XPS and FTIR studies of fungus-stained Daemonorops margaritae

Abstract

We explored the discoloration of rattan cane using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). XPS analysis showed that after the cane was stained by Lasiodiplodia theobromae, carbon and oxygen elements and the ratio of oxygen to carbon decreased. Considering atomic binding, C₁ and C₄ contents increased, while C₂ and C₃ contents decreased, and the ratio of O₂ to O₁ decreased sharply. The relative contents of lignin, cellulose and polysaccharides increased and new substances with low O₂/O₁ ratio occurred. FTIR analysis showed that the absorption peaks of O–H at 3346 cm⁻¹, aliphatic C–H at 2921, 2853 and 1464 cm⁻¹, and C=O at 1723 cm⁻¹, were characteristic peaks of fungal melanin intensified, indicating that cane discoloration was primarily caused by fungal melanin. The absorption peaks characterizing cellulose and lignin like polysaccharides at 800 cm⁻¹, C–H at 1374 cm⁻¹, C–O at 1058 and 1038 cm⁻¹, phenolic hydroxyl at 1245 cm⁻¹, aromatic ether bonds at 1270 cm⁻¹, carbon skeleton at 1608 cm⁻¹ and benzene ring at 1500 cm⁻¹ were enhanced since the fungus mainly consumed the extractives in cane cell lumens and the main composition content increased relatively. Regardless of the discoloration caused by natural fungi or inoculated fungi, the discoloring feature and composition changes were identical except that the fungus-inoculated cane had more melanin.