1. Vegetable Fermentation

2. Traditional fermentations Under appropriate conditions, most vegetables will undergo a spontaneous lactic acid fermentation Example of natural microflora of plant:  Anaerobes: 10 5 -10 6 ; aerobes: 10 6 -10 7  Coliforms: 10 4 -10 5  LAB: 10 1 -10 3  Yeasts: 10 1 -10 3  Molds: 10 1 -10 3

3. Vegetable fermentation steps Harvest Wash Trim, and shred or size Brine ferment

4. Making sauerkraut

5. sauerkraut is "acidic cabbage." It is the result of a natural fermentation by bacteria indigenous to cabbage in the presence of 2 to 3% salt. The fermentation yields lactic acid as the major product. This lactic acid, along with other minor products of fermentation, gives sauerkraut its characteristic flavor and texture.

7. Vegetable fermentations Harvest  Special crop varieties for fermented vegetables  Growth conditions and harvest time affect sugar levels Wash  Minimal Trim  Remove damaged parts and core, shred, or sort by size

8. Key points for vegetable fermentation Natural fermentation  No heat process to inactive other flora  Natural lactic acid bacteria to carry out fermentation  LAB minor population, but dominant in successful product fermentation  Succession: the fermentation depends not on any single organism, but a consortium of bacteria representing several different genera and species. A given organism (or group of organisms) initiates growth and becomes established for a period of time. Due to accumulation of inhibitory compounds, growth slows down and gives way to other species that are less sensitive to those factors. (Fig. 7.3)  Bacteriophage may also have a role

9. Microbiology of sauerkraut fermentation A definite sequence of lactic acid bacterial species required Initiated by the heterofermentative Leuconostoc mesenteroides Followed by heterofermentative rods such as Lb. brevis, homofermentative Lb. plantarum and Pediococcus cerevisiae

11. Sauerkraut Leuconostoc mesenteroides  Has relatively short lag phase and high growth rate at low temp (15-18  C)  Heterofermentative pathway (lactic acid, acidic acid, CO 2, ethanol)  Acidic environment (0.6%-0.8%, as lactic acid) inhibit non- lactic competitor and favors other LAB  Acid approaches 1.0%, inhibit L. mensenteroides (4-6 days) Other homolactic bacteria Acidity 1.6%, pH below 4.0, only L. plantarum can grow Final acidity 1.7%, pH 3.4-3.6 (Fig 7-2)

13. Microbiology of sauerkraut fermentation Leuc. mesenteroides  Gas-forming  Rapid growth  Active over a wide range of temp and salt conc.  Produce lactic acid, acetic acid, CO 2, lower pH rapidly  Limit undesirable M/O and enzymes that might soften the cabbage shreds  Creates anaerobic atmosphere, prevent oxidation of ascorbic acid and darkening of natural color of the cut cabbage and stimulates growth of LAB Incidental M/O  G- coliform and pseudomonad types usually undetectable in a day or two

14. Microbiology of sauerkraut fermentation Lb. brevis, Lb. plantarum, Ped. cerevisiae increase rapidly Contribute to the major end products including lactic acid, acetic acid, carbon dioxide, ethanol Minor end products  Volatile compounds: diacetyl, acetyladehyde, sulphur compounds, ethyl butyrate, etc.

15. Microbiology of sauerkraut fermentation Control of salt of fermentation  Brine, flavor, control the growth of M/O Control of temp of fermentation  2.25% salt, 18°C (65°F) Temp increases, LAB sequence changes too  Lenc retarded, Lb dominant  At 32°C and above, homofermentation dominant, flavor and aroma deteriorated, reminiscent of acidified cabbage due to LA, darkened readily

16. Defects & spoilage of sauerkraut fermentation Discoloration (autochemical oxidation) Loss of acidity Off-flavor and odors (moldy, yeasty, rancid) Slimy Softened kraut and pink-colored kraut Due to aerobic growth of molds and/yeasts Control-create anaerobiosis

17.  Shift in microbial community Leuconostoc mesenteroides - dominant micro popln @ 21 o C grows well Produces mannitol Not inhibited by 2.5% salt  Up to 1% lactic acid accumulate  Yeast & various bacteria may grow as surface film  Continuing succession  Lactobacillus plantarum - produces acid (no gas) [Lactic acid] reaches 1.5-2% Growth removes mannitol (has bitter flavour)

18. Fermentation can be STOPPED  Canning or refrigeration Residual sugar & mannitol  after L. plantarum continues succession  L. brevis Increase [Lactic acid] to 2.4% Imparts bitter acid flavour High Quality Sauerkraut:  [Lactic acid] 1.7%  Low [diacetyl] contribute to flavour

19. To make sauerkraut the cabbage must be shredded to produce a large surface area for the growth of the microbes and to extract the plant juice nutrients which will be metabolized by the microbes. Sodium chloride (table salt) is added to a concentration of 3% to provide OPTIMUM CONDITIONS FOR GROWTH of the desired fermenting bacteria, to help EXTRACT the tissue juices, and to INHIBIT the growth of microbes (molds) that would ruin the cabbage.

20. The cabbage/salt mixture is weighted down to squeeze out the juices and incubated at room temperature in covered containers. The cover inhibits the entry of OXYGEN into the mixture and allows ANAEROBIC FERMENTATION occur. At the end of the fermentation period the pH should be ~ 2.0 and the sauerkraut should contain about 1% lactic acid.

21. The sauerkraut fermentation process utilizes the indigenous population of bacteria in the raw cabbage to produce lactic acid. This produces a low pH environment that allows few if any other bacteria to survive. The lactic acid is also what gives the kraut it's characteristic sour flavor. Salt is added to the raw cabbage to draw out much of the water (drier product keeps longer) and to inhibit salt-intolerant bacteria. This allows the acid producing bacteria to get a strong foot hold and dominate the population.

22. Throughout the fermentation, it is critical that oxygen be excluded. The presence of oxygen would permit the growth of some spoilage organisms, particularly the acid-loving molds and yeasts.

23. As no starter cultures are added to the system, this is referred to as a wild fermentation. The normal flora of the cabbage leaves is relied upon to include the organisms responsible for a desirable fermentation, one that will enhance preservation and organoleptic acceptability. The floral succession is governed mainly by the pH of the growth medium.

24. Pickle Production Any vegetable or fruit preserved by salt or acid Most important: cucumber 1 billion Kg in the US used for pickles (half of the crop) Now more than half of the pickles are not fermented (direct add acetic acid) Types  Fresh-packed (non-fermented)  Refrigerated (non-fermented)  Fermented (processed) Distinctive flavor and texture

26. Manufacture of fermented pickles Rely on salt, oxygen exclusion, anaerobiosis to select for growth of instead of dry salt Salt conc. higher than that for sauerkraut  Less diverse microflora  Brine at least 5% salt, some 7%-8%, up to 12%  Up to 2 months, end pH ~3.5, acidity 0.6%-1.2% (as lactic)  L. mensenteroides cannot grow  Initiated by L. plantarum and Pediococcus sp.  Brine condition inhibitory to coliforms and other non-LAB  De-salted after fermentation for further consumption Can use starters (controlled fermentation) (Fig 7-5)

27. Defects Pickles  Bloaters and floaters (Table 7-4) Excessive gas pressure, internal cavity formation LAB (heterolactic, malolactic fermentation), coliforms, yeasts Control: remove dissolved CO2 by flushing or purging with nitrogen gas Some can still be used  Destruction and softening Slippery, loses crispness and crunch Cannot be used Pectinolytic enzymes by microorganisms Fungi  Penicillium, fusarium, Alternaria, Aschyta, Cladosporium Control: acidity