L-Cysteine HCl Monohydrate
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 hydrochloride monohydrate |
|---|---|
| Chemical class | Hydrated hydrochloride salt of a sulphur-containing amino acid |
| CAS | 7048-04-6 (HCl monohydrate) · 52-89-1 (anhydrous HCl) · 52-90-4 (free base) |
| Molecular weight | 175.63 g/mol (free base 121.16) |
| Free base equivalence | 69.0% L-cysteine by weight · chloride ~20.2% · water ~10.3% |
| Solution pH | Approx. 1.5–2.0 at 10% — strongly acidic |
| Claim strength | High for the oxidation-stability and dough-conditioning chemistry |
| Buy from Herbuno | L-Cysteine HCl Monohydrate Powder · L-Cysteine 99% Powder (free base) |
| 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, because cystine — the oxidised dimer of cysteine — was first isolated from urinary calculi by William Prout in 1810. Cysteine itself is the reduced monomer, carrying a free thiol group, and that thiol is the source of both its biological importance and its handling difficulty. The hydrochloride monohydrate is the dominant commercial form precisely because the free thiol is unstable in the free base.
Why the salt exists: Free L-cysteine oxidises readily to L-cystine, the disulphide dimer, on exposure to air, moisture or trace metal ions, and the oxidation accelerates sharply at neutral and alkaline pH. Cystine is far less soluble than cysteine and is not functionally interchangeable with it. Converting to the hydrochloride drops a 10% solution to pH 1.5 to 2.0, where thiol oxidation is strongly suppressed, and the crystalline salt is substantially more stable in storage than the free base. The monohydrate is the stable crystalline hydrate and is what the pharmacopoeias specify.
Research and application trajectory: Cysteine's dominant industrial application is not nutritional but functional: as a reducing agent it cleaves disulphide bonds in wheat gluten, relaxing the dough and reducing mixing time, which is why L-cysteine HCl is approved as food additive E920 and is used across commercial baking. Nutritionally, cysteine is the rate-limiting substrate for glutathione synthesis, which is the basis of most supplement interest, though N-acetyl-L-cysteine is the more commonly used delivery form for that purpose.
Commercial source: Historically L-cysteine was obtained by acid hydrolysis of keratin from human hair or poultry feathers, which remains a live sourcing concern for vegetarian, vegan, kosher and halal certification and is worth verifying explicitly rather than assuming. Fermentation routes using engineered Escherichia coli are now established and are the appropriate specification for certified applications. The production route must be named on the certificate.
Evidence for L-Cysteine HCl Monohydrate Applications
The conversion factor is lower than other amino acid hydrochlorides because of the water of hydration, and it is frequently miscalculated. L-cysteine HCl monohydrate is 175.63 g/mol against the free base's 121.16, so 1 gram delivers 690 milligrams of cysteine, 202 milligrams of chloride and 103 milligrams of water. The anhydrous hydrochloride, a separate CAS number at 157.62 g/mol, delivers 769 milligrams. Specifying "L-cysteine HCl" without stating hydration state leaves an 11% ambiguity, which is a distinct error from the salt-versus-free-base ambiguity and is often made at the same time. Claim strength: High.
Oxidation resistance is the salt's primary functional justification and it is pH-dependent rather than intrinsic. The free thiol oxidises to the cystine disulphide on exposure to air, moisture or trace copper and iron, and the rate rises steeply above pH 5. At the pH 1.5 to 2.0 a 10% solution of the hydrochloride produces, oxidation is strongly suppressed. The practical consequence is that the protection travels with the acidity: dissolve the hydrochloride into a neutral matrix and the pH advantage is lost, and oxidation proceeds as it would for the free base. Chelating agents and oxygen exclusion are the complementary controls. Claim strength: High.
The dough conditioning function is well established and is the largest-volume use. Cysteine's thiol reduces disulphide crosslinks in the gluten network, relaxing the dough, shortening mixing time and improving machinability, which is the basis of its approval as E920. Typical bakery inclusion is in the range of 10 to 90 parts per million on flour weight, far below nutritional doses. The mechanism is chemical reduction rather than enzymatic, so it is dose-responsive and predictable, and overdosing produces slack, sticky dough. This is a functional additive application with a long industrial record. Claim strength: High.
Cysteine is the rate-limiting substrate for glutathione synthesis, which is the mechanistic basis for supplement interest, though the delivery question is unresolved. Glutathione is a tripeptide of glutamate, cysteine and glycine, and cysteine availability is generally the constraint on its synthesis. Supplying cysteine therefore has a sound rationale. In practice N-acetyl-L-cysteine is the more commonly used form, on the argument that the acetyl group protects the thiol through absorption, and most of the clinical glutathione literature uses NAC rather than cysteine or its hydrochloride. Direct trials comparing the forms are limited. Claim strength: Moderate for the biochemistry, Emerging for the delivery comparison.
The keratin sourcing question is a genuine certification issue, not a historical footnote. L-cysteine has long been produced by acid hydrolysis of keratin, with human hair and poultry feathers as the feedstocks, and material from those routes remains in the market. For vegetarian, vegan, kosher or halal positioning the production route must be verified on the certificate rather than assumed from the supplier's general certifications, since a certification body may have assessed the facility without the specific feedstock being in scope. Fermentation-derived material from engineered E. coli is the appropriate specification. Claim strength: High.
Tolerability is acceptable but the acidity and the odour are real formulation constraints. L-cysteine HCl monohydrate in solution is strongly acidic and can be irritating to oral and gastric mucosa at supplemental concentrations, so buffering or encapsulation is usually required for oral formats above functional-additive levels. The sulphurous odour, characteristic of reduced thiols, is pronounced and intensifies on oxidation. At food-additive inclusion levels neither is an issue; at nutritional doses both require active formulation work. Claim strength: Moderate.
