L-Cysteine
Compiled from published pharmacological and botanical literature. Not independently verified by Herbuno. Spotted an error or have a correction? Flag it below →
| Compound | L-Cysteine |
|---|---|
| Chemical class | Conditionally essential sulphur-containing α-amino acid — thiol side chain |
| CAS | 52-90-4 (free base) · 7048-04-6 (hydrochloride monohydrate) |
| Primary source | Microbial fermentation; historically by keratin hydrolysis, now largely superseded |
| Key applications | Glutathione synthesis, disulphide bond formation, taurine and coenzyme A precursor, dough conditioning |
| Claim strength | High as the limiting substrate for glutathione; Moderate for supplementation outcomes |
| Typical form | Free base or hydrochloride monohydrate at 99%; also as N-acetyl-L-cysteine |
| Buy from Herbuno | L-Cysteine 99% Powder · L-Cysteine HCl Monohydrate · N-Acetyl-L-Cysteine EP · N-Acetyl-L-Cysteine USP |
| Origin | Processed / Sourced from India |
| MOQ | R&D 100 g / 250 g (subject to stock) · Pilot batch 1–5 kg · Bulk 10 kg, 25 kg and above |
| Lead Time | Dispatch within 72 hrs from stock · fresh-batch production (typically 50 kg+): 10 working days |
| Documentation | CoA & MSDS standard with every lot |
Name origin: From the Greek kystis, bladder — cystine, the oxidised dimer, was isolated from a urinary calculus by William Wollaston in 1810 and named for its source. Cysteine is the reduced monomer, identified later. The relationship matters practically: two cysteine molecules spontaneously oxidise to one cystine via a disulphide bond, and this happens readily in air and in solution.
Discovery and production history: Cysteine's production history is unusually relevant to its commercial positioning. For most of the twentieth century it was manufactured by acid hydrolysis of keratin — human hair, poultry feathers, hooves — which remains a live concern for vegetarian, vegan, kosher and halal certification. Fermentation routes using engineered Escherichia coli displaced much of that capacity from the 1990s onward, and fermentation-derived material is now the standard for supplement and food applications where provenance matters. A buyer who does not specify the route may receive either.
Research trajectory: Cysteine's significance rests on glutathione. Of the three amino acids forming glutathione — glutamate, cysteine, glycine — cysteine is the rate-limiting one, because its free concentration is kept low by the cell to avoid thiol reactivity. This made cysteine delivery the obvious target for raising glutathione, and because free cysteine is unstable and poorly tolerated, N-acetylcysteine became the clinical vehicle. NAC has a substantial literature of its own as a mucolytic and as the antidote for paracetamol overdose.
Commercial source: Fermentation-derived L-cysteine is supplied as the free base or as the hydrochloride monohydrate, which is more stable and easier to handle. N-acetyl-L-cysteine is manufactured by acetylation and is available to EP and USP pharmacopoeial standards, which is a meaningful distinction for regulated applications. The production route determines certification eligibility more than any other variable in this category.
Evidence for L-Cysteine Applications
Cysteine as the limiting substrate for glutathione is well established and is the strongest claim available. Glutathione is synthesised from glutamate, cysteine and glycine, and cellular cysteine availability constrains the rate because free cysteine is maintained at low concentration to limit thiol reactivity and autoxidation. Supplying cysteine, usually as NAC, raises glutathione synthesis in depleted states. The practical consequence is that glutathione supplementation itself is a poor strategy — oral glutathione is substantially degraded before absorption — while cysteine delivery works upstream of the constraint. Claim strength: High.
Free cysteine is a difficult molecule to deliver, which is why NAC dominates. The thiol group oxidises readily to cystine in air, in solution and during processing, and cystine is far less soluble and not equivalent in delivering cysteine to tissue. Free cysteine also has poor oral tolerability at higher doses and a pronounced sulphurous taste. N-acetylation protects the thiol, substantially improves stability and tolerability, and the acetyl group is removed in vivo. For most formulations, NAC is the practical route, and free cysteine makes sense mainly where the acetylated form is unsuitable for regulatory or label reasons. Claim strength: High.
NAC's clinical evidence is strong in specific indications and weaker in general wellness positioning. It is the established antidote for paracetamol hepatotoxicity, a role in which it is unambiguous and life-saving, and it has a long history as a mucolytic in chronic bronchitis and cystic fibrosis. Trials in psychiatric conditions, particularly trichotillomania and some obsessive-compulsive spectrum disorders, have shown signals. General antioxidant and detoxification positioning extends well beyond those indications on the strength of the glutathione mechanism rather than on outcome data. Claim strength: High within indication, Emerging outside it.
Ageing and glutathione decline is an active and reasonably promising area. Glutathione concentrations fall with age, and work in older adults has found that combined glycine and cysteine supplementation restored glutathione synthesis rates and improved several markers of oxidative stress and mitochondrial function more than either alone. This is a more specific and better-grounded claim than general antioxidant marketing, and it points toward combination formulation rather than cysteine in isolation. Claim strength: Moderate.
The food application is large and often overlooked by supplement formulators. L-cysteine is widely used as a dough conditioner, where its thiol group cleaves disulphide bonds in gluten, reducing mixing time and improving extensibility. This is a functional food additive use at low inclusion, not a nutritional one, and it is the main reason keratin-derived cysteine remains in circulation. For any product carrying vegetarian, vegan, kosher or halal claims, the production route must be specified and documented rather than assumed. Claim strength: High.
