Integrated analysis of cork presence in Korean oak barks using visual inspection, colorimetry, FT-IR, and Py-GC/MS

Six oak species are native to Korea, but a visible cork layer is present only in Quercus variabilis. The potential of the other Korean oak species for cork applications remains unexplored. This study used colorimetry, FT-IR, and Py-GC/MS to compare the cork composition of Quercus acutissima, Q. aliena, Q. dentata, Q. mongolica, Q. serrata, and Q. variabilis. The analysis focused on suberin and lignin, the main cork components, by identifying their pyrolysis products. Methanolysis with 3% NaOCH₃ revealed approximately 20% suberin content in all species except Q. variabilis, which showed around 40%. Py-GC/MS differentiated suberin-derived fatty acids—found exclusively in cork tissue—from other fatty acids present in the rhytidome. Q. variabilis exhibited 2 to 8 times higher levels of suberin-derived fatty acids and abundant lignin monomers, mainly guaiacyl (G) units. In contrast, lignin monomers were undetectable in Q. acutissima, Q. aliena, and Q. dentata, suggesting either very low levels or concentrations below the instrument’s detection limit. Syringyl (S) monomers were also absent in Q. mongolica and Q. serrata. These findings suggest that lignin composition, along with visual cork layer assessment, can help evaluate the cork potential of Korean oak species and identify viable substitutes for commercial cork.