Sepia officinalis melanin

0.4 mg of pigments isolated from C. versicolor cuticle (Figure 3b) was dissolved in 1 mL of 0.1 M KOH, with the assistance of ultrasound treatment, at 80 °C for 30 min. Spectra were obtained for C. versicolor pigment and Sepia officinalis melanin (Sigma). The spectra were measured with a JASCO V-750 spectrometer in the wavelength range of 200 to 800 nm using a quartz cuvette with path length of 1 cm (quartz suprasil, Hellma Analytics, Müllheim, Germany) and operated at a resolution of 5 nm.

UV-VIS spectrum was obtained in the range 190–750 nm using UV–VIS spectrophotometer (Shimadzu UV-2400) 0.1 mol/L NaOH as reference (Suryanarayanan et al. 2004; Selvakumar et al. 2008). A standard melanin spectrum was also obtained using Sepia officinalis melanin (Sigma, Aldrich Chemicals, India). For FTIR spectral analysis, the purified T. albuminosus melanin sample was mixed with KBr (1:10) and pressed into a 1 mm thin pellets. FTIR spectra were recorded between 4000 and 500 cm⁻¹ in transmission/absorbance mode on FTIR spectrometer (Shimadzu IR Prestige 21, Japan) averaging of 40 scans. Spectral resolution was 4 cm⁻¹, encoding interval 1 cm⁻¹, Happ–Genzel apodisation and scanning speed 2.8 mm s⁻¹ (Mbonyiryivuze et al. 2015).

The structure of the pigment isolated from P. putida ESACB 191 was investigated by SEM and compared with the morphology of commercial Sepia officinalis melanin (Sigma, St. Louis, MO, USA). The powder of the two samples was scattered carefully over a double-side carbon tape attached to the aluminum stub surfaces. Then, the material was sputter-coated with gold and the metalized samples observed on a JEOL 5200LV scanning electron microscope (JEOL Ltd., Tokyo, Japan) operating at an accelerating voltage of 20 kV.