Lena Savoie
Fermentation is a process that occurs in the absence of oxygen, and there are two types: alcoholic and lactic acid fermentation. Both processes are used by cells to extract energy from glucose when oxygen is unavailable, but they differ in their products and the organisms that carry them out. Lactic acid fermentation produces lactic acid and occurs in some bacteria and animal cells, such as muscle cells, whereas alcoholic fermentation produces ethanol and carbon dioxide and is carried out by yeasts and some bacteria.
| Characteristics | Values |
|---|---|
| Types | Alcoholic fermentation, Lactic acid fermentation |
| Process | Alcoholic fermentation produces ethanol, carbon dioxide, and NAD+. Lactic acid fermentation produces lactic acid (lactate) and NAD+ |
| Occurrence | Alcoholic fermentation is carried out by yeasts and some types of bacteria. Lactic acid fermentation occurs in some bacteria and muscle cells |
| Use | Alcoholic fermentation is used in the production of alcoholic beverages and bread. Lactic acid fermentation provides energy when oxygen is low |
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What You'll Learn
The products of alcoholic fermentation
Alcoholic fermentation is a biochemical process that converts sugars and other carbohydrates into alcohol and carbon dioxide through the action of microorganisms, primarily yeast or bacteria. The process broadly consists of two parts: glycolysis and fermentation.
During glycolysis, glucose is broken down into two pyruvate molecules. The pyruvate molecules are then converted into two molecules of carbon dioxide and two ethanol molecules during the fermentation stage. The ethanol and carbon dioxide are transported to the exterior of the cell by simple diffusion.
The redox balance of alcoholic fermentation is achieved by regenerating NAD+ during the reduction of acetaldehyde to ethanol, which is catalysed by alcohol dehydrogenase. This process also results in the generation of NADH. The regeneration of NAD+ allows glycolysis to continue so that more ATP can be made.
In addition to ethanol and carbon dioxide, other compounds are generated during alcoholic fermentation, such as esters, higher alcohols, succinic acid, glycerol, 2,3-butanediol, and diacetyl. The production of these compounds can vary depending on the yeast strain and fermentation conditions.
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The products of lactic acid fermentation
Alcoholic and lactic acid fermentation are two types of fermentation processes. Fermentation occurs in the absence of oxygen, following glycolysis, and preceding the Krebs cycle and oxidative phosphorylation.
Lactic acid fermentation produces lactic acid (lactate) and NAD+. The NAD+ cycles back to allow glycolysis to continue, producing more ATP.
Lactic acid fermentation is the anaerobic conversion of a sugar source to lactic acid. This process is carried out by lactic acid bacteria (LAB) species, as well as yeast and even humans.
Lactic acid fermentation has been used in food production for thousands of years, particularly in the production of dairy products. Milk naturally contains lactic acid bacteria, and the fermentation process occurs spontaneously at an adequate temperature. This process was discovered by early farmers as a way to digest fresh milk, which is nearly indigestible by adults in its fresh form. The fermentation process introduces the enzymes needed to digest lactose, allowing adults to consume milk. Longer fermentation times were used in cheesemaking, with recipes for cheese production appearing in the earliest written documents, such as Cuneiform scripts and Babylonian and Egyptian texts.
In modern times, lactic acid fermentation is still used in food production, particularly in the production of yogurt and cheese. The most commercially important genus of lactic acid-fermenting bacteria is Lactobacillus, although other bacteria and yeast are also used.
The French chemist Louis Pasteur first described lactic acid as the product of microbial fermentation in 1857. Pasteur's work contradicted the purely chemical understanding of fermentation held by Liebig and his followers. Pasteur discovered the main mechanism of microbial lactic acid fermentation, describing fermentation as a "form of life without air".
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The process of alcoholic fermentation
Alcoholic fermentation, also known as ethanol fermentation, is a biological process that converts sugars and other carbohydrates into alcohol and carbon dioxide. This process is facilitated by microorganisms, primarily yeast or bacteria, and does not require oxygen, making it anaerobic. The yeast Saccharomyces cerevisiae is the most important agent of alcoholic fermentation, widely used in various fermentation industries, including wine, beer, cider, and bread.
The pyruvate molecules then undergo further breakdown to produce acetaldehyde and carbon dioxide, eventually yielding ethanol. This step requires electrons from NADH, resulting in the generation of NAD+. The NAD+ is recycled to enable the continuation of glycolysis and the production of more ATP.
Alcoholic fermentation is commonly employed in the production of alcoholic beverages. It is the basis for wine, beer, cider, and spirits, as well as bread-making. Yeasts consume sugars in the dough, generating ethanol and carbon dioxide as waste products. The carbon dioxide forms bubbles, causing the dough to rise. Additionally, alcoholic fermentation finds applications in the treatment of agro-industrial effluents, reducing the toxicity of organic compounds by transforming them into ethanol.
