Abstract
Optical properties of the biopolymers chitin and chitosan have been considered for wavelengths between 250 and 750nm. First, by inverting published refractive index data for composite chitosan–chitin samples of two independent sources, we have been able to obtain the spectral dependence of both the chitosan and chitin refractive indices. Then light reflection and transmission measurements were carried out for samples obtained from fresh shrimp shells. From these spectrophotometric measurements the chitin refractive index and its extinction coefficient have been obtained for the mentioned spectral range. Absorption of light by chitin is negligible for visible wavelengths. Chitin extinction coefficient displays absorption bands in the near ultraviolet, and it is attributed to the proteinaceous content of chitin. Cuticle proteins have been isolated from these chitin samples, and absorbance measurements support the presence of the aforementioned absorption band. The chitin optical constants are used to model the structural color of a shield bug: the Poecilocoris lewisi.
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