vegetable fermentation

Origin of vegetable fermentation

Began with the practice of salting vegetables for preservation; low salt is more economical and more palatable if fermentation occurs

Shelf life of fermented vegetables

Can be stored 1 year or more without refrigeration

Water content of cabbage

92-94% (carbohydrate 5-6%, protein 1%)

Composition of cucumbers

Water 95%, carbohydrate 2-3%, protein 1%

Composition of olives

Water 78-80%, carbohydrate 2-4%, protein 1-2%, fat 12-14%

Which vegetable substrate has notable fat content?

Olives (12-14% fat)

Dry salting

Salt added directly to the vegetable to draw fluid out of it (e.g., sauerkraut)

Brine salting

Vegetable submerged in salt solution; salt equilibrates with the vegetable (e.g., pickles)

Three preservation mechanisms in vegetable fermentation

1) Low pH (lactic acid) 2) Carbon dioxide 3) Anaerobic conditions (low oxidation-reduction potential)

Is an inoculum/starter needed for vegetable fermentation?

No; LAB are naturally present at very low levels on fresh vegetables

Which organism initiates vegetable fermentation?

Leuconostoc mesenteroides

Leuconostoc mesenteroides role

Initiates fermentation; grows rapidly, producing lots of CO2 and moderate lactic acid

What happens as pH drops during vegetable fermentation?

Other LAB take over: Pediococcus, Lactobacillus plantarum, Lactobacillus brevis

Pediococcus cerevisiae (acidilactici)

LAB found in most fermented vegetable products

Lactobacillus plantarum in vegetable fermentation

Essential in all products; major acid producer

Lactobacillus brevis

Heterofermentative LAB that ferments pentose sugars

LAB succession in vegetable fermentation

Leuconostoc mesenteroides -> Pediococcus -> L. brevis -> L. plantarum

Starter culture properties for fermented vegetables (growth)

Minimal nutritional requirements; grows at low temperatures; ferments diverse carbohydrates; rapid growth and acid production

Starter culture properties for fermented vegetables (tolerance)

Tolerant of acid/low pH, salt, and antimicrobial phenolics; resistant to bacteriophage; competes against many organisms

Starter culture properties for fermented vegetables (other)

Produces desirable flavor; minimal loss of viability during storage

Best salt concentration for most vegetable fermentations

2-2.5%

Best temperature for vegetable fermentation

Cool (basement or cave temperature)

Fermentation container requirements

Must allow gas to escape and prevent airborne contamination

Most defects in fermented vegetables are caused by

Microorganisms, when production conditions (temperature, salt) are not controlled, causing deviations in fermentation pattern

Rhodotorula sp. in sauerkraut

Yeast that causes pink pigment defect (associated with salt problems)

Sauerkraut salting method

Dry salt on shredded cabbage

Pickle

Vegetable (or fruit) preserved by salt or acid

Most popular pickled vegetable

Cucumber

Pickle origin path

India -> Middle East -> Europe

Most common acid in fermented pickles

Lactic acid

Non-fermented pickles

Use acetic acid (vinegar) as the pickling acid, omitting the fermentation step

Three pickle groups by manufacture

Fresh-packed, refrigerated, salt-stock (genuine)

Fresh-packed pickles

Cucumbers packed in jars with vinegar and flavorings, then heat pasteurized; long shelf life at room temp; crisp, mildly acidic; most popular

Refrigerated pickles

Not pasteurized, kept refrigerated; crisp, bright green; shorter shelf life; sodium benzoate usually added; slight fermentation may occur

Salt-stock (genuine) pickles

The only fully fermented pickles; distinct flavor and texture; take much longer to make; shelf life about 2 years

Which pickle type is fully fermented?

