9) Fermented Vegetables Flashcards
what is the function of brining vegetables? what process does this result in?
- production of organic acids and antimicrobial compounds by LAB
- organic acids diffuses into the brine, resulting in low pH which influences microbial growth
- as veg cells die, sugars diffuses into the brine, results in fast growth of LAB
- LAB holds up to the salt solution since they are resistant
differentiate a successful vs not successful sauerkraut fermentation
successful: sauerkraut will still by crunchy b/c bacteria has not broken CHOs yet
not successful: will be mushy due to breakdown of plant material by spoilage MOs
without brine, how does spoilage MOs grow? what does this result in?
without brine, spoilage MOs an grow which casues destructive enzyme production (proteases, lipases, etc…) which results in deterioration of veg material
what is an imp MO for initiation of veg fermentations?
characteristics?
Leuconostoc mesenteroides
- grows more rapidly than other LAB
- high resistance to salt conc (0-5%)
- will grow until acidity of 1.5-2%
- will not grow above 22C
describe the growth of Lactobacillus plantarum in veg fermentations
- able to survive elevating lactic acid levels (by L. mesenteroides and other LAB)
- produces lactic acid from remaining sugars (that were not fermented by L. mesenteroides)
- will grow above acidity of 2.0%
- will usually outcompete other LAB at the end of the rxn due to superior acid tolerance
- at end of log phase growth, there is little sugar left. The resulting veg ferment is acceptable to be served or canned
describe the growth of Lactobacillus brevis in veg fermentations
- will continue fermenting after L. plantarum
- until acidity of ~3% and when there is no sugar left to ferment
what are the 3 most imp MOs in veg fermentations?
rate them in order of growth in acid content
Leuconostoc mesenteroides (acid ~1.5%)
LAtobacillus plantarum (acid ~2%)
Lactobacillus brevis (acid ~3%)
are bacteriophages a problem for veg fermentations? why or why not
- not a problem b/c veg fermentations don’t use starter cultures. If phages are present and inhibit one strain of LAB, another resistant strain will grow instead
why are bacteriophages a problem for dairy fermentations?
they use starter cultures. If the starter culture is infected, the fermentation will fail
describe the production of sauerkraut. explain each step
- remove outer leaves: lowers non LAB bacterial load
- remove core: which has high sucrose levels and could lead to dextran formation by L. mesenteroid (slimy texture)
- add salt: so that
- cabbage juice will be extracted; makes sugars and nutrients available for LAB
- non-LAB will not spoil the cabbage (LAB are resistant to moderate salt levels, but non-LAB are not) - remove O2: by air lock or submerging in brine. This favours LAB growth over mold growth
describe the fermentation process of sauerkraut production.
–
compare commercial sauerkraut to homemade sauerkraut
commercial can be stored up to 1 year, but this may cause increasing sourness from lactic acid accumulation
generally pastuerized and canned. This kills all LAB (due to heat), which makes the cabbage less crispy
high levels of ascorbic acid is what color?
low levels is what color?
why is this?
does this effect taste?
high vit C levels: light straw color
low vit C levels: grey/brown color
due to oxidation of O2 during first few days if O2 is still present inside the jar
no effect to taste
descrbie the production of Kimchi
- cut and soak cabbage in brine
- drain cabbage
- add red pepper paste and other ingredients
- mixture is put into jars in “kimchi refrigerators” (18C), followed by col refrigeration (1-2C)
why does Kimchi need to be stored in cold refrigeration (1-2C) at end of production?
how does this compare to sauerkraut?
allows heterolactic fermentation to occur, but slows rxn before homofermentative stage occurs
this keeps kimchi from becoming as sour as sauerkraut
how do vit B, C and A levels change during fermentation?
B increases
C and A stay the same
what is the composition of cucumber salt brine?
6% NaCl
0.1-0.4 calcium chloride
what is the role of calcium chloride in cucumber salt brine?
to maintain crisp texture
what type of LAB fermentation does cucumber fermentation undergo?
homolactic fermentation
- favoured by high salt conc
- results in no CO2 production from fermentation
is CO2 produced in cucumber fermentation?
- not by the homolactic fermentation, but can be produced due to cucumber respiration and decarboxylation of malate at the start of rxn
what do malolactic enzymes do?
converts malate to lactate and CO2
malolactic enzymes can result in ____ during cucumber fermentations
describe this.
how can this be prevented?
bloaters
- when bacteria produces internal gas pockets
can prevent by:
- removing excess CO2 from tank
- adding potassium sorbate or acetic acid to limit growth of aerobic organisms
in commercial cucumber fermentations, what starter is used? why?
Lb. plantarum starter, with no de-carboxylate malic acid (thus, it won’t cause bloaters)
describe the conditions at the end of cucumber fermentation
describe growth of MOs. What is significant about this?
1.5% Lactic acid
pH 3
no residual sugar
not many MOs can grow here. Risk of spoilage is low
describe the second fermentation of cucumber
- occasionally occurs
- causes spoilage
- pH increases, lactic acid decreases
- propionic and butyric acids are formed (causes bad odor compounds)
- clostridium botulinum can be an issue
3 types of olives?
- green table: fermented
- natural black: fermented
- canned ripe black: not fermented
describe the treatment to green table olives before fermentation
why is this done?
treated with lye (1-3% NaOH) to:
- reduce natural bitterness of olives
- decrease natural antimicrobial activities of the phenolic compounds of olives
- make skin of olive more permeable to allow sugar to diffuse out during fermenting
describe the production of natural black olives
- no NaOH treatment before brining (thus, slower fermentation process). This is b/c antimicrobial phenolic compounds dissolves into the brine which slows fermentation_
- softer texture than green table olives
