fermented vegetable products

Question 1

what are the primary commercial fermented vegetable products in canada?

Answer 1

• cucumber pickles
• olives
• sauerkraut => probiotic

Question 2

benefits of fermentation process for vegetables

Answer 2

results in nutritious foods (MO make vitamins) that mat be stored for 1 year or more at room temperature

Question 3

sauerkraut major ingredients, microorganisms

Answer 3

cabbage and salt

Leuconostoc mesenteroides, Lactobacillus brevis, Lactobacillus plantarum

Question 4

prior to fermentation, fresh fruit and vegetables harbor a variety of microorganisms which include …
what is the cell population range?

Answer 4

aerobic spoilage microflora, as well as yeasts and molds

10^4 to 10^6 CFU/g

Question 5

what method consists in adding salt to a vegetable?

Answer 5

brining

Question 6

what does brining produce?

Answer 6

the production of organic acids, and a variety of antimicrobial compounds by LAB

Question 7

fermentation process of vegetables

Answer 7

organic acids diffuse into the brine, and the low pH that results, influences microbial growth in the vegetable material

Question 8

what happens when the vegetable cells die?

Answer 8

sugars diffuse into the brine resulting in the rapid growth of LAB

Question 9

what causes destructive enzyme production in veg. fermentation?

Answer 9

spoilage bacteria => deterioration of the veg. material

proteases, lipases, amylases, nucleases, etc.

Question 10

about Leuconostoc mesenteroides

Answer 10

• important in the initiation of the fermentation of several vegetables (important for flavour development)
• grows more rapidly than other LAB over a range of temperatures (5-35C, cold sauerkraut) and brine concentrations (0-5%)
• grows until an acidity level of 1.5-2.0% is achieved

Question 11

what type of fermentation does Leuconostoc mesenteroides carry out?

Answer 11

hetereolactic fermentation of vegetable sugars (sucrose, fructose, glucose) and produces carbon dioxide and acids (lactic and acetic)
Carbon dioxide replaces air and provides the anaerobic conditions favorable for the stabilization of ascorbic acid and the natural color of the vegetables

Question 12

the acidity produced by …. eventually inhibits the growth of these … microbes in favor of more acid-tolerant … LAB

Answer 12

Leuconostoc mesenteroides and other LAB
heterofermentative
homofermentative

Question 13

which LAB survives the elevating lactic acid levels (above 2%)?

Answer 13

Lactobacillus plantarum

=> produces exclusively lactic acid from the remaining sugars

Question 14

….. will continue fermenting after L. plantarum until an acidity level of 2.5-3% is obtained, and there is no sugar left in the vegetables
=> can survive most harsh conditions (very low pH [acid], no food [no sugars])

Answer 14

Lactobacillus brevis

Question 15

unlike dairy fermentations, …. are NOT a problem for vegetable fermentation

Answer 15

bacteriophages

Question 16

Sauerkraut fermentation process

Answer 16

If given anaerobic conditions, at approximately 18-22C, and 2-3% salt concentration, LAB dominate the microbial community and are able to grow on the sugars from the cabbage (glucose and fructose)
=> no need for starter culture
- During the first 24-48 hours of the fermentation, Enterobacteriacea (enteric pathogens) drop 5-log, aerobes and LAB increase, carbon dioxide gas, lactic acid, and to a lesser extent acetic acid will be produced from the salted cabbage
- sucrose remains low, fructose is rapidly used, glucose increases for the first few days (slow release of the glucose from the cabbage leaves)
- total titratable acidity increases rapidly. slows. then increases again => decrease in pH

Question 17

The best quality sauerkraut is produced between 18-22C, why?

Answer 17

favours growth of Leuconostoc mesenteroides

Question 18

what happens at higher temperatures during sauerkraut fermentation?

Answer 18

• faster but of lesser quality: LAB don’t grow as well producing a much less complex flavour

Question 19

summary of temperatures during sauerkraut fermentation (3)

Answer 19

• Below 7.5C fermentation time can be up to 6 month, flavor good
• 18-22C fermentation time is ~20 days, optimal flavor
• 32-36C fermentation time is 10 days, flavor is poor

Question 20

why are the outer leaves removed when making sauerkraut?

Answer 20

to lower the non-LAB bacterial load

Question 21

why do we remove the core to the cabbage when making sauerkraut?

Answer 21

The core contains high levels of sucrose, which can lead to dextran formation by L. mesenteroides resulting in a slimy texture

Question 22

why is salt added during cabbage fermentation? (2)

Answer 22

1. To extract cabbage juice from the leaves to make the sugars and nutrients from the plant material readily available to the LAB
2. To keep non-LAB from spoiling the cabbage. LAB are resistant to moderate amounts of salts, non-LAB are less resistant

Question 23

why do we remove oxygen when making sauerkraut?

Answer 23

Removing the oxygen favors the growth of LAB, over the growth of molds

Question 24

what does the increase in mannitol correspond to in sauerkraut fermentation?

Answer 24

decrease in fructose
-> Heterofermentative lactic acid bacteria use fructose as an electron acceptor converting it to mannitol
Mannitol remains constant during extended fermentation

Question 25

initial heterolactic stage of sauerkraut fermentation results in the production of … and …

Answer 25

lactic acids and acetic acids (flavour)

Question 26

why is there a “shoulder” at day 8 of sauerkraut fermentation?

Answer 26

when the heterofermentative LAB die, and the second growth curve (diphasic growth) is created when the homofermentative bacteria become dominant

Question 27

what is the sauerkraut fermentation end point ?

