Amino Acids & Peptides
REACH
L-cystine
CAS Number
56-89-3
EC Number
200-296-3
What is L-cystine?
L-Cystine (CAS 56-89-3), also known by its E-number E921, is the oxidized disulfide dimer of cysteine and a naturally occurring amino acid sourced from fermentation and protein hydrolysis.
Where is L-cystine used?
- Food, pharmaceutical and cosmetic manufacturing: antioxidant, dough conditioner and structural protein precursor
- Bakery: reducing agent that modifies gluten structure, improving dough extensibility and cutting mixing time in bread and crackers
- Pharmaceuticals: amino acid supplement ingredient in infusion solutions, clinical nutrition and tablets for metabolic support and recovery
- Personal care: hair treatments and keratin-based formulations, where disulfide bonding supports hair fiber repair and conditioning
- Food and beverage manufacturers use it as an approved processing aid and antioxidant stabilizer.
Good to know: Pharmaceutical-grade material is subject to stricter purity specifications. Origin documentation is increasingly relevant to buyer qualification and quality assurance.
Commercial specifications
- Bulk quantities from fermentation-derived or hydrolysis-derived sources
Other Names (Synonyms)
β,β'-dithiodialanine|L-Dicysteine|L-alpha-Diamino-beta-dithiolactic acid|(R,R)-3,3'-dithiobis(2-aminopropanoic acid)|(-)-cystine|(2R,2'R)-3,3'-disulfanediylbis(2-ammoniopropanoate)|beta,beta'-Dithiodialanine|L-Cysteine disulfide|E921
What are the physical properties of L-cystine?
Melting Point 260.5 °C (decomp)
Boiling Point 468.2±45.0 °C(Predicted)
Density 7.8 g/cm³
Appearance White crystalline powder
Color White
Form Powder/Solid
Water Solubility 0.112 g/L (25 ºC)
Refractive Index -222.5 ° (C=1, 1mol/L HCl)
pH 4.60
Log P 0.773 (est)
Which trade and regulatory codes apply to L-cystine?
HS Code 29309014
Storage Class 11 - Combustible Solids
WGK (Germany) 3