Editing Cysteine (section)

== Industrial sources<span class="anchor" id="Dietary restrictions"></span> ==
The majority of {{sm|l}}-cysteine is obtained industrially by [[hydrolysis]] of animal materials, such as poultry feathers or hog hair. Despite widespread rumor,<ref name=Kashrut/> human hair is rarely a source material.<ref>{{cite web |url=https://www.vrg.org/vrgnews/2007jul.htm#s2 |website=vrg.org |access-date=26 August 2024 |title=VRG-News July 2007 -- the Vegetarian Resource Group }}</ref> Indeed, food additive or cosmetic product manufactures may not legally source from human hair in the European Union.<ref>{{cite web |url=http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2012:083:0001:0295:EN:PDF |title=EU Chemical Requirements |access-date=May 24, 2020 |quote=...L-cysteine hydrochloride or hydrochloride monohydrate. Human hair may not be used as a source for this substance}}</ref><ref>{{cite web |url=https://eur-lex.europa.eu/legal-content/en/TXT/?uri=CELEX%3A32009R1223 |title=Regulation (EC) No 1223/2009 of the European Parliament and of the Council of 30 November 2009 on cosmetic products |access-date=July 28, 2021 |quote=...ANNEX II LIST OF SUBSTANCES PROHIBITED IN COSMETIC PRODUCTS...416 Cells, tissues or products of human origin}}</ref>  

Some animal-originating sources of {{sm|l}}-cysteine as a food additive contravene kosher, halal, vegan, or vegetarian diets.<ref name=Kashrut>See, e.g., {{cite news|title=Like mountains hanging by a hair: Kosher issues in L-cysteine (Commentary on Chagiga I:8)|first=Zushe&nbsp;Yosef|last=Blech|work=MK News and Views|volume=IV|issue=6|date=May 2003|publisher=[[Montreal Kosher]]|via=kashrut.com|url=http://www.kashrut.com/articles/L_cysteine/}}  Rabbi Blech does not address hog hair-derived cysteine, which is almost certainly ''[[treyf]]''.</ref> To avoid this problem, synthetic {{sm|l}}-cysteine, compliant with Jewish [[kosher]] and Muslim [[halal]] laws, is also available, albeit at a higher price.<ref>{{Cite web |url= http://www.vrg.org/nutshell/faqingredients.htm#cystine |title= Questions About Food Ingredients: What is L-cysteine/cysteine/cystine? |publisher= Vegetarian Resource Group }}</ref> The typical synthetic route involves fermentation with an artificial ''[[Escherichia coli|E.&nbsp;coli]]'' strain.<ref name=Ullmann/> 

Alternatively, [[Evonik]] (formerly Degussa) introduced a route from substituted [[thiazoline]]s.<ref name="Martens">{{cite journal |last1=Martens |first1=Jürgen |author-link2=Heribert Offermanns |last2=Offermanns |first2=Heribert |last3=Scherberich |first3=Paul |year=1981 |title=Facile Synthesis of Racemic Cysteine |journal=Angewandte Chemie International Edition in English |volume=20 |issue=8 |pages=668 |doi=10.1002/anie.198106681}}</ref> ''Pseudomonas thiazolinophilum'' hydrolyzes racemic 2{{nbh}}amino-Δ<sup>2</sup>{{nbh}}thiazoline-4{{nbh}}carboxylic acid to {{sm|l}}{{nbh}}cysteine.<ref name=Ullmann>{{cite book |doi=10.1002/14356007.a02_057.pub2 |chapter=Amino Acids |title=Ullmann's Encyclopedia of Industrial Chemistry |year=2007 |last1=Drauz |first1=Karlheinz |last2=Grayson |first2=Ian |last3=Kleemann |first3=Axel |last4=Krimmer |first4=Hans-Peter |last5=Leuchtenberger |first5=Wolfgang |last6=Weckbecker |first6=Christoph |isbn=978-3-527-30673-2}}</ref>