Sourcing L-cysteine HCl monohydrate from Herbuno. We supply the hydrochloride monohydrate and the free base.
Two things to settle on the specification. State the hydration state explicitly — monohydrate and anhydrous hydrochloride are separate CAS numbers with an 11% difference in cysteine content. And if the application requires vegetarian, vegan, kosher or halal certification, require the production route to be named: keratin-hydrolysate material is still traded, and fermentation-derived material is the correct specification. All lots ship with CoA and MSDS; request a quotation for pilot or bulk volumes.
Dosage & Formulator Specification
Three conversion factors apply in this category and confusing them is the commonest error. The monohydrate hydrochloride at 175.63 g/mol gives 69.0% cysteine; the anhydrous hydrochloride at 157.62 gives 76.9%; the free base is 100%. For a 500 milligram cysteine target: 725 milligrams of monohydrate, 650 milligrams of anhydrous salt, or 500 milligrams of free base. Write the hydration state and the declaration basis into the specification, because the two ambiguities compound and a 500 milligram claim can be met by anything from 500 to 725 milligrams of powder depending on how it is read.
Dose ranges differ by an order of magnitude between the two main applications, which is worth stating explicitly to avoid cross-contamination of specifications. As a dough conditioner the inclusion is 10 to 90 parts per million on flour weight — milligrams per kilogram. As a nutritional ingredient, doses in the glutathione literature are in the hundreds of milligrams to grams, though most of that literature uses N-acetyl-L-cysteine rather than cysteine itself. A supplier quotation written against one application is not transferable to the other without revisiting the specification.
Handling is dominated by thiol chemistry and the acidity. The monohydrate is freely soluble in water at above 25 grams per 100 millilitres, giving strongly acidic solutions at pH 1.5 to 2.0. Store cool, dry and sealed with oxygen exclusion where possible, and keep away from trace copper and iron, which catalyse thiol oxidation to cystine. The powder is mildly hygroscopic. The sulphurous odour is pronounced and intensifies with age and exposure, so a lot with a noticeably stronger odour than reference material warrants a cystine check before use.
Formulation into neutral matrices requires explicit stabilisation, because the salt's protection is pH-derived and does not survive dilution into a buffered system. In a near-neutral beverage or a chewable, a dissolved cysteine hydrochloride is no better protected than the free base. The available controls are chelating the catalytic metals, excluding oxygen through packaging and headspace management, maintaining the lowest acceptable pH, co-formulating with ascorbate as a competing reductant, or encapsulating. Where none of these is practical, N-acetyl-L-cysteine is the more robust choice and the honest recommendation.
For analytical control, specify identity and assay per USP, EP or JP for the hydrate in question, with optical rotation confirming L-configuration, chloride content confirming stoichiometry, and water content confirming hydration state. Critically, specify L-cystine as a limit test: it is the oxidation product, it is the direct indicator of material quality and storage history, and a standard cysteine assay may not resolve it. Standard coverage includes heavy metals — with particular attention to copper and iron given their catalytic role — residual solvents, microbiological limits, loss on drying and sulphated ash.
On production route, require it in writing. Keratin hydrolysis from human hair or poultry feathers remains an active commercial route for L-cysteine, and material from it is not acceptable for vegetarian, vegan, kosher or halal positioning. A supplier's general certification portfolio does not by itself establish the feedstock for a given lot, so the route should be named on the certificate and, for a new supplier, confirmed by audit or at least by a specific written declaration. Fermentation-derived material from engineered Escherichia coli on a carbohydrate substrate is the appropriate specification for certified applications, and the organism and substrate should both be stated.
Frequently Asked Questions — L-Cysteine HCl Monohydrate
How much cysteine does the monohydrate deliver?
69.0% by weight — 175.63 g/mol against 121.16 free base, with 202 mg chloride and 103 mg water per gram. The anhydrous hydrochloride is a different CAS number at 157.62 g/mol and gives 76.9%. Specifying "L-cysteine HCl" without the hydration state leaves an 11% ambiguity on top of the salt-versus-free-base one.
Why the hydrochloride rather than free cysteine?
Oxidation. The free thiol converts to the cystine disulphide on exposure to air, moisture or trace copper and iron, and the rate rises steeply above pH 5. A 10% solution of the hydrochloride sits at pH 1.5 to 2.0, where oxidation is strongly suppressed, and the crystalline salt stores far better than the free base.
Does the salt protect cysteine in a neutral product?
No — the protection is pH-derived and does not survive dilution into a buffered matrix. In a near-neutral beverage, dissolved cysteine hydrochloride is no better protected than the free base. Chelate the catalytic metals, exclude oxygen, keep pH as low as acceptable, or encapsulate. Where none works, N-acetyl-L-cysteine is the more robust choice.
What is E920?
L-cysteine HCl as a dough conditioner. The thiol reduces disulphide crosslinks in gluten, relaxing the dough and shortening mixing time. Inclusion is 10 to 90 ppm on flour weight — milligrams per kilogram, orders of magnitude below nutritional doses. Overdosing gives slack, sticky dough. A quotation written for this application does not transfer to a nutritional one.
Is cysteine made from hair?
It can be. Acid hydrolysis of keratin from human hair or poultry feathers is a long-standing commercial route and material from it is still traded. For vegetarian, vegan, kosher or halal positioning, require the production route named on the certificate — a supplier's general certifications do not establish the feedstock for a given lot. Specify fermentation-derived.
What should I specify beyond assay?
L-cystine as a limit test. It is the oxidation product and the direct indicator of material quality and storage history, and a standard cysteine assay may not resolve it. Also water content to confirm hydration state, chloride to confirm stoichiometry, and copper and iron specifically given their catalytic role in thiol oxidation.