Flavor ingredient regulatory record
l-Cysteine
l-Cysteine is a thiol in the savory family, FEMA GRAS under FEMA number 3263 (CAS 52-90-4). Its odor is sulfurous, meaty, savory, umami.
- FEMA
- 3263
- CAS
- 52-90-4
- JECFA
- 1419
- EU FL
- 17.033
- Formula
- C3H7NO2S
- EC
- 200-158-2
GRAS status: FEMA GRAS, publication 5. Recorded by FDA in the Substances Added to Food inventory under CAS 52-90-4.
Structure
Identity
Also known as: Cysteine, L-, Half-cystine, β-Mercaptoalanine, Thioserine, L-(+)-Cysteine, Cysteine, Propanoic acid, 2-amino-3-mercapto-, (R)-, Cystein, L-Alanine, 3-mercapto-, NSC 8746, (R)-2-Amino-3-mercaptopropanoic acid, (R)-Cysteine.
Can l-Cysteine be labeled natural?
The process decides for l-Cysteine. It occurs in nature, so a natural-source, natural-process material is natural flavor in the US and synthetic l-Cysteine is artificial. The EU and UK follow the same logic without a middle class; Mercosur and Mexico label synthetic l-Cysteine identical-to-natural.
- United States
- Natural or artificial, by process
- European Union and UK
- Natural only from natural material
- Mercosur and Mexico
- Natural or identical-to-natural
How each market defines the classes: natural vs artificial flavor under 21 CFR 101.22.
Regulatory status, with citations
United States
l-Cysteine is FEMA GRAS under FEMA number 3263. It is cited in the Code of Federal Regulations at 21 CFR 184.1271 and 21 CFR 172.320.
European Union and United Kingdom
Listed on the Union List of flavouring substances as FL 17.033, Annex I Part A under Regulation (EC) 1334/2008, evaluation status approved (EFSA). The UK retains the same list.
JECFA (WHO / FAO)
JECFA number 1419, evaluated at the 63rd meeting in 2004. No safety concern at current levels of intake when used as a flavouring agent.
Other US flags
Not on the California Proposition 65 list.
TSCA Inventory status
A flavor ingredient is also an industrial chemical. l-Cysteine appears on the EPA Toxic Substances Control Act Chemical Substance Inventory under CAS 52-90-4, where EPA names it L-Cysteine.
Active in US commerce
EPA designates this substance active, so no Notice of Activity Form B is required before manufacturing. What active and inactive mean.
EPA publishes no regulatory flags on this listing. What the flags mean.
From the EPA non-confidential TSCA Inventory, July 2026 release. EPA also maintains a confidential portion it does not publish. Search the Inventory by CAS number.
Odor and taste
Odor: Sulfurous, meaty, savory, umami.
Where it is used
l-Cysteine is used in flavor enhancer, meat products, snacks and seasonings, typically as a savory note.
Structurally similar flavor ingredients
Flavor ingredients with a GRAS determination closest to l-Cysteine by structure. Whether one can replace it is a sensory and regulatory call; the reformulation tool works that through.
| Material | FEMA | Similarity | Occurrence |
|---|---|---|---|
| 3-Mercaptopropionic acid | 4587 | 90% | In nature |
| L-Threonine | 4710 | 80% | In nature |
| L-Alanine | 3818 | 80% | In nature |
| 2-Mercaptopropionic acid | 3180 | 79% | In nature |
| l-Valine | 3444 | 79% | In nature |
More thiols in this index
2-Acetyl-5-methylthiophene · 2-Isobutyl-4,6-dimethyldihydro-1,3,5-dithiazine and 4-isobutyl-2,6-dimethyldihydro-1,3,5-dithiazine · 2-Isopropyl-4,6-dimethyl and 4-Isopropyl-2,6-dimethyldihydro-1,3,5-dithiazine · 2-Ethyl-4,6-dimethyl-dihydro-1,3,5-dithiazine · Pyrrolidino-[1,2e]-4H-2,4-dimethyl-1,3,5-dithiazine · 4-Mercapto-4-methyl-2-hexanone
l-Cysteine FAQ
Is l-Cysteine on the FEMA GRAS list?
It is. FEMA number 3263 covers l-Cysteine. The Code of Federal Regulations lists it at 21 CFR 184.1271 and 21 CFR 172.320.
What is the FEMA number for l-Cysteine?
The FEMA number for l-Cysteine is 3263 and its CAS registry number is 52-90-4. Its flavor category is savory.
What is l-Cysteine used for?
l-Cysteine is described as sulfurous, meaty, savory, umami. It shows up in flavor enhancer, meat products, snacks and seasonings.
What did JECFA conclude about l-Cysteine?
JECFA evaluated l-Cysteine at the 63rd meeting in 2004 under JECFA number 1419. The panel concluded: No safety concern at current levels of intake when used as a flavouring agent.
Is l-Cysteine approved in the EU?
Yes. FL 17.033 is the Union List entry for l-Cysteine, annex I Part A, under Regulation 1334/2008, and the UK keeps the same list.
Is l-Cysteine natural or artificial?
Nature makes l-Cysteine, which is why the US label turns on process. A natural route gives natural flavor; synthesis gives artificial l-Cysteine, same molecule. The EU and UK grant the natural claim only to that natural route; Mercosur and Mexico call synthetic material identical-to-natural.
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Sources and attribution. The identity and regulatory facts on this page are taken from the FDA Substances Added to Food inventory, a US government record, which lists this substance as L-CYSTEINE under CAS 52-90-4 and carries its FEMA number, its JECFA flavor number and its 21 CFR citations. The inventory is searchable at FDA. FDA records its technical effect as dough strengthener, flavor enhancer, flavoring agent or adjuvant, flour treating agent, nutrient supplement.
A FEMA GRAS conclusion is reached by the Expert Panel of the Flavor and Extract Manufacturers Association of the United States, and the FEMA number names that conclusion. FEMA publishes its own entry for this substance in the FEMA Flavor Library, which is the authoritative record of what the Panel decided and is worth reading alongside this page.
Ambrose Compliance is not affiliated with, endorsed by, or sponsored by FEMA. FEMA and FEMA GRAS are used here as identifiers for a published regulatory determination, not as marks of any relationship between FEMA and Ambrose.
About this page. Facts come from the FDA Substances Added to Food inventory, the Code of Federal Regulations, the EPA TSCA Inventory, the EU Union List, JECFA and the Ambrose database, with FEMA's published determination cited where it applies; parts of the text are written by Ambrose AI, which can make mistakes. Check the cited source before relying on anything here. This is not regulatory or legal advice.