Safety is good with specific cautions worth carrying. NAC at 600 to 1,800 milligrams daily is well tolerated, with gastrointestinal upset the usual complaint at higher doses. There is a regulatory wrinkle in some markets: NAC's status as a supplement ingredient has been contested in the US because of its prior approval as a drug, and the position has shifted more than once, so market-specific confirmation is advisable rather than optional. Free cysteine at high doses is less well tolerated than NAC. Claim strength: Moderate.
Sourcing L-cysteine from Herbuno. We supply fermentation-derived L-cysteine as the free base and as the hydrochloride monohydrate, plus N-acetyl-L-cysteine to EP and USP standards.
Specify the production route explicitly if you carry vegetarian, vegan, kosher or halal claims — keratin-derived cysteine is still in circulation and a buyer who does not specify may receive it. All lots ship with CoA and MSDS as standard; request a quotation for pilot or bulk volumes.
Dosage & Formulator Specification
L-cysteine hydrochloride monohydrate is roughly 69% cysteine by weight, so the salt and the amino acid differ substantially — more than for most amino acids — and dosing on salt weight will under-deliver by nearly a third. N-acetyl-L-cysteine is about 74% cysteine by weight. Clinical NAC doses run 600 to 1,800 milligrams daily, commonly 600 milligrams twice daily. Where a formulation targets glutathione support, the evidence points toward combining a cysteine source with glycine rather than using cysteine alone.
Form selection is largely settled by stability. Free cysteine oxidises to cystine on exposure to air, in solution and under processing heat, and cystine is poorly soluble and does not deliver equivalently. For capsules and dry blends with good moisture control, free cysteine or the hydrochloride is workable; for anything aqueous, extended shelf life, or thermally processed, NAC is the practical answer. Where free cysteine must be used, antioxidant protection, oxygen-barrier packaging and realistic shelf-life claims are necessary rather than optional.
Sensory impact is significant and should be planned for, not discovered. Sulphur-containing amino acids carry a distinct eggy, sulphurous note that becomes prominent at the doses used and is difficult to mask fully. It intensifies as oxidation proceeds, so a product that was acceptable at manufacture can become objectionable over shelf life. Capsules sidestep the problem entirely and are the usual format for this reason. Cysteine is also reactive toward aldehyde flavour compounds, which can both degrade the flavour system and generate off-notes.
For analytical control, specify identity and assay by HPLC or ion-exchange chromatography with optical rotation confirming L-configuration, and require cystine as a specified impurity, since it is the oxidation marker that reveals how the material has been stored and handled. State clearly whether the specification is for free cysteine, the hydrochloride or NAC. For NAC in regulated applications, specify the pharmacopoeial standard, EP or USP. The certificate should name the production route and organism, which is what vegan, kosher and halal documentation rests on. Fermentation-derived material does not require phytosanitary certification.
A note on pharmacopoeial grade, which matters more here than for most amino acids. NAC is supplied to EP and USP standards as well as food grade, and the pharmacopoeial monographs carry tighter impurity and identity requirements along with a documented manufacturing standard. For supplement applications food grade is often adequate, but where a product is positioned on clinical parity, sold into a regulated channel, or exported to a market where NAC's supplement status is contested, the pharmacopoeial grade is the defensible choice. Decide this at specification rather than discovering it during a registration review, since switching grade late usually means requalifying the supplier.
Frequently Asked Questions — L-Cysteine
Why supplement cysteine rather than glutathione?
Because cysteine is the rate-limiting substrate and oral glutathione is largely degraded before absorption. Glutathione is built from glutamate, cysteine and glycine, and cellular cysteine availability constrains the rate since free cysteine is kept low to limit thiol reactivity. Supplying cysteine works upstream of the constraint; supplying glutathione mostly does not survive the gut.
Should I use NAC or free cysteine?
NAC for most applications. Free cysteine's thiol oxidises to cystine in air, in solution and under heat, and cystine is poorly soluble and not equivalent. NAC protects the thiol, is better tolerated, and the acetyl group comes off in vivo. Free cysteine makes sense mainly where NAC is unsuitable for regulatory or label reasons — and its status as a supplement ingredient has been contested in some markets.
Is your cysteine made from hair or feathers?
Ours is fermentation-derived. The question is a fair one: keratin hydrolysis — human hair, poultry feathers, hooves — was the standard route for most of the twentieth century and material from it is still in circulation. If you carry vegetarian, vegan, kosher or halal claims, specify the route in writing rather than assuming.
What impurity should the certificate show?
Cystine. It is the oxidation product of cysteine and therefore tells you how the material has been stored and handled before reaching you, which an assay figure alone will not. Also state whether the specification is for free cysteine, the hydrochloride or NAC, since the cysteine fractions differ substantially — the HCl monohydrate is only about 69% cysteine.
Will it smell?
Yes. Sulphur amino acids carry an eggy, sulphurous note that is hard to mask and intensifies as oxidation proceeds, so a product acceptable at manufacture can become objectionable over shelf life. Capsules avoid the problem and are the usual format for this reason. Cysteine also reacts with aldehyde flavour compounds, degrading the flavour system.
Why source cysteine from India?
Around 80% of raw nutraceutical ingredients originate in China and a second qualified origin is increasingly a continuity requirement. For cysteine the provenance question is sharper than usual given the keratin legacy, and India has established fermentation capacity with the certification infrastructure that vegan, kosher and halal documentation requires.