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Food Microbiology > Yeast/Mold > Flashcards

Yeast/Mold Flashcards

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1
Q

The main species of yeast implicated in food science:

A

S. cerevisae

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2
Q

Where is S. cerevisiae normally found in nature?

A

surface of fruits (high sugar)

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3
Q

cell morphology of S. cerevisiae:

A

budding yeast
large size (5-10 microns)
round shape

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4
Q

What is the main metabolic process of yeast?

A

convert carbs into ethanol and byproducts

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5
Q

The metabolism of yeast is described by: ____ equation. Is it accurate?

A

Gay-Lussac equation: 180g sugar -> 92g ethanol, 82g CO2

real yield usually about 90-95%

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6
Q

What are the two types of proliferating yeast cells?

A

haploid or diploid

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7
Q

What happens to yeast when nutrients are depleted?

A

cells enter stationary phase; cease growing

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8
Q

How do stationary yeast cells differ from proliferating ones? (3)

A
  • appear round and bright
  • higher levels of storage carbs (trehalose and glycogen)
  • increased resistance to env. stresses
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9
Q

describe the sexual and asexual life cycles of yeast:

A

asexual: budding (haploid or diploid)
sexual: diploid produce ascus (4 haploid) -> haploids mate -> new diploid

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10
Q

The 2 types of haploid yeast cells:

How do they differ?

A 
alpha; a
produce pheromone (alpha or a type)
contain receptor for OPPOSITE type
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11
Q

What causes a haploid yeast to stop proliferating? (2)

A
  1. nutrient depletion (die or become stationary)

2. surface receptor stimulated -> mating process

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12
Q

What happens once a surface receptor on a haploid is stimulated?

A

stop proliferating in G1 phase -> start growing towards each other -> cell contact -> fusion -> forms diploid

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13
Q

The shape 2 haploids form during the mating process is known as a ____

A

schmoo

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14
Q

____ cells that are starved of ____ will begin the first step of sexual reproduction, ____.

A

diploid
NITROGEN
sporulation

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15
Q

True/False: stationary yeast are the most resistant form of yeast

A

false; ASCUS produced during sporulation is even more resistant to stresses

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16
Q

When does an ascus germinate?

A

When nutrients are present again

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17
Q

What is the “chitin ring” in yeast cell division?

A

form between mother and daughter cell at beginning of budding

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18
Q

How are cell materials transferred from mother to daughter cell? Why is this significant?

A

vesicles

limiting factor for rate of growth (growth of cell wall can only occur with necessary materials)

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19
Q

the 4 stages of yeast asexual proliferation:

A

G1, S, G2, M

20
Q

What is the resulting polarity of cells in haploid division? What about diploid division?

A

haploid: faces each other
diploid: faces away, or in same direction

21
Q

True/False: in the stationary phase of yeast cells, metabolic activity stops.

A

False: stationary cells use ethanol formed previously -> TCA cycle, glyoxalate cycle

22
Q

Growing yeast cells ferment sugar into ____ via ____.

A

ethanol; glycolysis

23
Q

Yeast is extremely notable for its ____ metabolism systems

A

carbohydrate

24
Q

___ and ___ can easily diffuse across the yeast cell membrane. Other substances require ______

A

ethanol, glycerol

special transport systems

25
Q

How are disaccharides processed by yeast?

A

secrete INVERTASE or GALACTOSIDASE -> monosaccharide -> taken up by specific transport system

26
Q

What disaccharide is taken up by yeast? What occurs?

A

actively transported across membrane
broken down by MALTASE
2 glucose -> glycolysis

27
Q

What disaccharide may be taken up by yeast or hydrolyzed first?

A

sucrose
broken down by periplasmic or cytoplasmic INVERTASE
fructose + glucose -> taken up by hexose transporter
-> glycolysis

28
Q

The yeast cell is surrounded by 3 outer layers:

A

plasma membrane
periplasmic space
cell wall

29
Q

The cell wall confers ___ to the yeast. What compound is responsible?

A

mechanical strength

chitin

30
Q

What is the composition of the yeast cell wall?

A

50% glucans
40% mannoproteins
10% chitin

31
Q

What microbes are necessary to degrade starch? How does it accomplish this?

A

Mold: Aspergillus oryzae

secrete various amylases

32
Q

What products utilize mold for fermentation?

A

soy sauce, meso (soybeans)

sake (rice)

33
Q

A oryzae is a ___ fungi.

A

filamentous

34
Q

Describe the process of reproduction in A oryzae:

A

produce CONIDIUM (spore) at tip of specialized hypha
conidium swells -> germ tube
forms HYPHAE, partitioned by septa

35
Q

What happens if one cell on the hyphae is damaged?

A

sensed by other hyphae through communication PORES

pores are “plugged” by WORONIN BODIES (cut off communication, nutrient exchange)

36
Q

what is the organelle in A oryzae involved in degrading starch? where is it located, and what is its role?

A

spitzenkorper
tip of hyphae
accumulate/secrete vesicles with secretory enzymes

37
Q

What makes A oryzae so efficient at degrading starch? (2)

A
  1. . large variety of amylases/debranching enzymes

2. re-uses enzymes (uptake into vesicles after release)

38
Q

What is the specialized hypha for sporulation?

A

Conidiophore

39
Q

What is the process of sporulation?

A

nutrients passed up from hyphae to forming conidia
germinate: conidia swell
vacuoles “push” cytoplasm into forming germ tube

40
Q

What are other molds used in food production?

A

Geotrichum candidum: moist cheese, prevent unwanted mold (diff flavors available)
Penicillium candidum (fuzzy white rind on cheese, diff flavors available)
Penicillium roqueforti: blue cheese (diff colors available)

41
Q

How might AAB, LAB, molds, and yeasts coexist symbiotically within an environment?

A

AAB and LAB poor at biosynthesis - feed off of substrates made by mold and yeast

42
Q

Why would AAB, LAB, mold, and yeast grow in different areas of a fermented product?

A

mold and AAB on surface - AEROBIC

yeast and LAB internal - ANAEROBIC

43
Q

what are some examples of symbiotic fermented products?

A

sake
kombucha
fukuyama pot vinegar
kefir

44
Q

How is sake produced and with what microbes?

A

Koji (mold) -> break down rice to sugars
LAB -> ferment sugar, kill wild yeast
brewing yeast -> second ferment -> produce sake

45
Q

Describe the process of fukuyama pot vinegar:

A

similar process to sake; pot left exposed to air
eventually levels of ethanol rise, mold taken over by AAB -> convert ethanol to acetic acid -> becomes vinegar, no longer alcoholic

46
Q

what microbes are found in kefir grains?

A

LAB, yeast, AAB, sometimes mold, possibly Bifidobacter
(L. kefiranofaciens, Lb spp, Lactococcus, Streptococcus, Leuconostoc
S. cerevisiae)

47
Q

What microbe is mainly responsible for forming the kefir grain? What microbe improves the quality of the kefir grain?

A

L. kefiranofaciens (forms EPS: KEFIRAN)

yeast will improve kefiran quality

Food Microbiology (21 decks)

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