Propionibacterium freudenreichii
Encyclopedia
Propionibacterium freudenreichii is a Gram-positive
, nonmotile bacterium that plays an important role in the creation of Emmental cheese, and to some extent, leerdammer
. Its concentration in Swiss-type cheeses
is higher than in any other cheese. Propionibacteria are commonly found in milk and dairy products, though they have also been extracted from soil. P. freudenreichii has a circular chromosome about 2.5 Mb long. When Emmental cheese is being produced, P. freudenreichii ferments lactate to form acetate
, propionate
and carbon dioxide
(3 C3H6O3 → 2 C2H5CO2 + C2H3O2 + CO2).
The products of this fermentation
contribute to the nutty and sweet flavors of the cheese, and the carbon dioxide byproduct is responsible for forming the holes, or "eyes
" in the cheese. Cheesemakers control the size of the holes by changing the acidity, temperature, and curing time of the mixture. An estimated one billion living cells of P. freudenreichii are present in one gram of Emmental. In contrast to most lactic acid bacteria, this bacterium mainly breaks down lipids, forming free fatty acids. Recent research has focused on possible benefits incurred from consuming P. freudenreichii, which are thought to cleanse the gastrointestinal tract . It has also been suggested P. freudenreichii can lower the incidence of colon cancer. This mutualistic relationship is unusual in propionibacteria, which are largely commensal.
The performance and growth of P. freudenreichii is highly dependent on the presence of Lactobacillus helveticus
, which provides essential amino acids. The degradation of L. helvecticus releases a variety of amino acids and peptide
s. While P. freudenreichii has been found to grow even in the absence of L. helvecticus, some strains of the bacteria were observed lysing in the absence of glutamine
, lysine
or tyrosine
. It has been suggested the autolysis of P. freudenreichii contributes further to the flavor of the Emmental cheese. The conditions leading to the autolysis of this bacterium are not well known.
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...
, nonmotile bacterium that plays an important role in the creation of Emmental cheese, and to some extent, leerdammer
Leerdammer
Leerdammer is a Dutch semi-hard cheese made from cow's milk. It has an aging time of around 3–12 months.It has a creamy white texture and was made to be similar in appearance and flavor to Emmental, but it is rounder in taste. It has a sweet and somewhat nutty flavour that becomes more pronounced...
. Its concentration in Swiss-type cheeses
Swiss cheese
Swiss cheese is a generic name in North America for several related varieties of cheese which resemble the Swiss Emmental. Some types of Swiss cheese have a distinctive appearance, as the blocks of the cheese are riddled with holes known as "eyes". Swiss cheese has a piquant, but not very sharp,...
is higher than in any other cheese. Propionibacteria are commonly found in milk and dairy products, though they have also been extracted from soil. P. freudenreichii has a circular chromosome about 2.5 Mb long. When Emmental cheese is being produced, P. freudenreichii ferments lactate to form acetate
Acetate
An acetate is a derivative of acetic acid. This term includes salts and esters, as well as the anion found in solution. Most of the approximately 5 billion kilograms of acetic acid produced annually in industry are used in the production of acetates, which usually take the form of polymers. In...
, propionate
Propionate
The propanoate or propionate ion is C2H5COO− .A propanoic or propionic compound is a salt or ester of propanoic acid....
and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
(3 C3H6O3 → 2 C2H5CO2 + C2H3O2 + CO2).
The products of this fermentation
Fermentation (food)
Fermentation in food processing typically is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions. Fermentation in simple terms is the chemical conversion of sugars into ethanol...
contribute to the nutty and sweet flavors of the cheese, and the carbon dioxide byproduct is responsible for forming the holes, or "eyes
Eyes (cheese)
Eyes are the round holes that are a characteristic feature of Swiss-type cheese and some Dutch-type cheeses. They are bubbles of carbon dioxide gas that is produced by bacteria in the cheese....
" in the cheese. Cheesemakers control the size of the holes by changing the acidity, temperature, and curing time of the mixture. An estimated one billion living cells of P. freudenreichii are present in one gram of Emmental. In contrast to most lactic acid bacteria, this bacterium mainly breaks down lipids, forming free fatty acids. Recent research has focused on possible benefits incurred from consuming P. freudenreichii, which are thought to cleanse the gastrointestinal tract . It has also been suggested P. freudenreichii can lower the incidence of colon cancer. This mutualistic relationship is unusual in propionibacteria, which are largely commensal.
The performance and growth of P. freudenreichii is highly dependent on the presence of Lactobacillus helveticus
Lactobacillus helveticus
Lactobacillus helveticus is a lactic-acid producing rod shaped bacterium of the genus Lactobacillus. It is most commonly used in the production of American Swiss cheese and Emmental cheese but is also sometimes used in making other styles of cheese, such as Cheddar, Parmesan, romano, provolone,...
, which provides essential amino acids. The degradation of L. helvecticus releases a variety of amino acids and peptide
Peptide
Peptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...
s. While P. freudenreichii has been found to grow even in the absence of L. helvecticus, some strains of the bacteria were observed lysing in the absence of glutamine
Glutamine
Glutamine is one of the 20 amino acids encoded by the standard genetic code. It is not recognized as an essential amino acid but may become conditionally essential in certain situations, including intensive athletic training or certain gastrointestinal disorders...
, lysine
Lysine
Lysine is an α-amino acid with the chemical formula HO2CCH4NH2. It is an essential amino acid, which means that the human body cannot synthesize it. Its codons are AAA and AAG....
or tyrosine
Tyrosine
Tyrosine or 4-hydroxyphenylalanine, is one of the 22 amino acids that are used by cells to synthesize proteins. Its codons are UAC and UAU. It is a non-essential amino acid with a polar side group...
. It has been suggested the autolysis of P. freudenreichii contributes further to the flavor of the Emmental cheese. The conditions leading to the autolysis of this bacterium are not well known.