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Food Microbiology > Fermented Vegetable Products > Flashcards

Fermented Vegetable Products Flashcards

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1
Q

What are some common vegetable fermentation products?

A

sauerkraut, pickles, olives, kimchi, fermented radish, fermented mustard leaves

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2
Q

What are the microorganisms found naturally on fresh fruit/veg?

A

spoilage aerobic microbes, yeasts, molds, LAB

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3
Q

True/False: LAB are the dominant microbe on fresh produce

A

False; actually in lower numbers than other mesophiles

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4
Q

What allows LAB to outcompete other microbes?

A

Adapted for high sugar environment

creates organic acids, antimicrobial compounds, lowers pH

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5
Q

What causes mushy sauerkraut?

A

Spoilage organisms (break down plant material)

sterilization/heat treatment

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6
Q

What is the importance of brining? (3)

A

salt break down cabbage to release sugars (feed LAB)

released juices create anaerobic environment (prevent spoilage/oxidation)

salt inhibit spoilage microbes

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7
Q

What is the notable species in most veg ferments? What conditions can it withstand?

A 
Leuconostoc mesenteroides (LAB)
grows rapidly 
large range of conditions (5-35C, 0-5% brine, up to acidity 1.5-2%)
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8
Q

What is the metabolism of L. mesenteroides?

A 
heterolactic
convert sugars (suc, fruc, gluc) -> CO2, acetic and lactic acid
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9
Q

Vegetable fermentations should be done below ____. Why?

A

22C

L. mesenteroides does not grow well in higher temperatures -> less flavor molecules produced -> lower quality product

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10
Q

What makes L. mesenteroides important to the beginning of vegetable fermentation?

A 
create acidity (prevent spoilage)
produce flavor compounds
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11
Q

What happens once L mesenteroides has acidified the product to 2%? What microbe takes over?

A

L. mesenteroides is inhibited

Lb. plantarum takes over (LAB)

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12
Q

What microbe is dominant at the end of the veg ferment, and why? Why does the ferment stop?

A

Lb brevis
superior acid tolerance
sugars have been consumed

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13
Q

True/False: a veg ferment that has not reached absolute completion (sugars depleted) can be safely consumed and stored

A

True

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14
Q

When is a vegetable ferment usually halted and deemed ready?

A

After Lb. plantarum log phase ends (before Lb. brevis)

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15
Q

Two preparations of sauerkraut have a pH of 2.2% and 3%. What are the dominant species in each?

A

2.2%: Lb. plantarum

3%: Lb. brevis

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16
Q

List the dominant species in a veg ferment in order:

A

Beginning: L. mesenteroides
Middle: Lb. plantarum
End: Lb. brevis

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17
Q

True/False: phage infection is of big concern in vegetable fermentations

A

False; not a concern. If one species targeted, another will take over (not monoculture like dairy)

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18
Q

(higher/lower) temperatures will produce better quality sauerkraut, but (higher/lower) temperatures produce faster sauerkraut

What is the best range?

A

lower
higher

18-22C (20 days time)

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19
Q

What is the sugar content of cabbage?

What % salt should be added?

A

2.5% glucose, 2% fructose

2-3%

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20
Q

Why are the leaves and core of cabbage removed?

A

leaves may contain more non-LAB bacteria

core high in sucrose, L. mesenteroides convert to dextran -> slimy

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21
Q

Are the pathogens (enterobacter) on the raw vegetable of concern?

A

No. killed off (5 log decrease in first few days) by acid, salt

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22
Q

True/False: glucose and fructose continue decreasing through the veg ferment

A

False; glucose will actually increase in first few days (then decrease)

23
Q

Why does glucose levels increase in the first few days of sauerkraut fermentation?

A

slow release from cabbage

24
Q

What happens to acid content during cabbage fermentation? Is this reflected by pH?

A

increase, slows, keeps increasing at slower rate

yes, corresponds to pH

25
Q

The decrease in fructose corresponds to an increase in ____. Why?

A

mannitol

LAB use fructose as TEA -> converts to mannitol

26
Q

___ acid produced by ___ LAB during _____ of the cabbage ferment is important for final aroma

A

acetic
heterolactic
first 8 days

27
Q

True/False: lack of sugar is the limiting factor in the end of sauerkraut fermentation

A

False; limiting factor is acid

28
Q

What causes the diphasic growth curve in sauerkraut fermentation?

