Editing Chymosin (section)

==Recombinant chymosin==
Because of the imperfections and scarcity of microbial and animal rennets, producers sought replacements. With the development of genetic engineering, it became possible to extract rennet-producing genes from animal stomach and insert them into certain [[bacteria]], [[fungi]] or [[yeasts]] to make them produce chymosin during fermentation.<ref name="pmid6304731">{{cite journal | vauthors = Emtage JS, Angal S, Doel MT, Harris TJ, Jenkins B, Lilley G, Lowe PA | title = Synthesis of calf prochymosin (prorennin) in Escherichia coli | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 80 | issue = 12 | pages = 3671–5 | date = June 1983 | pmid = 6304731 | pmc = 394112 | doi = 10.1073/pnas.80.12.3671 | bibcode = 1983PNAS...80.3671E | doi-access = free }}</ref><ref name="pmid6283469">{{cite journal | vauthors = Harris TJ, Lowe PA, Lyons A, Thomas PG, Eaton MA, Millican TA, Patel TP, Bose CC, Carey NH, Doel MT | display-authors = 6 | title = Molecular cloning and nucleotide sequence of cDNA coding for calf preprochymosin | journal = Nucleic Acids Research | volume = 10 | issue = 7 | pages = 2177–87 | date = April 1982 | pmid = 6283469 | pmc = 320601 | doi = 10.1093/nar/10.7.2177 }}</ref>  The genetically modified microorganism is killed after fermentation and chymosin is isolated from the fermentation broth, so that the fermentation-produced chymosin (FPC) used by cheese producers does not contain any GM component or ingredient.<ref name="GMO Database"/> FPC contains the identical chymosin as the animal source, but produced in a more efficient way. FPC products have been on the market since 1990 and are considered the ideal milk-clotting enzyme.<ref name="Law 2010 100–101">{{cite book|author = Law BA | title = Technology of Cheesemaking|year=2010|publisher= Wiley-Blackwell | location = UK | isbn = 978-1-4051-8298-0 | pages = 100–101 |url = http://eu.wiley.com/WileyCDA/WileyTitle/productCd-1405182989.html}}</ref>

FPC was the first artificially produced enzyme to be registered and allowed by the [[US Food and Drug Administration]]. In 1999, about 60% of US [[hard cheese]] was made with FPC<ref name="USDA">{{cite web |url=https://fpc.state.gov/6176.htm|title=Food Biotechnology in the United States: Science, Regulation, and Issues|publisher=U.S. Department of State|access-date=2006-08-14}}</ref> and it has up to 80% of the global market share for rennet.<ref name="pmid16537950">{{cite journal | vauthors = Johnson ME, Lucey JA | title = Major technological advances and trends in cheese | journal = Journal of Dairy Science | volume = 89 | issue = 4 | pages = 1174–8 | date = April 2006 | pmid = 16537950 | doi = 10.3168/jds.S0022-0302(06)72186-5 | doi-access = free }}</ref>

By 2008, approximately 80% to 90% of commercially made cheeses in the US and Britain were made using FPC.<ref name="GMO Database">{{cite web|url=http://www.gmo-compass.org/eng/database/enzymes/83.chymosin.html|publisher=GMO Compass|title=Chymosin|access-date=2011-03-03|url-status=dead|archive-url=https://web.archive.org/web/20150326181805/http://www.gmo-compass.org/eng/database/enzymes/83.chymosin.html|archive-date=2015-03-26}}</ref> The most widely used fermentation-produced chymosin is produced either using the fungus ''[[Aspergillus niger]]'' or using ''[[Kluyveromyces lactis]]''.

FPC contains only chymosin B,<ref>Bovine chymosins A and B differ by one amino acid residue. This is probably an alleic variant, according to Uniprot:P00794. The two isoforms have identical catalytic activity, so any improvement in the product is due to the elimination of other impurities.</ref> achieving a higher degree of purity compared with animal rennet. FPC can deliver several benefits to the cheese producer compared with animal or microbial rennet, such as higher production yield, better curd texture and reduced bitterness.<ref name="Law 2010 100–101"/>