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The differences in lignin were studied among three kenaf varieties: Everglades (Hibiscus cannabinus L.), Aokawa-3 (H. cannabinus L.), and Mesta (H. sabdariffa L.). The bast, inner bast, and core samples were each prepared from the four different positions, top, upper middle, lower middle and bottom, of the kenaf stems. With increasing height of the stems, the lignin content decreased. In all kenafs studied, the bast samples contained lignin in lower amounts than the core samples prepared from the same positions. The differences in lignin contents between the core and bast samples were larger in Everglades and Aokawa-3 than in Mesta. The inner bast samples showed similar results to those of the core samples prepared from the same positions. The bast samples produced nitrobenzene oxidation products with larger syringaldehyde/vanillin (S/V) ratios than the core samples prepared from the same positions. Most bast and core from Everglades and Aokawa-3 showed ratios of more than approximately 3.0 and 1.2 S/V, respectively. The average S/V ratios in Mesta were 2.1 for the bast samples and 1.9 for the core samples. These findings showed, the bast samples of the Everglades and Aokawa-3, syringyl lignin units were predominant. Thioacidolysis also provides similar results. These results show that (1) the core lignin is a mixed lignin with guaiacyl and syringyl type, and the bast lignin is syringyl type, from the viewpoint of the lignin composition; and (2) lignin in Everglades and Aokawa-3 is heterogeneous compared to that in Mesta. |
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