Lactic Acid Bacteria Flashcards
Lactic acid can have 2 other names, what are they?
Milk acid or 2-Hydroxypropanoic acid
In food fermentations, lactic acid is produced from the break-down of __________________
simple carbohydrates such as glucose, sucrose, or galactose by lactic acid bacteria (LAB).
Homofermentative bacteria can produce _______________ from one mole of glucose:
two moles of lactate
Heterofermentative species can produce ___________________ from one mole of glucose:
one mole of lactate from one mole of glucose, and produce carbon dioxide and acetic acid or ethanol as biproducts:
What is the fermentable carbohydrate in the HHD agar ?
Fructose is the fermentable carbohydrate
What is the pH indicator in HHD?
Bromo cresol green
What is the color of the homofermentative colonies on HHD agar?
green
What is the color of the heterofermentative colonies on HHD agar?
white
Homofermentative lactic acid bacteria produce _____________ from fructose and is indicated by ________ colour formation.
lactic acid, yellow
Heterofermentative lactic acid bacteria induce (more or less) ? acidification and thus vary in the colour formation by the indicator in the medium.
less
Lactic Acid Bacteria (LAB) are a group of Gram _____________ bacteria that produce lactic acid during the fermentation of carbohydrates
positive
are lactic acid bacteria spore-forming? YES OR NO
NO
Tell me why lactic acid bacteria need nutrient-rich environements?
Because they have limited biosynthetic capability
Name the main 5 LAB?
Lactococcus, Lactobacillus, Leuconostoc, Streptococcus and Enterococcus
Only one Streptococcus species is associated with food, which one is it?
S.thermophilus (used in yogurt in co-culture with Lactobacillus delbruckii subsp. bulgaricus)
What specie of lactococcus is used in dairy products?
Lactococcus lactis
Name the 3 LAB that are trtrad-forming:
Aerococcus, Pediococcus and Tetragenococcus
Leuconostoc, Oenococcus, and Weisella are each ________ LAB
coccoid
Leuconostocs are important for what kind of fermentations?
spontaneous vegetable fermentations like sauerkraut
Weissella species are associated with meat and can proliferate at (high or low) temperatures?
low
___________ are the most acid-tolerant of the LAB, and will therefore be the final successors of many lactic acid fermentations.
Lactobacilli
What are the 3 groups of lactobacillus?
Obligately homofermentative, obligately heterofermentative and facultatively heterofermentative
What do LAB do avoid concentration gradients?
They phosphorylate all in-coming sugars
Explain Obligately Homofermentative:
sugars are only fermented by glycolysis
Explain Obligately Heterofermentative:
only the 6-PG/PK pathway is available for fermentation, key enzymes for glycolysis are missing
Explain Facultatively Heterofermentative:
use glycolysis for hexose fermentation, but some sugars induce a heterolactic fermentation reaction to take place
_________ can be cleaved into acetate and oxaloacetate, and oxaloacetate can be a terminal electron acceptor in several pathways
citrate
__________ can be terminal electron acceptor in anaerobic glucose fermentation
glycerol
___________ can be an electron acceptor for heterofermentative LAB
fructose
___________ is a permanent threat in LAB fermentation commercial processes
Phage infection
Name the 4 naturally occurring phage defense mechanisms (ABRA)?
- Absorption inhibition
- Blocking DNA penetration
- Restriction enzymes
- Abortive infection mechanisms
Name the 4 artificial occurring phage defense mechanisms (ACCP)?
- Antisense RNA strategies
- Clone ORI
- Clone in a phage repressor
- Phage triggered death
Which LAB has been shown to have the greatest ability to remove mycotoxins from foods&
Lactobacillus rhamnosus
What are mesophilic starter cultures in cheese production?
Mesophilic cultures grow in temperatures of 10–48C, with the optimum around 38 C. Mesophilic starter cultures, composed of acid-forming lactococci, are often flavor producers, and are used in the production of many cheese varieties, fermented milk products, and ripened cream butter.
What are thermophilic starter cultures in cheese production?
starter cultures have their optimum growth temperature between 48C and 58C. Thermophilic starters are used for yogurt and for cheese varieties with high cooking temperatures (e.g. Emmental or Gruyere).
The lactic acid fermentation of sauerkraut is initiated by ________
Leuconostoc mesenteroides
__________ is the final LAB in sauerkraut fermentation
Lactobacillus plantarum