A

after 8 days, heterolactic LAB die

homolactic take over

29
Q

What are benefits of high vitamin C in sauerkraut, and how can this be maintained?

A

ascorbic acid protect against oxidation (keep color)

protect ascorbic acid by removing O2 in headspace

30
Q

True/False: the pickle industry commonly reuses brine.

A

True
Can use to store, prepare new batch, etc
(getting rid of brine is $$$)

31
Q

True/False: European sauerkraut is stronger than American sauerkraut

A

False. packed after 1 week (mildly acidic)

32
Q

What is the main difference between home sauerkraut and store bought?

A

commercial is pasteurized (no live LAB)

also causes mushiness

33
Q

Two samples of sauerkraut (white cabbage): 1 is tinged with pink, while one has grey-brown cabbage in the top layer. Are they safe to eat? What happened?

A

pink: yeast growth (discard)

grey-brown cabbage: oxidation (okay)

34
Q

How does kimchi differ from sauerkraut?

A 
different ingredients (napa cabbage, anchovy, radish, pepper paste)
more salt (5-10%) to wilt cabbage
heterolactic fermentation used to develop flavor, but no homolactic (put into fridge to halt)
less acidity (0.6%)
35
Q

How does white kimchi and traditional kimchi differ?

A

white: no red pepper
traditional: hetero and homolactic ferment

36
Q

How does fermentation affect vitamin content?

A

A: maintained
B: increased! (B12 notable)
C: maintained (if anaerobic)

37
Q

True/False: not all pickles are fermented products

A

true; can also just pasteurize and add acid

38
Q

commercial cucumber fermentation is done in _____ tanks. Why?

A

outdoor transparent fibreglass

allow UV to kill aerobic yeast

39
Q

What is contained in the solution added to the cucumbers for pickle production?

A

brine: 6% NaCl, 0.1-0.4% CaCl (for crispness)

40
Q

Is CO2 produced during cucumber fermentation? Why or why not?

A

No

HOMOLACTIC ferment only (due to high salt)

41
Q

What are “bloaters,” and what causes it? How can it be prevented?

A

hollow pickles, air pockets from CO2 made by bacteria

prevent by purging (removal of excess CO2 from tank)

42
Q

What causes CO2 production in pickle ferments?

A

cucumber respiration
decarboxylation of malate at beginning of ferment
LAB malolactic pathway

43
Q

What chemicals can be used to limit aerobic organisms in air purged ferments?

A

K sorbate, acetic acid

44
Q

Do cucumber fermentations require a starter culture? What is the microbe of choice?

A

No; but becoming common

Lb. plantarum (developed strain that does not decarboxylate malic acid)

45
Q

pickles can be stored in brine tanks for ___. Outdoor tanks require increased ____ to prevent _____.

A

1 year

salt; freezing damage

46
Q

What are the end concentrations in complete pickles?

A

1.5% lactic acid
pH 3.0
very little sugars

47
Q

what could cause a decrease in pH in a completed pickle?

A 
secondary fermentation (spoilage)
lactic acid decreases -> form propionic, butyric acid (STINK)
48
Q

C. botulinum is a concern in ______, _____ conditions.

A 
low acid (>4.6)
anaerobic
49
Q

What types of olives are fermented? What types are not?

A

fermented: Green, Natural black

not fermented: canned black

50
Q

how are green olives prepared?

A
  1. washed in lye (1-3% NaOH)
  2. washed, brined (10% NaCl)
  3. Fermented
51
Q

What purpose does alkali treatment have on olives?

A

reduce bitterness
decrease phenolic antimicrobial activity
make skin permeable, let sugars diffuse out

52
Q

What are the first species to colonize olive fermentations and why?

A 
Enterobacter, Bacillus, Citrobacter
alkali resistant (pH is still high from lye process)
53
Q

When does LAB colonize the green olive fermentation and what species?

A

after pH drop to 6

Lb. plantarum

54
Q

What is the difference between black and green olive fermentation?

A

Black is ripe, softer (green unripe)
no lye treatment for black
longer ferment (phenols still active, skin still intact)

Food Microbiology (21 decks)

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