Lignin Klason

Determination of Lignin Content. Lignin content in plants (wood) is determined by direct or indirect methods (21). The direct method includes measurement of acid-insoluble (ie, Klason) lignin after digesting wood with 72% sulfuric acid to solubilize carbohydrates (22). The Klason lignin contents of representative lignifted materials are shown in Table 2. 

Table 2. Klason Lignin Contents of Lignified Materials ...

DF dietary fiber Cel cellulose Rha rhamnose Fuc fucose Ara arabinose Xyl xylose Man mannose Gal galactose Glu glucose U. ac. uronic acids KL Klason lignin n.d. not determined t traces Source Englyst and Cummings 1988 Englyst and others 1988 Marlett and Vollendorf 1994. 

Chemical and Spectroscopic Analyses. Acid insoluble lignin (Klason lignin) contents of wood species before and after extractions were determined using a modified procedure suitable for small samples (35). 

Figure 2 shows the extent of dissolution of red spruce in methylamine, the amount of precipitate collected in the first trap upon complete depressurization to 1 bar, and the Klason lignin content in the wood residue after extraction, as functions of extraction time. The total dissolution and precipitation are normalized with respect to oven dry weight of initial wood. The extraction conditions were 185°C, 275 bar, and 1 g/min solvent flow rate. As shown in the figure, dissolution initially increases with time and levels off at about 28% by weight. The precipitates which were collected as solids follow a similar trend. The Klason lignin content of the wood residue decreases with extraction time, from an initial value of 26.5% down to 10.1% after 5 h of extraction. 

The solvolytic treatment and the recovery procedures employed yielded about 75% of the original Klason lignin present in the wood. This percentage could be further optimized but was not attempted in the present work. The recovered lignin was subjected to alkaline depolymerization. Yields presented throughout the paper are expressed as percentages of the recovered lignin. 

Yasuda and Terashima (11) recently showed that lignin under Klason lignin determination conditions afforded mefa-linked products. Vanillyl alcohol (4) yielded after reflux in 5% sulfuric acid, mefa-linked product (8) (Fig. 3). 

In all reactions, wood of white fir Abies concolor) has been used. For the alkaline nitrobenzene reactions, extractive-free —20+40 mesh heart-wood sawdust containing 28.0% Klason lignin was used. Sequential extraction of the original sawdust with alcohol-benzene, 95% ethanol, and hot water gave extractives amounting to 4.9, 0.5, and 1.2%, respectively. In the other oxidation reactions, nominal 5 -in. wood chips, commonly used in pulping procedures, were employed. The mixed sap wood-heart-wood chips contained 26.5% Klason lignin and sequential extractives of 3.3, 0.5, and 3.2%, respectively. 

Solvent-extracted wood meal (50 grams), dioxane-water (1 1) (400 ml.), Raney nickel (10 grams), initial hydrogen pressure (500 p.s.i.g.), time 5 hours. In each case the total yield of products represented approximately 26% of the original Klason lignin. 

CHCl3-soluble fraction (% 77 15 of Klason lignin) Chromatographable Products (% of Klason lignin) 78 93 37... 

Table III shows the results of such a study. The variation in the nature of the lignin degradation products with initial pH follows the same general pattern as observed using aspen wood—i.e., an increased percentage of the phenylpropane over the phenylpropanol derivative in acid medium and the almost sole production of phenylethane products under alkaline conditions. The total yield of identified products, based on original Klason lignin, is significantly less than that for aspen (Table I).

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