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Page history last edited by Charles Forstbauer 10 years, 11 months ago

Closed 12/22 Mr F. 

Totaled 11/23 Mr F


     Fermentation is the process of deriving energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. This

process is the opposite of cellular respiration where electronsa are donated to an exogenous electron

acceptor, such as oxygen. Endogenous means from within and exogenous means from outside. Sugars

containing glucose are the most common substrate of fermentation.


  • Fermentation releases energy from food molecules in the absence of oxygen.
  • Because fermentation does not require oxyegen it is anaerobic  
  • Alcoholic Fermentation Equation:  C6H12O6 + ATP  ___________ Alcohol + CO2 + Pyruvate

                    - The purpose of Alcoholic Fermentation is to regenerate NAD+ to get more ATPs

  • Latic Acid Fermentation Equation: Pyruvic Acid + NADH ___________ Latic Acid + NAD
  • Latic Acid is produced in your muscles during rapid exercise when the body cannot supply enough oxygen to the tissues.
  • Without enough oxygen the body is not able to produce the required amount of ATP.


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     This video does a great job of showing on a diagram what Sabrina has just posted. It shows the paths for both alcoholic fermentation and lactic acid fermentation. It clearly points out how alcoholic fermentation occurs in yeast, and produces ethanol and carbon dioxide; also, how the lactic acid fermentation occurs in muscle and results in lactate.




Fermentation- process by which cells release energy in the absence of oxygen

Anaerobic- process that does not require oxygen

The two main types of fermentation are alcoholic fermentation and lactic acid fermentation.

Pyruvic acid + NADH ---> alcohol + CO2 + NAD+  

Pyruvic acid + NADH ---> lactic acid + NAD+

In the absence of oxygen, yeast and a few other microorganisms use alcoholic fermentation, forming ethyl alcohol and carbon dioxide as wastes.

Animals cannot perform alcoholic fermentation, but some cells, such as human muscle cells, can convert glucose into lactic acid. This is called lactic acid fermentation.

Yeast however, have more than one pathway for fermentation, and can be anaerobic, still able to function without oxygen. However, humans can not, for if we are deprived of oxygen, we will die. The only way we can ferment anything is lactic acid fermentation in muscles. But that will not help us live without oxygen.

There is also a third pathway, which will produce citric acid.


This is a diagram of anaerobic metabolism, which is also known as fermentation, showing possible products as a result, it shows how ATP and NADH energy and carriers come in and out of the process, as well as differences between yeast and muscles and what they can produce. As you can see, muscles are limited to two products, pyruvic and lactic acid.


There are two important ways a cell can harvest energy from food: fermentation and cellular respiration. Both start with the same first step: the process of glycolysis which is the breakdown or splitting of glucose (6 carbons) into two 3-carbon molecules called pyruvic acid. The energy from other sugars, such as fructose, is also harvested using this process. Glycolysis is probably the oldest known way of producing ATP. There is evidence that the process of glycolysis predates the existence of O2 in the Earth’s atmosphere and organelles in cells:


Lactic Acid Fermentation:



Lactic acid fermentation is a biological process by which sugars such as glucose, fructose, and sucrose, are converted into cellular energy and the metabolic product lactic acid. It is the anaerobic form of respiration that occurs in some bacteria and animal cells in the absence of oxygen. During homolactic acid fermentation, one molecule of glucose is ultimately converted to two molecules of lactic acid. In heterolactic acid fermentation, sometimes referred to as the phosphoketolase pathway, the products of fermentation are one molecule of carbon dioxide, one molecule of ethanol, and one molecule of lactic acid.


This video shows the process used during Fermentation.

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     Fermentation is what cells do when there is not enough oxygen.  When there is a lack of oxygen, cells need to do something with the Pyruvates, but they cannot perform the krebs cycle or the electron transport chain because those are both aerobic processes.  So cells perform fermentation, and different cells do it differently.


     Alcohol Fermentation.  This is the process which for example yeast use.  When there is a lack of oxygen, the cells start to produce CO2 and alcohol as waste.  This is the reason why yeast is used in baking.  Bread for example, wouldn'r rise without yeast, but it does rise because yeast creates CO2 which makes it rise.  The smell that you get from baking, is from the alcohol burning off.  The reason we do not get intoxicated when eating bread (because of the alcohol that is made from the fermentation) is because the alcohol is burned off during baking because of high temperatures.


     Lactic Acid Fermentation is done by animal cells.  In the abscence of oxygen, animal cells produce lactic acid to create more NAD+.  This is only temporary, and as it is aneorobic for longer, the cells will not be able to produce enough ATP.  WIth a lack of ATP, the cells will die.  That is why lactic acid fermentation is a last resort, and can only be done for so long. 


The point of fermentation is to regain NAD+ for glycolysis.



