Lactobacillus bulgaricus
Encyclopedia
Lactobacillus delbrueckii subspecies bulgaricus (until 1984 known as Lactobacillus bulgaricus) is one of several bacteria
used for the production of yogurt. It is also found in other naturally fermented products. First identified in 1905 by the Bulgarian doctor Stamen Grigorov
, the bacterium feeds on lactose
to produce lactic acid
, which is used to preserve milk.
It is a Gram-positive
rod that may appear long and filamentous. It is also non-motile, and it does not form spores. This bacterium is regarded as aciduric or acidophilic, since it requires a low pH (around 5.4-4.6) to grow effectively. The bacterium has complex nutritional requirements, including the inability to ferment any sugar except lactose.
as a starter for making yogurt. The two species work in synergy, with L.d. bulgaricus producing amino acids from milk proteins, which are then used by S.s. thermophilus. Both species produce lactic acid
, which gives yogurt its tart flavor and acts as a preservative. The resulting decrease in pH also partially coagulates the milk proteins, such as casein, resulting in yogurt's thickness. While fermenting milk, L.d. bulgaricus produces acetaldehyde
, one of the main yogurt aroma components. Some strains of L.d. bulgaricus also produce bacteriocin
s, which kill undesired bacteria in vitro.
It is often helpful to sufferers of lactose intolerance
, whose digestive systems lack the enzyme
s to break down lactose to simpler sugars.
Some of the biggest importers of the bacterium are Japan
, the USA
and the EU
.
, who named it Bacillus bulgaricus.
Ilya Metchnikoff, a professor at the Pasteur Institute
in Paris, researched the relationship between the longevity of Bulgarians
and their consumption of yogurt. He had the idea that aging is caused by putrefactive activity, or proteolysis
, by microbes that produce toxic substances in the intestine.
Proteolytic bacteria such as clostridia
, which are part of the normal intestinal flora, produce toxic substances including phenols
, ammonia
and indols by digestion of protein
s. These compounds are responsible for what Metchnikoff called intestinal auto-intoxication, which, according to him, was the cause of the physical changes associated with old age. It was already known at that time that fermentation with lactic acid bacteria
inhibits the deterioration of milk because of its low pH
.
Metchnikoff's research had also noted that, in Europe, Bulgaria and the Russian steppes, some rural populations who had consumed milk fermented with lactic acid bacteria lived relatively long lives. Based on these data Metchnikoff proposed that consumption of fermented milk would seed the intestine with harmless lactic acid bacteria, which would increase intestinal acidity and thus suppress the growth of proteolytic bacteria.
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
used for the production of yogurt. It is also found in other naturally fermented products. First identified in 1905 by the Bulgarian doctor Stamen Grigorov
Stamen Grigorov
Stamen Grigorov was a prominent Bulgarian physician and microbilogist.Stamen Grigorov was born in the village of Studen Izvor , Tran Region, Bulgaria. He completed his secondary education in natural sciences in Montpellier, France and medical science in Geneva, Switzerland. In 1905, at the age of...
, the bacterium feeds on lactose
Lactose
Lactose is a disaccharide sugar that is found most notably in milk and is formed from galactose and glucose. Lactose makes up around 2~8% of milk , although the amount varies among species and individuals. It is extracted from sweet or sour whey. The name comes from or , the Latin word for milk,...
to produce lactic acid
Lactic acid
Lactic acid, also known as milk acid, is a chemical compound that plays a role in various biochemical processes and was first isolated in 1780 by the Swedish chemist Carl Wilhelm Scheele. Lactic acid is a carboxylic acid with the chemical formula C3H6O3...
, which is used to preserve milk.
It is a Gram-positive
Gram-positive
Gram-positive bacteria are those that are stained dark blue or violet by Gram staining. This is in contrast to Gram-negative bacteria, which cannot retain the crystal violet stain, instead taking up the counterstain and appearing red or pink...
rod that may appear long and filamentous. It is also non-motile, and it does not form spores. This bacterium is regarded as aciduric or acidophilic, since it requires a low pH (around 5.4-4.6) to grow effectively. The bacterium has complex nutritional requirements, including the inability to ferment any sugar except lactose.