Furthermore, alcoholic fermentation occurs naturally in some species of fish, such as goldfish and carp, providing them with energy when oxygen levels are low. It is also observed in certain yeasts that can produce ethanol even in the presence of oxygen if they have the right nutritional conditions.
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The process of lactic acid fermentation
Lactic acid fermentation is a metabolic process that occurs in some bacteria and animal cells, such as muscle cells. It is an anaerobic process, meaning it takes place in the absence of oxygen. During lactic acid fermentation, glucose or other six-carbon sugars are converted into cellular energy and the metabolite lactate, which is lactic acid in solution. This process can be summarized in the following equation:
\< co: 11> \[ \ce{C_3H_3O_3} \: \text{(pyruvate)} \: + \ce{NADH} \rightarrow \ce{C_3H_6O_3} \: \text{(lactic acid)} \: + \ce{NAD^+}\]
In this equation, pyruvate, a 3-carbon molecule, is converted to lactic acid, also a 3-carbon molecule, through the reduction of pyruvate. This reaction also regenerates NAD+, which is essential for the continued production of ATP through glycolysis.
Lactic acid fermentation is particularly important in muscle cells during periods of strenuous exercise or when the oxygen supply is insufficient. This process allows for the production of ATP, providing energy for short bursts of increased activity. For example, ruffed grouse use lactic acid fermentation in their wing and breast muscles to achieve quick bursts of speed and escape from predators. Similarly, humans may experience muscle fatigue and pain associated with lactic acid accumulation during strenuous exercise when their respiratory and cardiovascular systems cannot deliver oxygen to the muscles fast enough.
Lactic acid fermentation also has important applications in food production and preservation. For instance, milk fermentation has been used since prehistoric times, possibly beginning with the Neolithic Revolution. Milk naturally contains lactic acid bacteria, which multiply during fermentation and produce enzymes that aid in digesting lactose. Traditional dishes from various Asian cuisines, such as burong isda from the Philippines, narezushi from Japan, and pla ra from Thailand, involve fermenting fish with rice to produce lactic acid, which preserves the fish. Additionally, lactic acid fermentation is the primary method for producing yogurt by fermenting milk with bacteria like Lactobacillus bulgaricus and Streptococcus thermophilus. These bacteria produce lactic acid, causing the milk to thicken and develop a tangy flavour.
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The uses of alcoholic fermentation
Alcoholic fermentation, also known as ethanol fermentation, is a biological process that converts sugars such as glucose, fructose, and sucrose into cellular energy, producing ethanol and carbon dioxide as by-products. This process is commonly associated with the production of alcoholic beverages, but it has several other important uses as well.
Alcoholic Beverage Production
Alcoholic fermentation is widely used in the production of alcoholic drinks, including wine, beer, cider, and spirits. Yeast consumes sugars in the fermentation process, producing ethanol (alcohol) and carbon dioxide. This process is essential for creating the alcohol content and carbonation in these beverages.
Bread Making
Yeast used in bread dough also goes through alcoholic fermentation, producing carbon dioxide gas as a waste product. This gas forms bubbles in the dough, causing it to rise and become airy. This leavening effect is crucial in bread-making, giving the bread its fluffy texture.
Fuel and Energy
Ethanol produced through alcoholic fermentation can be used as a biofuel, providing an alternative energy source to fossil fuels. Additionally, the fermentation process itself generates heat, which can be utilized for various purposes.
Livestock Feed and Fertilizer
The by-products of ethanol fermentation, such as cereal residues, can be used as livestock feed. Additionally, the fermentation process produces fertilizer that can be used in agriculture to enhance crop growth.
Food Processing
Alcoholic fermentation is also used in food processing beyond just bread-making. For example, it is involved in the production of certain types of cheese, as well as in the preservation of some foods through a process called "lacto-fermentation."
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Frequently asked questions
Lactic acid fermentation is a metabolic process that converts glucose and other six-carbon sugars into cellular energy and the metabolite lactate. It occurs in some bacteria and animal cells, such as muscle cells, when there is a lack of oxygen.
Alcoholic fermentation is a biological process that converts sugars such as glucose, fructose, and sucrose into cellular energy, producing ethanol and carbon dioxide as by-products. It is commonly used in the production of alcoholic beverages and bread.
Lactic acid fermentation produces lactic acid and occurs in some bacteria and muscle cells, while alcoholic fermentation produces ethanol and carbon dioxide and is carried out by yeasts and some types of bacteria.