    Pyruvic Acid
Pyruvic Acid + 2 H+
arrow  or  arrow
Lactic Acid   Ethanol

Carbon Dioxide

Lactic Acid   Ethanol


Carbon Dioxide

  • Alcoholic Fermentation

The alcoholic beverages that can be produced by fermentation vary widely, depending primarily on two factors—the plant that is fermented and the enzymes used for fermentation. Human societies use, of course, the materials that are available to them. Thus, various peoples have used grapes, berries, corn, rice, wheat, honey, potatoes, barley hops, cactus juice, cassava roots, and other plant materials for fermentation. The products of such reactions are various forms of beer, wine or distilled liquors, which may be given specific names depending on the source from which they come. In Japan, for example, rice wine is known as sake. Wine prepared from honey is known as mead. Beer is the fermentation product of barley, hops, and/or malt sugar.

Early in human history, people used naturally occurring yeast for fermentation. The products of such reactions depended on whatever enzymes might occur in "wild" yeast. Today, wine-makers are able to select from a variety of specially cultured yeast that control the precise direction that fermentation will take.

Ethyl alcohol is not the only useful product of fermentation. The carbon dioxide generated during fermentation is also an important component of many baked goods. When the batter for bread is mixed, for example, a small amount of sugar and yeast is added. During the rising period, sugar is fermented by enzymes in the yeast, with the formation of carbon dioxide gas. The carbon dioxide gives the batter bulkiness and texture that would be lacking without the fermentation process.

  Fermentation has a number of commercial applications beyond those described thus far. Many occur in the food preparation and processing industry. A variety of bacteria are used in the production of olives, cucumber pickles, and sauerkraut from the raw olives, cucumbers, and cabbage, respectively. The selection of exactly the right bacteria and the right conditions (for example, acidity and salt concentration) is an art in producing food products with exactly the desired flavors. An interesting line of research in the food sciences is aimed at the production of edible food products by the fermentation of petroleum.

In some cases, antibiotics and other drugs and be prepared by fermentation if no other commercially efficient method is available. For example, the important drug cortisone can be prepared by the fermentation of a plant steroid known as diosgenin. The enzymes used in the reaction are provided by the mold Rhizopus nigricans.

One of the most successful commercial applications of fermentation has been the production of ethyl alcohol for use in gasohol. Gasohol is a mixture of about 90% gasoline and 10% alcohol. The alcohol needed for this product can be obtained from the fermentation of agricultural and municipal wastes. The use of gasohol provides a promising method for using renewable resources (plant material) to extend the availability of a nonrenewable resource (gasoline).

Another application of the fermentation process is in the treatment of wastewater. In the activated sludge process, aerobic bacteria are used to ferment organic material in wastewater. Solid wastes are converted to carbon dioxide, water and mineral salts.


  • Lactic Acid Fermentation

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 fermentation is used throughout the world to produce speciality foods:

  • Western world: yogurt, sourdough breads, sauerkraut, cucumber pickles and olives
  • 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: gari (fermented cassava)
  • South Africa : magou (fermented maize porridge)
  • Thailand : nham (fermented fresh pork)
  • Philippines : balao balao (fermented rice and shrimp mixture)

The presence of lactic acid, produced during the lactic acid fermentation is responsible for the sour taste and for the improved microbiological stability and safety of the food. This lactic acid fermentation is responsible for the sour taste of dairy products such as cheese, yoghurt and kefir. Lactic acid fermentation also gives the sour taste to fermented vegetables such as traditionally cultured sauerkraut and pickles. The sugars in the cabbage are converted into lactic acid and serve as a preservative.

Yogurt fermentation

Yogurt is made by fermenting milk with friendly bacteria, mainly Lactobacillus bulgaricus and Streptococcus thermophilus. Yogurt fermentation was invented probably by accident by Balkan tribes thousands of years ago. Yogurt remained mainly a food of eastern Europe until the 1900s, when the biologist Mechnikov created the theory that lactobacillus bacteria in yogurt are responsible for the unusually long lifespans of the Bulgar people.


The milk sugar or lactose is fermented by these bacteria to lactic acid which causes the characteristic curd to form. The acid also restricts the growth of food poisoning bacteria. During the yogurt fermentation some flavours are produced, which give yogurt its characteristic flavour.

Magou fermentation

Magou is very popular in South Africa, especially among the Bantu people. Magou is a lactic acid fermented porridge made from maize. To make magua a 10 percent maize meal slurry is cooked, cooled and inoculated with wheat flour, which contains the bacteria. Magou is also produced on industrial scale and is then packed in cartons. In the industrial process the magou is inoculated with

lactobacillus delbreuckii


Kefir fermentation

Kefir fermentation is similar to yogurt fermentation. Yogurt is only fermented by bacteria but kefir fermentation involves the help of bacteria as well as yeasts. These yeast produce some alcohol and carbon dioxide, which gives kefir its typical fizzy aspect. Kefir is inoculated with special kefir grains. These grains are mixtures of bacteria and yeasts in a matrix of proteins, lipids and carbohydrates. Kefir fermentation is done at room temperature, which makes the process easier. On the other hand, not everyone likes the taste of kefir.



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