Lactic Acid Bacteria

Question 1

Lactic acid can have 2 other names, what are they?

Answer 1

Milk acid or 2-Hydroxypropanoic acid

Question 2

In food fermentations, lactic acid is produced from the break-down of __________________

Answer 2

simple carbohydrates such as glucose, sucrose, or galactose by lactic acid bacteria (LAB).

Question 3

Homofermentative bacteria can produce _______________ from one mole of glucose:

Answer 3

two moles of lactate

Question 4

Heterofermentative species can produce ___________________ from one mole of glucose:

Answer 4

one mole of lactate from one mole of glucose, and produce carbon dioxide and acetic acid or ethanol as biproducts:

Question 5

What is the fermentable carbohydrate in the HHD agar ?

Answer 5

Fructose is the fermentable carbohydrate

Question 6

What is the pH indicator in HHD?

Answer 6

Bromo cresol green

Question 7

What is the color of the homofermentative colonies on HHD agar?

Answer 7

green

Question 8

What is the color of the heterofermentative colonies on HHD agar?

Answer 8

white

Question 9

Homofermentative lactic acid bacteria produce _____________ from fructose and is indicated by ________ colour formation.

Answer 9

lactic acid, yellow

Question 10

Heterofermentative lactic acid bacteria induce (more or less) ? acidification and thus vary in the colour formation by the indicator in the medium.

Answer 10

less

Question 11

Lactic Acid Bacteria (LAB) are a group of Gram _____________ bacteria that produce lactic acid during the fermentation of carbohydrates

Answer 11

positive

Question 12

are lactic acid bacteria spore-forming? YES OR NO

Answer 12

NO

Question 13

Tell me why lactic acid bacteria need nutrient-rich environements?

Answer 13

Because they have limited biosynthetic capability

Question 14

Name the main 5 LAB?

Answer 14

Lactococcus, Lactobacillus, Leuconostoc, Streptococcus and Enterococcus

Question 15

Only one Streptococcus species is associated with food, which one is it?

Answer 15

S.thermophilus (used in yogurt in co-culture with Lactobacillus delbruckii subsp. bulgaricus)

Question 16

What specie of lactococcus is used in dairy products?

Answer 16

Lactococcus lactis

Question 17

Name the 3 LAB that are trtrad-forming:

Answer 17

Aerococcus, Pediococcus and Tetragenococcus

Question 18

Leuconostoc, Oenococcus, and Weisella are each ________ LAB

Answer 18

coccoid

Question 19

Leuconostocs are important for what kind of fermentations?

Answer 19

spontaneous vegetable fermentations like sauerkraut

Question 20

Weissella species are associated with meat and can proliferate at (high or low) temperatures?

Answer 20

low

Question 21

___________ are the most acid-tolerant of the LAB, and will therefore be the final successors of many lactic acid fermentations.

Answer 21

Lactobacilli

Question 22

What are the 3 groups of lactobacillus?

Answer 22

Obligately homofermentative, obligately heterofermentative and facultatively heterofermentative

Question 23

What do LAB do avoid concentration gradients?

Answer 23

They phosphorylate all in-coming sugars

Question 24

Explain Obligately Homofermentative:

Answer 24

sugars are only fermented by glycolysis

Question 25

Explain Obligately Heterofermentative:

Answer 25

only the 6-PG/PK pathway is available for fermentation, key enzymes for glycolysis are missing

Question 26

Explain Facultatively Heterofermentative:

Answer 26

use glycolysis for hexose fermentation, but some sugars induce a heterolactic fermentation reaction to take place

Question 27

_________ can be cleaved into acetate and oxaloacetate, and oxaloacetate can be a terminal electron acceptor in several pathways

Answer 27

citrate

Question 28

__________ can be terminal electron acceptor in anaerobic glucose fermentation

Answer 28

glycerol

Question 29

___________ can be an electron acceptor for heterofermentative LAB

Answer 29

fructose

Question 30

___________ is a permanent threat in LAB fermentation commercial processes

Answer 30

Phage infection

Question 31

Name the 4 naturally occurring phage defense mechanisms (ABRA)?

Answer 31

- Absorption inhibition - Blocking DNA penetration - Restriction enzymes - Abortive infection mechanisms

Question 32

Name the 4 artificial occurring phage defense mechanisms (ACCP)?

Answer 32

- Antisense RNA strategies - Clone ORI - Clone in a phage repressor - Phage triggered death

Question 33

Which LAB has been shown to have the greatest ability to remove mycotoxins from foods&

Answer 33

Lactobacillus rhamnosus

Question 34

What are mesophilic starter cultures in cheese production?

Answer 34

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.

Question 35

What are thermophilic starter cultures in cheese production?

Answer 35

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).

Question 36

The lactic acid fermentation of sauerkraut is initiated by ________

Answer 36

Leuconostoc mesenteroides

Question 37

__________ is the final LAB in sauerkraut fermentation

Answer 37

Lactobacillus plantarum