Use in industry
Lactobacillus delbrueckii subsp. bulgaricus is commonly used alongside Streptococcus salivarius subsp. thermophilusStreptococcus salivarius subsp. thermophilus
Streptococcus salivarius subsp. thermophilus is a Gram-positive bacteria and a homofermentative facultative anaerobe, of the viridans group. It tests negative for cytochrome, oxidase and catalase, and positive for alpha-hemolytic activity...
as a starter for making yogurt. The two species work in synergy, with L.d. bulgaricus producing amino acids from milk proteins, which are then used by S.s. thermophilus. Both species produce lactic acid
Lactic acid
Lactic acid, also known as milk acid, is a chemical compound that plays a role in various biochemical processes and was first isolated in 1780 by the Swedish chemist Carl Wilhelm Scheele. Lactic acid is a carboxylic acid with the chemical formula C3H6O3...
, which gives yogurt its tart flavor and acts as a preservative. The resulting decrease in pH also partially coagulates the milk proteins, such as casein, resulting in yogurt's thickness. While fermenting milk, L.d. bulgaricus produces acetaldehyde
Acetaldehyde
Acetaldehyde is an organic chemical compound with the formula CH3CHO or MeCHO. It is one of the most important aldehydes, occurring widely in nature and being produced on a large scale industrially. Acetaldehyde occurs naturally in coffee, bread, and ripe fruit, and is produced by plants as part...
, one of the main yogurt aroma components. Some strains of L.d. bulgaricus also produce bacteriocin
Bacteriocin
Bacteriocins are proteinaceous toxins produced by bacteria to inhibit the growth of similar or closely related bacterial strain. They are typically considered to be narrow spectrum antibiotics, though this has been debated...
s, which kill undesired bacteria in vitro.
It is often helpful to sufferers of lactose intolerance
Lactose intolerance
Lactose intolerance, also called lactase deficiency or hypolactasia, is the inability to digest and metabolize lactose, a sugar found in milk...
, whose digestive systems lack the enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s to break down lactose to simpler sugars.
Some of the biggest importers of the bacterium are Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, the USA
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and the EU
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...
.
History
Lactobacillus delbrueckii subsp. bulgaricus was first identified in 1905 by Stamen GrigorovStamen Grigorov
Stamen Grigorov was a prominent Bulgarian physician and microbilogist.Stamen Grigorov was born in the village of Studen Izvor , Tran Region, Bulgaria. He completed his secondary education in natural sciences in Montpellier, France and medical science in Geneva, Switzerland. In 1905, at the age of...
, who named it Bacillus bulgaricus.
Ilya Metchnikoff, a professor at the Pasteur Institute
Pasteur Institute
The Pasteur Institute is a French non-profit private foundation dedicated to the study of biology, micro-organisms, diseases, and vaccines. It is named after Louis Pasteur, who made some of the greatest breakthroughs in modern medicine at the time, including pasteurization and vaccines for anthrax...
in Paris, researched the relationship between the longevity of Bulgarians
Bulgarians
The Bulgarians are a South Slavic nation and ethnic group native to Bulgaria and neighbouring regions. Emigration has resulted in immigrant communities in a number of other countries.-History and ethnogenesis:...
and their consumption of yogurt. He had the idea that aging is caused by putrefactive activity, or proteolysis
Proteolysis
Proteolysis is the directed degradation of proteins by cellular enzymes called proteases or by intramolecular digestion.-Purposes:Proteolysis is used by the cell for several purposes...
, by microbes that produce toxic substances in the intestine.
Proteolytic bacteria such as clostridia
Clostridia
The Clostridia are a class of Firmicutes, including Clostridium and other similar genera. They are distinguished from the Bacilli by lacking aerobic respiration. They are obligate anaerobes and oxygen is toxic to them. Species of the genus Clostridium are all Gram-positive and have the ability to...
, which are part of the normal intestinal flora, produce toxic substances including phenols
Phenols
In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of a hydroxyl group bonded directly to an aromatic hydrocarbon group...
, ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
and indols by digestion of protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s. These compounds are responsible for what Metchnikoff called intestinal auto-intoxication, which, according to him, was the cause of the physical changes associated with old age. It was already known at that time that fermentation with lactic acid bacteria
Lactic acid bacteria
The lactic acid bacteria comprise a clade of Gram-positive, low-GC, acid-tolerant, generally non-sporulating, non-respiring rod or cocci that are associated by their common metabolic and physiological characteristics. These bacteria, usually found in decomposing plants and lactic products, produce...
inhibits the deterioration of milk because of its low pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
.
Metchnikoff's research had also noted that, in Europe, Bulgaria and the Russian steppes, some rural populations who had consumed milk fermented with lactic acid bacteria lived relatively long lives. Based on these data Metchnikoff proposed that consumption of fermented milk would seed the intestine with harmless lactic acid bacteria, which would increase intestinal acidity and thus suppress the growth of proteolytic bacteria.