Propionibacterium freudenreichii is a Gram-positive, non-motile 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. P. freudenreichii has also been suggested to possibly 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 peptides. 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. The autolysis of P. freudenreichii has been suggested to contribute further to the flavor of the Emmental cheese. The conditions leading to the autolysis of this bacterium are not well known.
- "A bacterium used in the production of Emmental." Genoscope. 16 Jan. 2008. <http://www.genoscope.cns.fr/spip/propionibacterium-freudenreichii,467.html>.
- Cousin, F.J.; et al. (2010). "Dairy propionibacteria as human probiotics: A review of recent evidence". Dairy Science and Technology. doi:10.1051/dst/2010032. ISSN 1958-5594.
- Jan, G.; et al. (2002). "Propionibacteria induce apoptosis of colorectal carcinoma cells via short-chain fatty acids acting on mitochondria". Cell Death and Differentiation 9 (2): 179–188. doi:10.1038/sj/cdd/4400935. ISSN 1350-9047. PMID 11840168.
- Lan, A.; et al. (2008). "Increased induction of apoptosis by Propionibacterium freudenreichii TL133 in colonic mucosal crypts of human microbiota-associated rats treated with 1,2-dimethylhydrazine". British Journal of Nutrition 100 (6): 1251–1259. doi:10.1017/S0007114508978284. ISSN 0007-1145. PMID 18466653.
- McCarthy, R. J. "Amino acid requirements of dairy Propionibacterium strains." Ohio State University. <http://ift.confex.com/ift/2004/techprogram/paper_26294.htm>.
- Ostlie, H.; et al. (1995). "Autolysis of Dairy Propionibacteria: Growth Studies, Peptidase Activities, and Proline Production". Journal of Dairy Science 78 (6): 1224–1237. doi:10.3168/jds.S0022-0302(95)76742-X. ISSN 0022-0302.