermentation
2) Inoculated Fermentation
3) Back slopping
Explain spontaneous fermentation
Which is based on the action of wild microorganisms that are already naturally on the food or in the area. You encourage the growth of certain microbes by creating optimal conditions for them (sauerkraut).
Explain inoculated fermentation
Which is based on introducing a single pure culture or several (mixed culture) into an environment that is favorable to their proliferation. The advantage is that it stabilizes fermentations which are sensitive to contamination (wine).
Explain back slopping
Which is based on adding the product of a previously successful fermentation reaction to start a new reaction (friendship bread in the 90’s)
Acetic fermentation produces _________
acetic acid
What are the2 things that must be present in acetic acid fermentation?
Alcohol and Oxygen (basically alcohol is being oxidized)
__________ is the most common name for acetic acid in the food industry
Vinegar
The hydrogen atom can separate from the rest of the molecule, by ____________, which gives acetic acid it’s acidic properties:
ionization
Can acetic acid be produced synthetically? (yes or no)
YES
Acetic Acid Bacteria (AAB) are a group of __________ bacteria that carry out oxidative fermentation to produce acetic acid from ethanol in a fermentation process.
Gram-negative, oxidative
Most vinegar is produced by which acetic acid bacteria?
Acetobacter sp
What are acetogenic bacteria?
bacteria that produce acetic acid anaerobically
Acetobacter sp is very tolerant to __________
acetic acid
Name the main 4 acetic acid bacteria:
Acetobacter, gluconobacter, gluconoacetobacter and Komagataeibacter
AAB live in __________, especially fruits and flowers, and can utilize either sugar or sugar alcohol for their energy sources and produce the corresponding sugar acids
sugar-rich niches
Why is the metabolism of acetic acid bacteria is somewhat unique?
because they oxidize substrates, and then use the accumulated products later
Gluconobacter can use several sugars or sugar alcohols such as (name 3) ______________________
D-glucose, D-sorbitol, and glycerol in addition to ethanol
Acetobacter and Komagataeibacter are only able to use ethanol? TRUE OR FALSE
TRUE
Name 4 common sugar alcohols:
Xylitol, Sorbitol, Mannitol & Glycerol
AAB are ________________ aerobes
obligate
Explain how you go from ethanol to acid acid?
- Alcohol dehydrogenase (ADH) takes electrons from the ethanol (or other sugar alcohol) and then transfers them to the terminal oxidase via ubiquinone.
- The oxidized alcohol become acetylaldehyde.
- Aldehyde dehydrogenase (ALDH) transfers electrons via ubiquinone (UQ) to oxygen as a final electron acceptor and the acetylaldehyde becomes acetic acid.
The complete oxidation of EtOH can occur in the _______________ (say where in the cell)
cytoplasm
Acetic acid produced in the cytoplasm can be utilized by ____________ (name the enzyme) and feed the tricarboxylic acid (TCA) cycle
acetyl CoA synthase
When strains oxidize acetic acid this is called _________________
overoxidation
Overoxidation results in what type of curve?
a biphasic growth curve
AAB can have a diauxic growth curve when the initial ethanol concentration is __________
below 1%
Name the 2 ways of carrying out acetic acid fermentations?
Surface static process and submerged process
Explain surface static process in acetic acid fermentation?
commonly use Acetobacter, and final concentrations can reach 8-9%. In this process AAB form a thin film on the surface of the growth media, which becomes thicker and more gelatinous with time. Bacteria (mother of vinegar) are embedded in this layer
Explain submerged process in acetic acid fermentation?
commonly use Komagataeibacter strains and may have acidities up to 15-20%. This involves rapid mixing with forced aeration in a bioreactor
Acetic acid is a ___________ acid that can readily diffuse though the cytoplasmic membrane of bacteria
weak lipophilic
How is acetic acid toxic ?
The toxic effect is caused by the dissociation of the proton when it encounters the higher pH of the cytoplasm
The release of the proton decreases the internal pH in the cytoplasm and causes the uncoupling of oxidative phosphorylation resulting in disruption of the proton gradient, resulting in poisoning of the cell
What are the 4 primary mechanism responsible for AAB resistance to acetic acid:
1) Prevention of acetic acid influx into the cell (CPS, EPS, LPS)
2) Acetic acid assimilation (overoxidation)
3) Acetic acid efflux (efflux pumps)
4) Protection of cytoplasmic proteins against denaturing (general stress proteins)
What are the 2 categories of molecular chaperones?
1) Those involved in the restoration of denatured/aggregated proteins.
2) Those involved in the degradation of denatured/aggregated proteins.
What are the 3 functions of molecular chaperones ?
1) Prevent denatured proteins from aggregating
2) Resolubilize aggregated proteins
3) Facilitating the degradation of seriously damaged proteins.
AAB produce large amounts of _________ that has a very unique, ultrafine structure
cellulose
What is the acetic bacteria involved in Nata de coco?
Komagataeibacter xylinum
What is the acetic acid bacteria involved in Kombucha?
Gluconacetobacter xylinus
Wine spoiled by AAB have what kind of taste ?
a vinegar like sourness, or can taste buttery, nutty or like bruised apples.
