Application of Pyrolysis-Gas Chromatography-Mass Spectrometry in Studying Microbial Degradation Mechanism of Lignocellulose in Palm Leaf Manuscripts

Palm leaves are traditional writing materials with great cultural value in Southeast Asia. Their primary components, lignocelluloses, are highly susceptible to mold degradation, leading to material embrittlement, information loss, and a serious threat to the preservation of these cultural relics. To investigate the degradation mechanism of palm leaf manuscripts by molds, pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) was employed to systematically analyze the samples inoculated with Penicillium sp., Aspergillus carneus, and Alternaria sp. isolated from palm leaf manuscripts, after 5 weeks of simulated degradation at 28 ℃ and relative humidity of 80%. Qualitative and semi-quantitative analysis of characteristic pyrolysis products revealed the degradation pathways and differences among lignocellulose components. The results indicated that holocellulose was the preferentially degraded component, as evidenced by a decrease in the relative content of its marker products, such as levoglucosan and furfural, leading to a reduction in the holocellulose-to-lignin (H/L) ratio from an initial 0.64 to a range of 0.56–0.24 at the fifth week. Simultaneously, lignin underwent depolymerization, with the relative content of phenol in its pyrolysis products increasing significantly from 0.09 to 0.20–0.24 within the first week of degradation, accompanied by an upward trend in short-chain phenols. Lignin degradation exhibited notable monomer selectivity, as syringyl (S) units were more readily degraded in the initial stage compared to guaiacyl (G) units, reflected by a significant decrease in the S/G ratio during the first week, however, the degradation of S and G monomers showed relative fluctuations between the first week and the fifth week. This study systematically clarified the degradation mechanism of palm leaf lignocellulose by three typical mold species and represented the first application of Py-GC/MS to reveal the differential degradation pathways of lignocellulose components in palm leaf manuscripts at the molecular level. This research provided crucial experimental evidence and molecular markers for subsequent studies on the mold degradation mechanisms and targeted conservation strategies for palm leaf manuscripts and other lignocellulose-based cultural relics.