Vegetable Fermentation

Traditional fermentations

Under appropriate conditions, most vegetables will undergo a spontaneous lactic acid fermentation

Example of natural microflora of plant: Anaerobes: 105-106; aerobes: 106-107

Coliforms: 104-105

LAB: 101-103

Yeasts: 101-103

Molds: 101-103

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

Making sauerkraut

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.

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

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

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

Sauerkraut Leuconostoc mesenteroides

Has relatively short lag phase and high growth rate at low temp (15-18C)

Heterofermentative pathway (lactic acid, acidic acid, CO2, 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)

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, CO2, 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

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.

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

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

Shift in microbial community Leuconostoc mesenteroides - dominant micro popln @ 21oC 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)

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

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.

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.

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.

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.

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.

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

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)

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