The unmasking of lignin structures in wheat straw by alkali

• Published in: Phytochemistry (Oxford) Vol. 63; no. 5; pp. 617 - 623
• Main Authors: Durot, Nathalie, Gaudard, François, Kurek, Bernard
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 01-07-2003; Elsevier
• Subjects: Abiotic reaction; Alkaline extraction; Biological and medical sciences; Carbonates; Cell Wall - chemistry; Chemical constitution; Fractionation; Fundamental and applied biological sciences. Psychology; Lignin; Lignin - chemistry; Lignin - isolation & purification; Lignin carbohydrate complexes; Plant physiology and development; Plant Stems - chemistry; Potassium; Sodium Hydroxide; Triticum - chemistry; Uronic acids; Wheat straw; Lignin; Alkaline extraction; Fractionation; Lignin carbohydrate complexes; Uronic acids; Wheat straw; Abiotic reaction; Complexation; Monocotyledones; Lignin: Lignin carbohydrate complexes; Molecular structure; Cereal crop; Straw; Fractionation: Abiotic reaction; Gramineae; Angiospermae; Biopolymer; Uronic acid; Spermatophyta; Carbohydrate; Triticum aestivum
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/S0031-9422(03)00187-0

This study reports on the structural modifications of wheat straw cell wall promoted by potassium carbonate and sodium hydroxide that lead to the unmasking of some lignin structures. The first impact of the treatments was the extraction of a particular fraction of lignin enriched in C–C linked structures compared to the mean composition in reference wheat straw. Concomitantly, an apparent increase in the amount of lignin monomers released by the cleavage of alkyl–aryl ether bonds was observed in alkali-extracted samples. By summing the amount of ether linked monomers analyzed by thioacidolysis in the solubilized lignin to that found in the extracted wheat straw, an excess of up to 37% is apparent, relative to the corresponding amount in the reference wheat straw. Other modifications of the cell wall were also found. Indeed, a fraction of uronic acids was lost during the treatments and a new fractionation pattern of the lignin-carbohydrate complexes was evidenced. It can thus be concluded that a significant proportion of lignin within the cell wall was unmasked after (i) the selective removal of a particular lignin fraction, (ii) a partial saponification of the esterified fraction of lignin with uronic acids and (iii) a modification of the interactions between the cell wall constituents.
The unmasking of particular lignin structures after a mild alkali treatment of wheat straw, that are otherwise not available for thioacidolysis analysis, is reported.