Aging in Keratin Fibers Involving Thiol Groups and Disulphide Crosslinks

Abstract

At any given time the stress-relaxation and water-swollen properties of keratin fibers are different from root to tip: beginning at the root-end, the stress-relaxation decreases, while the water-swollen diameter increases, as one samples toward the tip. This pattern changes with time, the root-end becoming more tip-like until in old fibers (greater than about five years) the properties are uniform along the fiber. This aging process correlates with a gradual decrease in the thiol content of samples taken progressively toward the tip-end. Atmospheric oxidation of thiol groups and also of disulphide would account for the process, although the results strongly suggest that an equilibrium is reached—i.e ., not all the thiol is oxidized, and only about 20% of the disulphide is oxidized to cysteic acid.

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