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 both fermentation and protein hydrolysis.

In commercial applications, it functions as an antioxidant, dough conditioner, and structural protein precursor across food, pharmaceutical, and cosmetic manufacturing sectors worldwide.

In bakery production, it acts as a reducing agent that modifies gluten structure, improving dough extensibility and reducing mixing time in bread and cracker manufacturing processes.

Pharmaceutical formulators use it as an amino acid supplement ingredient in infusion solutions, clinical nutrition products, and tablet formulations targeting metabolic support and recovery.

In personal care, it is incorporated into hair treatment products and keratin-based formulations where its disulfide bonding chemistry supports hair fiber repair and conditioning claims.

Food and beverage manufacturers also use it as an approved processing aid and antioxidant stabilizer under the specific regulatory designation in relevant global markets.

The product is supplied as a white crystalline powder. Standard grades include USP, BP, Ph. Eur., and food-grade (FCC), with pharmaceutical-grade material subject to stricter purity specifications.

Bulk quantities are available from fermentation-derived or hydrolysis-derived sources, with origin documentation increasingly relevant to modern buyer qualification and quality assurance processes.