Fermented vegetable products Flashcards
The primary commercial fermented vegetable products in Canada include:
- cucumber pickle (can be acidified, pasteurized and refrigerated)
- Olives
- Sauerkraut
Prior to fermentation, fresh fruit and vegetables harbor a variety of microorganisms including (3):
aerobic spoilage microflora, as well as yeasts and molds
Brining the vegetables (adding salt) results in the production of __________________by LAB
organic acids, and a variety of antimicrobial compounds by LAB
LAB are initially present on fresh vegetables in (higher or lower) numbers compared to other mesophilic organisms
lower
Explain what happens during vegetable fermentations (organic acids…..)
- During the fermentation, organic acids diffuse into the brine, and the low pH that results, influences microbial growth in the vegetable material
- As the vegetable cells die, sugars diffuse into the brine resulting in the rapid growth of LAB
- In the absence of brine, spoilage microbiota are able to grow
- Spoilage bacteria result in the deterioration of the vegetable material due to the elaborate destructive enzymes produced (proteases, lipases, amylases, nucleases, etc.)
_____________ are important in the initiation of the fermentation of several vegetables
Leuconostoc mesenteroides
Name a few characteristics of L.mesenteroides
1) grows more rapidly than other LAB over a range of temperatures (5-35) and brine concentrations (0-5%)
2) carries out heterolactic fermentation of vegetable sugars typically glucose sucrose and fructose and produces CO2 and acid (lactic and acetic)
3) The carbon dioxide that it produces replaces air and provides anaerobic conditions favorable for the stabilization of vit c and the natural color of vegetables
L. mesenteroides will grow until an acidity level of ______ is achieved
1.5-2.0%
If the temperature is above ______ L. mesenteroides will not grow, and this will be detrimental to the development of the fermentation
22C
___________ are able to survive the elevating lactic acid levels and produce exclusively lactic acid from the remaining sugars
Lb. plantarum
Lb.plantarum will grow above an acidity of ____
2%
Why will Lb.plantarum outcompete other LAB at the end of the fermentation reaction?
due to its higher acid tolerance
__________ will continue fermenting after Lb.plantarum until an acidity level of 2.5-3% is obtained and there’s no sugar left in the vegetables
Lactobacillus brevis
TRUE OR FALSE: Bacteriophages are a problem for vegetable fermentation
FALSE
Explain the relationship between vegetables fermentations, starter cultures and phages
Vegetable fermentations do not typically use starter cultures, but if phages are present and inhibit one strain of LAB, another resistant indigenous strain will grow instead.
If given _________ conditions, at approximately ___C, and ____% salt concentration, LAB dominate the microbial community able to grow on the sugars from the cabbage
anaerobic
22
2-3%
TRUE OR FALSE: High-quality sauerkraut can be produced without a starter culture if the conditions are correct
TRUE
During the first 24-48 hours what will be produced from the salted cabbage (sauerkraut fermentation)? (3)
- CO2
- lactic acid
- acetic acid
Explain the relationship between sauerkraut quality and temperature
- Temperature is important, the best quality sauerkraut is produced between 18-22C, since this temperature favors the growth of L. mesenteroides
- Generally, lower temperatures produce higher quality sauerkraut
- Higher temperature can produce sauerkraut in 7-10 days but it will be of lesser quality, LAB don’t grow as well during fast fermentation producing a much less complex flavor
Why are the outer leaves removed in sauerkraut fermentation?
To lower the non-LAB bacterial load
Why do we remove the core of the cabbage in sauerkraut fermentation
Because the core contains high levels of sucrose which can lead to dextran formation by L.mesenteroides resulting in a slimy texture
Give me the 2 reasons why we add salt in sauerkraut fermentation:
1) To extract the cabbage juice from the leaves to make the sugars ans nutrients from the plant material readily available to the LAB
2) To prevent non-LAB from spoiling the cabbage, non-LAB are less resistant to high amounts of salt
Why removing the oxygen is important in sauerkraut fermentation?
Because it favors the growth of LAB over the growth of mold
What happens to sucrose, fructose and glucose during sauerkraut fermentation?
