L-cystine

White hexagonal plate crystal or white crystalline powder, soluble in dilute acid and alkali solution, very difficult to dissolve in water, insoluble in ethanol. There is a small amount of protein, which is mainly contained in keratin of hair, fingers and claws.

In medicine, it is used as raw material for producing antidote and expectorant; in food industry, it is used as dairy additive and bread accelerator. After heating with sugar in food, it can produce all kinds of special fragrance and prevent oil oxidation. It is widely used in food processing; in cosmetics industry, it is used as raw material for producing perm essence.