XPS and FTIR studies of fungus-stained Daemonorops margaritae

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, C-1 and C-4 contents increased, while C-2 and C-3 contents decreased, and the ratio of O-2 to O-1 decreased sharply. The relative contents of lignin, cellulose and polysaccharides increased and new substances with low O-2/O-1 ratio occurred. FTIR analysis showed that the absorption peaks of O-H at 3346cm(-1), aliphatic C-H at 2921, 2853 and 1464cm(-1), and C=O at 1723cm(-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 800cm(-1), C-H at 1374cm(-1), C-O at 1058 and 1038cm(-1), phenolic hydroxyl at 1245cm(-1), aromatic ether bonds at 1270cm(-1), carbon skeleton at 1608cm(-1) and benzene ring at 1500cm(-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.