Salt-stock (genuine) pickles

Preservative usually added to refrigerated pickles

Sodium benzoate

Salt concentration in fermented pickles vs. sauerkraut

Higher than sauerkraut; brine (>5% salt) used instead of dry salt

Cucumbers used for fermented pickles

Only small, immature cucumbers

Cucumber to brine ratio

1:1

Salt-stock pickle salt level

7-8% salt

Dill-type pickle salt level

7.5-8.5% salt

Brine salt <5% in pickle fermentation

L. mesenteroides can grow; heterofermentation gives diverse flavor but causes bloater/floater defects; unwanted Bacillus, Pseudomonas, Flavobacterium grow

Brine salt 5-8% in pickle fermentation

Leuconostoc inhibited; fermentation initiated by Pediococcus and L. plantarum

Pickle brine pH

Below 4.5; inhibits coliforms, pseudomonads, bacilli, clostridia; LAB survive

Why can't salt-stock pickles be eaten as is?

Very sour and salty; must be rinsed and soaked in water to remove salt and acid, then processed

Bloaters and floaters

Defect from excessive gas pressure (CO2) in cucumbers

Preventing bloaters and floaters

Remove dissolved CO2 by flushing/purging the brine with nitrogen gas

Reversible softening of pickles

Calcium removed from pectin; reversed by adding calcium chloride during processing

Nonreversible softening of pickles

Pectinase enzyme action, caused by high pH and high fermentation temperature

Minimizing nonreversible softening

Exclude cucumber flowers; maintain salt, acidity, and anaerobiosis; partially acidify with acetic acid

Preventing mold and aerobic yeast growth in pickles

Cover the containers

Main use of raw olives

Olive oil (90%); table olives only 7-10%

Origin of olives

Middle East; hardy tree can live up to 1,000 years

Olive production in the US

Where are fermented olives most popular?

Europe

Share of US olives that are not fermented

70% (simply brined and canned)

Olive picking stage

Most picked while still green, straw-yellow, or cherry-red

Olive phenolic compounds

Contribute to color; antimicrobial against many organisms (including LAB); antioxidant dietary benefits

Most important and abundant olive phenol

Oleuropein

Oleuropein

Glucoside ester of 3,4-dihydroxytyrosol and elenolic acid; causes bitter flavor

Oleuropein content over ripening

3-6% early; 1-2 mg/g after maturing

Olive composition

12-30% oil; 2-5% fermentable carbohydrate (glucose)

Spanish-style (green) olives

Treated with lye (NaOH) and fermented

Greek-style (naturally black) olives

Not lye-treated, but fermented

Ripe-black / California-style olives

Lye-treated but NOT fermented; aeration oxidizes pigments from green to black

Which olive styles are lye-treated?

Spanish-style (then fermented) and California ripe-style (not fermented)

Which olive style is not lye-treated?

Greek-style (naturally black)

Spanish-style lye treatment

0.5-3.5% lye for 4-12 hours at 15-20 C to de-bitterize by hydrolyzing oleuropein; followed by 1-3 rinse cycles

Spanish-style fermentation conditions

Brine 10-15% salt, 22-26 C, pH < 8.0; glucose may be added to restore sugar loss

Spanish-style stage 1

First 2-4 days: coliforms, Pseudomonas, Bacillus, Clostridium and other Gram-negative and Gram-positive bacteria grow

Spanish-style stage 2

Growth of L. mesenteroides and Pediococcus

Spanish-style stage 3

pH < 5: L. plantarum, L. brevis, L. fermentum grow

Spanish-style stage 4

pH 3.5-4.2: facultative yeasts grow; avoid Propionibacterium acnes (ferments lactic acid)

Greek-style olive fermentation

Bitter (no lye); fermented by LAB plus yeast, non-LAB bacteria, even fungi; produces lactic, acetic, citric, malic acids, CO2, ethanol; pH > 4.5

Ripe/California-style darkening reaction

Oxygen drives oxidation; phenolics polymerize into brown then black pigments

Olive spoilage susceptibility

More susceptible to microbial spoilage than other fermented vegetables

Fish eyes (olives)

Defect from excessive gas production

Olive tissue softening

Caused by pectin hydrolysis

Zapatera spoilage

Olive spoilage with foul, fecal, cheesy odors; caused by Clostridium species producing formic, propionic, butyric, valeric, caproic, caprylic acids

Preventing olive spoilage

Salt > 7.5% and pH < 4.0