What are some common vegetable fermentation products?
sauerkraut, pickles, olives, kimchi, fermented radish, fermented mustard leaves
What are the microorganisms found naturally on fresh fruit/veg?
spoilage aerobic microbes, yeasts, molds, LAB
True/False: LAB are the dominant microbe on fresh produce
False; actually in lower numbers than other mesophiles
What allows LAB to outcompete other microbes?
Adapted for high sugar environment
creates organic acids, antimicrobial compounds, lowers pH
What causes mushy sauerkraut?
Spoilage organisms (break down plant material)
sterilization/heat treatment
What is the importance of brining? (3)
salt break down cabbage to release sugars (feed LAB)
released juices create anaerobic environment (prevent spoilage/oxidation)
salt inhibit spoilage microbes
What is the notable species in most veg ferments? What conditions can it withstand?
Leuconostoc mesenteroides (LAB) grows rapidly large range of conditions (5-35C, 0-5% brine, up to acidity 1.5-2%)
What is the metabolism of L. mesenteroides?
heterolactic convert sugars (suc, fruc, gluc) -> CO2, acetic and lactic acid
Vegetable fermentations should be done below ____. Why?
22C
L. mesenteroides does not grow well in higher temperatures -> less flavor molecules produced -> lower quality product
What makes L. mesenteroides important to the beginning of vegetable fermentation?
create acidity (prevent spoilage) produce flavor compounds
What happens once L mesenteroides has acidified the product to 2%? What microbe takes over?
L. mesenteroides is inhibited
Lb. plantarum takes over (LAB)
What microbe is dominant at the end of the veg ferment, and why? Why does the ferment stop?
Lb brevis
superior acid tolerance
sugars have been consumed
True/False: a veg ferment that has not reached absolute completion (sugars depleted) can be safely consumed and stored
True
When is a vegetable ferment usually halted and deemed ready?
After Lb. plantarum log phase ends (before Lb. brevis)
Two preparations of sauerkraut have a pH of 2.2% and 3%. What are the dominant species in each?
2.2%: Lb. plantarum
3%: Lb. brevis
List the dominant species in a veg ferment in order:
Beginning: L. mesenteroides
Middle: Lb. plantarum
End: Lb. brevis
True/False: phage infection is of big concern in vegetable fermentations
False; not a concern. If one species targeted, another will take over (not monoculture like dairy)
(higher/lower) temperatures will produce better quality sauerkraut, but (higher/lower) temperatures produce faster sauerkraut
What is the best range?
lower
higher
18-22C (20 days time)
What is the sugar content of cabbage?
What % salt should be added?
2.5% glucose, 2% fructose
2-3%
Why are the leaves and core of cabbage removed?
leaves may contain more non-LAB bacteria
core high in sucrose, L. mesenteroides convert to dextran -> slimy
Are the pathogens (enterobacter) on the raw vegetable of concern?
No. killed off (5 log decrease in first few days) by acid, salt
True/False: glucose and fructose continue decreasing through the veg ferment
False; glucose will actually increase in first few days (then decrease)
Why does glucose levels increase in the first few days of sauerkraut fermentation?
slow release from cabbage
What happens to acid content during cabbage fermentation? Is this reflected by pH?
increase, slows, keeps increasing at slower rate
yes, corresponds to pH
The decrease in fructose corresponds to an increase in ____. Why?
mannitol
LAB use fructose as TEA -> converts to mannitol
___ acid produced by ___ LAB during _____ of the cabbage ferment is important for final aroma
acetic
heterolactic
first 8 days
True/False: lack of sugar is the limiting factor in the end of sauerkraut fermentation
False; limiting factor is acid
What causes the diphasic growth curve in sauerkraut fermentation?
after 8 days, heterolactic LAB die
homolactic take over
What are benefits of high vitamin C in sauerkraut, and how can this be maintained?
ascorbic acid protect against oxidation (keep color)
protect ascorbic acid by removing O2 in headspace
True/False: the pickle industry commonly reuses brine.
True
Can use to store, prepare new batch, etc
(getting rid of brine is $$$)
True/False: European sauerkraut is stronger than American sauerkraut
False. packed after 1 week (mildly acidic)
What is the main difference between home sauerkraut and store bought?
commercial is pasteurized (no live LAB)
also causes mushiness
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?
pink: yeast growth (discard)
grey-brown cabbage: oxidation (okay)
How does kimchi differ from sauerkraut?
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%)
How does white kimchi and traditional kimchi differ?
white: no red pepper
traditional: hetero and homolactic ferment
How does fermentation affect vitamin content?
A: maintained
B: increased! (B12 notable)
C: maintained (if anaerobic)
True/False: not all pickles are fermented products
true; can also just pasteurize and add acid
commercial cucumber fermentation is done in _____ tanks. Why?
outdoor transparent fibreglass
allow UV to kill aerobic yeast
What is contained in the solution added to the cucumbers for pickle production?
brine: 6% NaCl, 0.1-0.4% CaCl (for crispness)
Is CO2 produced during cucumber fermentation? Why or why not?
No
HOMOLACTIC ferment only (due to high salt)
What are “bloaters,” and what causes it? How can it be prevented?
hollow pickles, air pockets from CO2 made by bacteria
prevent by purging (removal of excess CO2 from tank)
What causes CO2 production in pickle ferments?
cucumber respiration
decarboxylation of malate at beginning of ferment
LAB malolactic pathway
What chemicals can be used to limit aerobic organisms in air purged ferments?
K sorbate, acetic acid
Do cucumber fermentations require a starter culture? What is the microbe of choice?
No; but becoming common
Lb. plantarum (developed strain that does not decarboxylate malic acid)
pickles can be stored in brine tanks for ___. Outdoor tanks require increased ____ to prevent _____.
1 year
salt; freezing damage
What are the end concentrations in complete pickles?
1.5% lactic acid
pH 3.0
very little sugars
what could cause a decrease in pH in a completed pickle?
secondary fermentation (spoilage) lactic acid decreases -> form propionic, butyric acid (STINK)
C. botulinum is a concern in ______, _____ conditions.
low acid (>4.6) anaerobic
What types of olives are fermented? What types are not?
fermented: Green, Natural black
not fermented: canned black
how are green olives prepared?
- washed in lye (1-3% NaOH)
- washed, brined (10% NaCl)
- Fermented
What purpose does alkali treatment have on olives?
reduce bitterness
decrease phenolic antimicrobial activity
make skin permeable, let sugars diffuse out
What are the first species to colonize olive fermentations and why?
Enterobacter, Bacillus, Citrobacter alkali resistant (pH is still high from lye process)
When does LAB colonize the green olive fermentation and what species?
after pH drop to 6
Lb. plantarum
What is the difference between black and green olive fermentation?
Black is ripe, softer (green unripe)
no lye treatment for black
longer ferment (phenols still active, skin still intact)