fermentation

Examples of fermentation in the following topics:

• Fermentation Without Substrate-Level Phosphorylation

  • During fermentation, pyruvate is metabolised to various compounds.
  • Homolactic fermentation is the production of lactic acid from pyruvate; alcoholic fermentation is the conversion of pyruvate into ethanol and carbon dioxide; and heterolactic fermentation is the production of lactic acid as well as other acids and alcohols.
  • Fermentation does not necessarily have to be carried out in an anaerobic environment.
  • Sugars are the most common substrate of fermentation, and typical examples of fermentation products are ethanol, lactic acid, lactose, and hydrogen.
  • Give examples of various types of fermentation: homolactic, heterolactic and alcoholic

• Fermented Foods

  • Fermentation in simple terms is the chemical conversion of sugars into ethanol.
  • The science of fermentation is also known as zymology or zymurgy.
  • Historically, when studying the fermentation of sugar to alcohol by yeast, Louis Pasteur concluded that the fermentation was catalyzed by a vital force, called "ferments," within the yeast cells.
  • The "ferments" were thought to function only within living organisms.
  • Describe the process of fermentation and its use in the food industry

• Wine, Beer, and Alcohol

  • The production of alcohol in these drinks is based primarily on yeast fermentation.
  • There are hundreds of commercially available yeast strains for wine fermentation.
  • When making red wine, there is an additional fermentation step after alcoholic fermentation.
  • Two main species are used in the fermentation process: Saccharomyces cerevisiae (top-fermenting, since it forms foam on top of the wort) and Saccharomyces uvarum (bottom-fermenting).
  • Top-fermenting yeasts are used to produce ale, while bottom-fermenting produce lagers.

• Large-Scale Fermentations

  • There are various types of fermentation which occur at the industrial level such as ethanol fermentation and fermentation processes used to produce food and wine.
  • Fermentation can be carried out in aerobic conditions as well, as in the case of yeast cells which prefer fermentation to oxidative phosphorylation.
  • The process of ethanol fermentation occurs when sugars are converted into cellular energy.
  • In regards to alcohol production, yeast will induce fermentation and produce ethanol.
  • Fermentation is also utilized in the mass production of various recombinant products.

• Vinegar

  • Vinegar is a food product made by acetic acid bacteria that can ferment the alcohol in alcoholic liquids to acetic acid.
  • It is one of the foods together with beer, wine, bread and fermented dairy products, that is the result of fermentation by microorganisms and has been around for thousands of years.
  • The fermentation is performed usually by acetic acid bacteria, from the genus Acetobacter, from the alcohol in variety of sources (e.g., apple cider, wine, potatoes, fermented grain).
  • This acetic acid fermentation needs oxygenation.
  • There are bacteria that can convert sugars straight to acetic acid in anaerobic fermentation.

• Microbes and Dairy Products

  • Fermented milk or dairy products have been part of human diet since ancient times.
  • Various fermented products are made by different strains.
  • Lactic acid fermentation is performed most often by lactic acid bacteria.
  • Other fermented and widely consumed cultured dairy products include kefir (lactic acid bacteria and yeasts are used for the fermentation), sour cream (fermented cream), cultured buttermilk (fermented cow's milk with Streptococcus lactis or Lactobacillus bulgaricus only).
  • Most of the researched species were isolated from different fermented dairy products.

• Syntrophy and Methanogenesis

  • Bacteria that perform anaerobic fermentation often partner with methanogenic archea bacteria to provide necessary products such as hydrogen.
  • A frequently cited example of syntrophy are methanogenic archaea bacteria and their partner bacteria that perform anaerobic fermentation.
  • Only methanogenesis and fermentation can occur in the absence of electron acceptors other than carbon.
  • Fermentation only allows the breakdown of larger organic compounds, and produces small organic compounds that can be used in methanogenesis.
  • Without methanogenesis, a great deal of carbon (in the form of fermentation products) would accumulate in anaerobic environments.

• Clostridial and Propionic Acid Fermentation

  • Acetic acid is equally a co-metabolite of the organic substrates' fermentation (sugars, glycerol, lactic acid, etc.) by diverse groups of microorganisms which produce different acids: Propionic bacteria (propionate + acetate), Clostridium (butyrate + acetate), Enterobacteria (acetate + lactate), Hetero-fermentative bacteria (acetate, propionate, butyrate, valerate, etc.)
  • Hydrolytic bacteria form a variety of reduced end-products from the fermentation of a given substrate.
  • Thermoanaerobium brockii is a representative thermophilic, hydrolytic bacterium, which ferments glucose, via the Embden–Meyerhof Parnas Pathway.
  • The hydrolyzed compounds are fermented into volatile fatty acids (acetate, propionate, butyrate, and lactate), neutral compounds (ethanol, methanol), ammonia, hydrogen and carbon dioxide.
  • Acetic acid is equally a co-metabolite of the organic substrates' fermentation (sugars, glycerol, lactic acid, etc.) by diverse groups of microorganisms, which produce different acids:

• Detecting Acid and Gas Production

  • Gut bacteria, such as Escherichia coli, can typically ferment lactose; important gut pathogens including Salmonella enterica and most shigellas are unable to ferment lactose.
  • Shigella sonnei can ferment lactose, but only after prolonged incubation; it is referred to as a late-lactose fermenter.
  • Those bacteria unable to ferment lactose, often referred to as nonlactose fermenters (NLFs) metabolize the peptone in the medium.
  • E. coli O157:H7 differs from most other strains of E. coli in being unable to ferment sorbitol.
  • Most strains of E. coli ferment sorbitol to produce acid: E. coli O157:H7 can not ferment sorbitol, so this strain uses peptone to grow.

• Syntrophy

  • The fermentative bacteria gain maximum energy yield when protons are used as electron acceptor with concurrent H2 production.
  • As oxygen is not required, fermentative organisms are anaerobic.
  • Many organisms can use fermentation under anaerobic conditions and aerobic respiration when oxygen is present.
  • To avoid the overproduction of NADH, obligately fermentative organisms usually do not have a complete citric acid cycle.
  • Fermentative organisms are very important industrially and are used to make many different types of food products.