Answer 27

21 days - includes mannitol and acetic acid at ~1% each and lactic acid at ~2%.
-> acid accumulation is the limiting factor

Question 28

ascorbic acid in sauerkraut fermentation

Answer 28

Ascorbic acid concentration decreases a little during the first days of the fermentation if the oxygen in the head space is not pumped out => oxidized by dissolved oxygen from the headspace
- If ascorbic acid remains high the sauerkraut retains a light straw colour, if the ascorbic acid decreases the kraut has a grey/brown colour.

Question 29

how are most commercial sauerkraut made?

Answer 29

pasteurized and then canned, killing all of the LAB (any heating above 41C will kill most LAB)

Question 30

kimchi fermentation is microbiologically similar to …. but uses Chinese cabbage/asian radishes instead

Answer 30

sauerkraut fermentation

Question 31

how is cabbage kimchi prepared?

Answer 31

• the fresh cabbage is cut in half and soaked in 5-10% brine to wilt the cabbage, the cabbage is drained, and a paste of red pepper is added
• The ingredients are packed into jars and held in “kimchi refrigerators” which provide a temperature of 18C for a few days followed by cold refrigeration (1-2C) – lower temp than traditional sauerkraut => HETEROLACTIC fermentation but halts the reaction before the homofermentative stage occurs (kimchi less sour than sauerkraut)

Question 32

which step occurs in sauerkraut fermentation but is halted in kimchi fermentation?

Answer 32

homofermentative stage

Question 33

what is then difference in acidity between kimchi and sauerkraut?

Answer 33

Kimchi has 0.6% acid vs. 2.5-3% in traditional sauerkraut

Question 34

how does traditional kimchi differ from cabbage kimchi?

Answer 34

has the diphasic heterofermentative and homofermentative pattern of LAB succession

Question 35

vitamin … content increases during sauerkraut and kimchi fermentation.
vitamins .. and .. are maintained (microbes don’t degrade them or make them)

Answer 35

B

A and C

Question 36

vitamin … could be found in fermented veg products

Answer 36

B12

Vitamin B12 found in animal products (can only be synthesized by bacteria found in animal guts)

Question 37

not all pickles are fermented pickles, what are the other types?

Answer 37

some can be pasteurized and canned in acid

Question 38

how is cucumber fermentation carried out in canada?

Answer 38

fermentations are done in 30,000 liter, open-top, fiberglass tanks located outside so the surface is exposed to sunlight

• Cucumbers are covered with salt brine and held below the surface with wooden headboards
• Fermentations generally have 6% NaCl and 0.1-0.4% calcium chloride to maintain the crisp texture of the fermented cucumber

Question 39

why do we expose the cucumbers to sunlight?

Answer 39

The UV radiation from the sunlight kills aerobic surface yeasts

Question 40

cucumber fermentations typically undergo … fermentation, which does not result in the production of CO2. Why?

Answer 40

homolactic fermentation

because the high salt concentrations favour homofermentative LAB

Question 41

how can CO2 be produced during cucumber fermentation?

Answer 41

• Carbon dioxide may be generated from the respiration of cucumbers and by the decarboxylation of malate (malolactic enzymes: convert malate to lactate and carbon dioxide) during the beginning of the fermentation reaction (bloater formation)

Question 42

what are “bloaters”? how do you avoid this?

Answer 42

happens when bacteria produce internal gas pockets in fermented cucumbers
=> cucumber fermentations are purged with air to remove excess CO2 from the tank which prevents bloater formation

Question 43

… or … can be used to limit the growth of aerobic organisms in air purged fermentations

Answer 43

potassium sorbate or acetic acid

Question 44

commercial cucumber fermentations

Answer 44

• rely on the growth of LAB naturally present on the cucumber, although the trend is now starting to be to use a Lactobacillus plantarum starter
• use recycled brine
• Some fermented cucumbers are pasteurized prior to sale, but further microbial growth is generally prevented by organic acids, low pH, and lack of fermentable sugars

Question 45

what is the environment at the end of cucumber fermentation? why is it good?

Answer 45

1.5% lactic acid, a pH of 3.0 (no Clostridium botulinum), and no residual sugar => Only a few types of microorganisms can grow in this environment

Question 46

fermented cucumber can undergo …. that spoils the product. what happens?

Answer 46

secondary fermentation - pH increases (above 4.6 Clostridium botulinum could be an issue), lactic acid decreases, propionic and butyric acids are formed -> stinky product

Question 47

what are the three principle types of commercial olives?

Answer 47

1. Green table olives (fermented)
2. Natural black olives (fermented)
3. Canned ripe black olives (not fermented)

Question 48

what treatment do green table olives undergo prior to fermentation?

Answer 48

• lye treatment (1-3% sodium hydroxide)

- Olives are washed and brined (10% NaCl) after alkali treatment

Question 49

why do we treat green table olives with a strong base (NaOH)? (3)

Answer 49

• It reduces the natural bitterness of olives
• It decreases the natural antimicrobial activities of the phenolic components of the olives
• It makes the skin of the olive more permeable allowing the sugar to diffuse out during fermentation (you want sugar to come out – fermentable substrate)

Question 50

due to the strong base treatment of the olives, what is the first microflora observed?

Answer 50

initial pH of fermentation above 7 -> resistance to alkali conditions: Bacillus sp. Enterobacter sp. Citrobacter sp.

Question 51

which LAB colonizes and dominated the green table olive fermentation once the pH drops below 6?

Answer 51

Lactobacillus plantarum

Question 52

what’s the difference between green table olives and natural black olives?

Answer 52

both are fermented but natural black olives DO NOT receive NaOH treatment prior to brining (much slower process)
=> they are picked in a ripened state and have a softer texture than green table olives

Question 53

why is the fermentation of natural black olives much slower than green table olives?

Answer 53

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