See Figure 4.
- Lactic acid fermentation is caused by some fungi and bacteria.
- The most important lactic acid producing bacteria is Lactobacillus.
- Other bacteria which produce lactic acid include:
- leuconostoc mesenteroides
- pediococcus cerevisiae
- streptococcus lactis
- Bifidobacterium bifidus
Lactic Acid Bacteria
- Lactic acid bacteria refers to a large group of beneficial bacteria that have similar properties and all produce lactic acid as an end product of the fermentation process.
- They are widespread in nature and are also found in our digestive systems.
- The fermentation of 1 mole of glucose yields two moles of lactic acid
- The fermentation of 1 mole of glucose yields 1 mole each of lactic acid, ethanol, and carbon dioxide
- Nisin was the first bacteriocin derived from fermentation of a lactic-acid bacterium
- Approved by the FDA in April 1989 to prevent the growth of botulism spores in pasteurized process-cheese spreads.
- Does not inhibit Gram0negative organisms, yeasts, or fungi, but does inhibit most Gram-positive organisms including spore-formers such as Clostridia botulinum and heat-resistant spoilage organisms.
- Enterococcus faecium
- Enterococcus faecalis
- Lactobacillus acidophilus
- Lactobacillus lactis
- Lactobacillus delbrueckii
- Lactobacillus salivarius
- Streptococcus bovis
- Streptococcus thermophilus
- Pediococcus acidilactici
- Pedicoccus damnosus
- Pediococcus pentocacus
- Lactobacillus bavaricus
- Lactobacillus casei
- Lactobacillus coryniformis
- Lactobacillus curvatus
- Lactobacillus plantarum
- Lactobacillus sake
- Lactobacillus brevis
- Lactobacillus buchneri
- Lactobacillus cellobiosus
- Lactobacillus confusus
- Lactobacillus coprophilus
- Lactobacillus fermentatum
- Lactobacillus sanfrancisco
- Leuconostoc dextranicum
- Leuconostoc mesenteroides
- Leuconostoc paramesenteroides
Conditions for Lactic Acid Fermentation
- Addition of a sufficient amount of fermentable carbohydrates
- Reduced O2 during the fermentation process and storage of the fermented product.
- Rapid multiplication of the starter culture and sufficient production of lactic acid
Lactic Fermentation Products
- Western world: yogurt, sourdough breads, Western world: yogurt, sourdough breads, sauerkraut, cucumber pickles and olives
- Fermented meats
- Middle East: pickled vegetables
- Korea: kimchi (fermented mixture of Chinese cabbage, radishes, red pepper, garlic, and ginger)
- Russia: kefir
- Egypt: laban rayab and laban zeer (fermented milks), kishk (fermented cereal and milk mixture)
- Nigeria: Nigeria: gari (fermented cassava)
- South Africa: magou (fermented maize porridge)
- Thailand: nham (fermented fresh pork)
- Philippines: balao balao (fermented rice and shrimp mixture)
- Lactic acid fermentations are carried out under three basic types of conditions:
- dry salted
- Salting provides a suitable environment for lactic acid bacteria to grow which imparts the acid flavor to the vegetable.
How does salt preserve food?
- The chloride ion is a bacterial poison.
- Limits moisture availability.
- Oxygen solubility is reduced.
- Dehydrates protoplasm causing plasmolysis.
- Interfere with enzyme action.
- Generally, yeast, bacteria, and molds do not grow in saturated salt solution at 26.5% sodium chloride at room temperature.
- Vegetable is treated with dry salt.
- The salt extracts the juice from the vegetable and creates the brine.
- As soon as the brine is formed, fermentation starts and bubbles of carbon dioxide begin to appear.
- Fermentation takes between one and four weeks, depending on the ambient temperature.
- Sauerkraut literally translates as acid cabbage. (Figure 5 and Figure 6).
- Leuconostoc mesenteroides.
- Lactobacillus plantarum.
- Shredded cabbage is placed in a jar and salt is added.
- Mechanical pressure is applied to the cabbage to expel the juice, which contains fermentable sugars, and other nutrients suitable for microbial activity.
- The first micro-organisms to start acting are the gas-producing cocci (L. Mesenteroides). These microbes produce acids.
- When the acidity reaches 0.25 to 0.3% (calculated as lactic acid), these bacteria slow down and begin to die off, although their enzymes continue to function.
- The activity initiated by the L. mesenteroidesis is continued by the lactobacilli (L. plantarum and L. Cucumeris) until an acidity level of 1.5 to 2% is attained.
- The high salt concentration and low temperature inhibit these bacteria to some extent.
- Finally, L. pentoaceticus continues the fermentation, bringing the acidity to 2 to 2.5% thus completing the fermentation.
- The optimum temperature for sauerkraut fermentation is around 21º C.
- A variation of just a few degrees from this temperature alters the activity of the microbial process and affects the quality of the final product.
- Therefore, temperature control is one of the most important factors in the sauerkraut process.
- A temperature of 18º to 22º C is most desirable for initiating fermentation since this is the optimum temperature range for the growth and metabolism of L. mesenteroides.
Effects of Salt
- Imparts firmness
- Inhibits putrefactive bacteria formation
- Withdraws water from the cabbage
- Added to a final concentration of 2.0 to 2.5%
- Aerobic soil micro-organisms break down the protein and produce undesirable flavor and texture changes
- Dark colored sauerkraut (caused by spoilage organisms)
- Pink kraut is a spoilage problem. It is caused by a group of yeasts which produce an intense red pigment in the juice and on the surface of the cabbage
Brine Salted Fermented Vegetables
- For vegetables which inherently contain less moisture.
- A brine solution is prepared by dissolving salt in water (a 15 to 20% salt solution).
- Fermentation takes place well in a brine of about 20 salometer.
- The vegetable is immersed in the brine and allowed to ferment.
- The strong brine solution draws sugar and water out of the vegetable, which decreases the salt concentration.
- It is crucial that the salt concentration does not fall below 12%, otherwise conditions do not allow for fermetnation. To achieve this, extra salt is added periodically to the brine mixture.
- The washed cucumbers are placed in large tanks and salt brine (15 to 20%) is added.
- The cucumbers are submerged in the brine, ensuring that none float on the surface - this is essential to prevent spoilage.
- The strong brine draws the sugar and water out of the cucumbers, which simultaneously reduces the salinity of the solution.
- In order to maintain a salt solution so that fermentation can take place, more salt has to be added to the brine solution.
- If the concentration of salt falls below 12%, it will result in spoilage of the pickles through putrefaction and softening
- The color of the cucumber surface changes from bright green to a dark olive green as acids interact with the chlorophyll (Figure 7).
- The interior of the cucumber changes from white to a waxy translucent shade as air is forced out of the cells.
- The specific gravity of the cucumbers also increases as a result of the gradual absorption of salt and they begin to sin in the brine rather than floating on the surface.
Publication date: Aug. 8, 2005
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