- sucrose remains at low levels
- fructose is rapidly used
- glucose increases for the first few days
What happens to titratable acidity during sauerkraut fermentation?
- it increases rapidly
- slows
- then increases again but at a slower rate
What causes the increase in mannitol at the beginning of the fermentation reaction of sauerkraut?
the decrease in fructose
-Heterofermentative lactic acid bacteria use fructose as an electron acceptor converting it to mannitol
The fermentation end point of sauerkraut (21 days) includes mannitol and acetic acid at ~% each and lactic acid at ~%.
1
2
There is still sugar in the final sauerkraut, ___________ is the limiting factor
acid accumulation
What happens to the concentration of ascorbic acid during the first days of fermentation if the oxygen in the head space is not pumped out?
the ascorbic acid concentration decreases because it is oxidized by dissolved oxygen from the head space
What is the relationship between sauerkraut color and ascorbic acid concentration?
If ascorbic acid remains high the sauerkraut retains a light straw colour, if the ascorbic acid decreases the kraut has a grey/brown colour.
Most commercial sauerkraut products are pasteurized and then canned, killing all of the __________________
LAB (any heating above 41C will kill most LAB)
What are the 2 primary ingredients in Kimchi?
- Chinese cabbage
- Asian radishes
Is kimchi more or less acidic than sauerkraut ?
less
Explain the main steps in kimchi fermentation: (6)
1) Cabbage is cut in half
2) Cabbage is soaked in 5-10% brine to wilt the cabbage
3) Cabbage is drained
4) Paste of red pepper is added
5) The ingredients are packed into jars and held in kimchi refrigerators at temp 18C for a few days
6) Cold refrigeration (1-2C)
Why is kimchi less acidic?
Because the fermentation allows the heterolactic fermentation to take place, but halts the reaction before the homofermentative stage occurs
White kimchi contains no _______
red pepper
what is special about Traditional kimchi?
it has the diphasic heterofermentative and homofermentative pattern of LAB succession
____________ content increases during sauerkraut and kimchi fermentation
vitamin B
___________ and ________ are maintained during sauerkraut and kimchi fermentation
vit c and vit a
Are all pickles fermented pickles?
no some can be pasteurized and canned in acid
In cucumber fermentation, the UV radiation from the sunlight kills what :
aerobic surface yeasts
Cucumber fermentations typically undergo ___________ fermentation, which does not result in the production of carbon dioxide
homolactic
In cucumber fermentation: the high salt concentrations favor _______________ LAB
homofermentative
Some LAB have inducible malolactic enzymes that converts _____ to ________
malate
lactate and CO2
CO2 can cause _______ in cucumber fermentation
bloaters (this happens when bacteria produce internal gas pockets in fermented cucumbers)
What is done to prevent bloater formation in cucumber?
cucumber fermentations are purged with air to remove excess CO2 from the tank
__________ or ________ can be used to limit the growth of aerobic organisms in air purged fermentations
potassium sorbate or acetic acid
What is the new trend in cucumber fermentation?
the use of Lb.plantarum starter culture that does not decarboxylate malic acid (no bloaters)
What happens if a secondary fermentation occurs in fermented cucumbers? (pH, lactic acid,etc)
pH increases
lactic acid decreases
propionic and butyric acids are formed (stink)
What are the 3 principle types of commercial olives:
1) green table olives (fermented)
2) natural black olives (fermented)
3) canned ripe black olives (not fermented)
Explain the treatment of green table olives:
1) strong base treatment 1-3 % NaOH
2) the strong base reduces bitterness, decreases natural antimicrobial activities of the phenolic compounds
3) makes skin of the olive more permeable to allow sugars to diffuse out during fermentation
4) olives are washed with 10% NaCl
In what way the fermentation of natural black olives is different from the fermentation of green table olives ?
they do not receive NaOH treatment prior to brining
Explain the steps in natural black olives fermentation:
1) They are picked in a ripened state and have a softer texture than green table olives
2) Fermentation is a much slower process with black olives because of the lack of NaOH treatment:
- Antimicrobial phenolic compounds dissolve into the brine, slowing fermentation
- Diffusion of sugars out of the olives is slower in black olives
3) As a result this fermentation can take months to complete
