Variation in anatomical characteristics and chemical compositions during the sapwood to heartwood transformation of cultivated teak and their relationships to color formation

The interplay between the anatomical structure, chemical compositions, and color of teak wood is not yet fully understood. An analysis of the anatomical structure and chemical compositions from sapwood to heartwood of cultivated teak (Tectona grandis L.f.) was conducted to elucidate the radial variation in wood color. Extractives were generated within the ray parenchyma cells located in the transition (T) zone, and subsequently infiltrated vessel lumina through the pits in the heartwood, accompanied by the disintegration of the nucleus and the disappearance of starch grains. As heartwood developed, the conjugated carbonyl groups in lignin increased, while the S/G ratio experienced a marked rise within the inner heartwood. The extractive content reached a maximum value in the outer heartwood. Signal intensities for squalene and 2-methyl-9,10-anthracenedione in heartwood were approximately 2.8 and 1.4 times greater than those found in sapwood, respectively. Lapachol only appeared in heartwood. A decrease in the L^* value of heartwood was noted in contrast to sapwood, and the color shifted towards red and yellow from sapwood to heartwood. The color difference quantified between sapwood and heartwood was 12.90. The anatomical structure provides the formation and storage spaces, and transportation channels for the extractives. The changes in lignin structure and extractive components are directly linked to the development of wood coloration. Overall, the study contributes to a deep understanding of the relationships between the microstructure, chemical compositions and color formation of teak wood, and will provide insights for the high-value utilization of cultivated precious wood.