Lactic Acid Fermentation

• Starting fermentable sugar (glucose, lactose). (Figure 1 and Figure 2).
• Microorganisms (lactic acid bacteria or fungi). (Figure 3).

Figure 1. Lactose

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Figure 1. Lactose

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Figure 2. Glucose

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Figure 2. Glucose

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Figure 3. Microorganisms

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Figure 3. Microorganisms

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See Figure 4.

Figure 4. Lactic Acid Fermentation

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Figure 4. Lactic Acid Fermentation

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• 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 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.

Homolactic fermentation

• The fermentation of 1 mole of glucose yields two moles of lactic acid

Heterolactic Fermentation

• 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.

Homofermenter

• Enterococcus faecium
• Enterococcus faecalis
• Lactobacillus acidophilus
• Lactobacillus lactis
• Lactobacillus delbrueckii
• Lactobacillusleichmannii
• Lactobacillus salivarius
• Streptococcus bovis
• Streptococcus thermophilus
• Pediococcus acidilactici
• Pedicoccus damnosus
• Pediococcus pentocacus

Facultative homofermenter

• Lactobacillus bavaricus
• Lactobacillus casei
• Lactobacillus coryniformis
• Lactobacillus curvatus
• Lactobacillus plantarum
• Lactobacillus sake

Obligate heterofermenter

• Lactobacillus brevis
• Lactobacillus buchneri
• Lactobacillus cellobiosus
• Lactobacillus confusus
• Lactobacillus coprophilus
• Lactobacillus fermentatum
• Lactobacillus sanfrancisco
• Leuconostoc dextranicum
• Leuconostoc mesenteroides
• Leuconostoc paramesenteroides

• 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

• 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)

• Sauerkraut
• Pickles

• Lactic acid fermentations are carried out under three basic types of conditions:
  • dry salted
  • brined
  • non-salted
• Salting provides a suitable environment for lactic acid bacteria to grow which imparts the acid flavor to the vegetable.

• 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.

Figure 5. Making Sauerkraut

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Figure 5. Making Sauerkraut

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Figure 6. Spoonful of Sauerkraut

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Figure 6. Spoonful of Sauerkraut

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• 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.

• 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

• 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.

Figure 7. Pickles

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Figure 7. Pickles

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