Lecture 6 (Fermentation)

Question 1

Fermentation is an _________ process.

Answer 1

Anaerobic

Question 2

Where does fermentation occur in both eukaryotes and prokaryotes?

Answer 2

Cytoplasm for both

Question 3

What types of microbes use fermentation?

Answer 3

Some anaerobes and facultative anaerobes (yeast and bacteria)

Question 4

T/F: Fermentation uses oxygen as the final electron acceptor

Answer 4

F (uses an organic molecule, lie pyruvate or aldehyde)

Question 5

What is the goal of fermentation for the microbe?

Answer 5

To regenerate NAD+ that will be used in the next round of glycolysis

Question 6

What are the 3 byproducts of fermentation?

Answer 6

1) Acids
2) Alcohol
3) CO2

Question 7

T/F: Fermentation is useful for both us and the microbe

Answer 7

T (food, alcohol, indirect benefits for microbe)

Question 8

What are some examples of acidic fermentation?

Answer 8

1) Homolactic fermentation
2) Heterolactic fermentation
3) Mixed acid fermentation
4) Butanediol pathway

Question 9

What is an example of alcoholic fermentation?

Answer 9

Ethanol fermentation

Question 10

Microbes that use alcoholic fermentation can tolerate relatively high ________ concentrations.

Answer 10

alcohol

Question 11

What microbes use alcoholic fermentation?

Answer 11

Some yeast and bacteria

Question 12

What is the process of alcoholic fermentation?

Answer 12

Pyruvate –> Acetaldehyde –> Ethanol (Pyruvate is oxidized to produce ethanol, and produces NAD along the way which will be used for future glycolysis)

Question 13

What microbe naturally ferments simple sugars (starch, glucose, fructose) to ethanol?

Answer 13

S. cerevisiae (also most commonly used for beer, wine, fuel)

Question 14

________ is a major carbohydrate source for fuel ethanol

Answer 14

Corn (S.cerevisiae is added to corn for the ethanol fermentation process)

Question 15

What is the common vintner’s yeast?

Answer 15

S. cerevisiae

Question 16

What is the process of alcoholic fermentation for wine production (6 steps)?

Answer 16

1) Grape are pressed, forming must
2) Pasteurization (sometimes)
3) Fermentation (added yeast = induced fermentation)
4) Storage/aging for flavor development
5) Filtration
6) Bottling

Question 17

What are the 2 lactic acid pathways?

Answer 17

1) Homolactic fermentation
2) Heterolactic fermentation

Question 18

What is the process of homolactic fermentation?

Answer 18

Pyruvate -> Lactic acid (NAD is also produced to be re-used for glycolysis)

Question 19

For what reasons do we exploit homolactic fermentation?

Answer 19

Dairy, meat, and vegetable fermentation (yogurt, sour cream, some cheeses, sausage, pickled veggies)

Question 20

What are some examples of lactic acid bacteria that homolactic fermentation?

Answer 20

1) Lactobacillus sp.
2) Lactococcus sp.

Question 21

What is the process of heterolactic fermentation?

Answer 21

Pyruvate –> Lactic acid + CO2 + ethanol (NAD also produced)

Question 22

What are some examples of lactic acid bacteria and microbes that heterolactic fermentation?

Answer 22

1) Leuconostoc sp
2) Lactobacillus sp
3) some yeast

Question 23

What are some examples of products that are formed via heterolactic fermentation?

Answer 23

Veggies, dairy products, bread (Sauerkraut, pickled veggies, kefir, yogurt, sourdough, kombucha)

Question 24

What is the process for producing yogurt via either homolactic or heterolactic fermentation (7 steps)?

Answer 24

1) Raw milk
2) Homogenization, pasteurize (kill pathogens)
3) Cooling (to ~40 degrees)
4) Mixing (Milk w/LAB starter)
5) LAB Fermentation
6) Cooling (stops fermentation, bacteria still alive)
7) Yogurt!

Question 25

T/F: The finished yogurt product from homolactic/heterolactic fermentation can be used as a starter culture for the next batch

Answer 25

T

Question 26

Lactic acid bacteria use __________ and __________ fermentation.

Answer 26

homolactic and heterolactic

Question 27

T/F: Some LABs are naturally found in the human intestinal tract

Answer 27

T (the more fermented foods you eat, the more LAB you will have in your gut)

Question 28

LAB are often used as _________ for their potential health-promoting benefits

Answer 28

probiotics

Question 29

What microbes use mixed acid fermentation?

Answer 29

members of the Enterobacteriaceae family

Question 30

What is added to the process during induced fermentation?

Answer 30

Yeast

Question 31

Why is yeast added during induced fermentation?

Answer 31

1) Acts as a catalyst
2) Contains enzymes that can convert sugars into alcohol and CO2
3) Metabolizes the carb. molecules without oxygen

Question 32

What does mixed acid fermentation produce?

Answer 32

Lactic acid, formic acid, acetic acid, ethanol, and gases

Question 33

What are 2 key aspects of members of the Enterobacteriaceae family, which partake in mixed acid fermentation?

Answer 33

1) Can lower the pH of a medium to 4.0
2) Many members inhabit gut of humans and animals (“enterics”)W

Question 34

Why aren’t the intestines acidic?

Answer 34

Bicarbonate in mucus balances the acidity

Question 35

T/F: the butanediol pathway is an acidic pathway although acid is not a final product

Answer 35

T

Question 36

What occurs during the butanediol pathway that is used by some bacteria?

Answer 36

It diverts metabolism away from acid production and toward the formation of more neutral compounds like butanediol
(Pyruvate -> LA -> Acetoin -> Butanediol)

Question 37

What pH is required for enzymes that use the butanediol pathway?

Answer 37

6.0

Question 38

What are the products of fermentation?

Answer 38

1) Alcohol
2) Acids
3) Gases
4) NAD+
5) a little ATP (Glycolysis yields 2 ATP)

Question 39

Do fermentative microbes grow slower than non-fermenters?

Answer 39

Not really, many fermenters may have a faster rate of glycolysis