Determining lignin content

Lignin is a complex phenolic cell wall polymer that is chemically cross-linked with hemicellulose and cell wall proteins. Most of the methods to determine lignin content are based on the removal of all other cell wall constituents, typically through acid hydrolysis, which will readily remove hemicellulose under mild conditions, and non-crystalline cellulose under more severe conditions. Several different methods will be discussed below. The different methods have also been extensively reviewed and compared by Hatfield et al. (1994), Brinkmann et al. (2002), Fukushima and Hatfield (2004), and Hatfield and Fukushima (2005). 

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The acetyl bromide procedure was developed by Johnson et al. (1961) to determine lignin content in small samples from woody species. This method uses acetyl bromide (4.10) to acetylate unbound hydroxyl groups in the lignin (4.11), while the hydroxyl group on the a-carbon is substituted with a bromine group. The substituted lignin derivative (4.12) is soluble under acidic conditions, and its concentration can be measured with a spectrophotometer at 280 nm. 

Chemical analyses to determine lignin content and composition are difficult because of the complex nature of lignin. In addition, they often result in loss of information regarding the original structure. A large number... 

A method based on an IR technique has been patented for determining lignin content (and other pulp properties) of pulp suspensions [109],... 

Y Ni, GJ Kubes, ARP van Heiningen. Methanol number A fast method to determine lignin content of pulp. J Pulp Pap Sci 16(3) J83-J86, 1990. 

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. 

As stated previously, only about 3 % of the lignin content of sound wood was isolated by alcoholic extraction. It was therefore of interest to determine, whether increased amounts of lignin could be extracted from the decayed wood. Thus, both sound and decayed white Scots... 

ABL contents, expressed in ferulic acid equivalents, were of the same order of magnitude as Klason and acid-insoluble lignin contents. However, this agreement was fortuitous as the ABL determination provided only... 

When highly resistant wheat varieties are inoculated with an avirulent race of the stem rust fungus, fungal growth is arrested by the hypersensitive death of the first penetrated host cells (30,31.) Even in very densely inoculated leaves, the reaction of less than one percent of the host cells is sufficient to stop further development of the parasite. This small percentage may be the reason, why no increased content of biochemically determined lignin was measured in infected hypersensitive wheat leaves (60,61). 

However, when an elicitor (see below), isolated from the stem rust fungus (62), is injected into the intercellular spaces of wheat leaves almost every cell in the infiltrated area exhibits a hypersensitive-like reaction (62-65). In the elicitor treated leaves, lignin content as determined by the thioglycolic acid procedure clearly increased (66). 

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). 

Earlier work on chain extended HPLs has shown that these derivatives produce uniform (i.e., single phase) polymers with Tg varying in accordance with the Gordon-Taylor relationship (12). Polyurethanes from chain-extended HPLs were found to be rubber-like at room temperature with modulus declining as lignin content is reduced (8). Star-like structure determines functionality, Tg, viscosity, and several other properties that influence utility as polymer segment. 

Furthermore it must be considered that parts of the lignin are dissolved during the hydrolysis, and therefore the lignin content must be determined indirectly from the difference of polysaccharide and ash content to 100%. Table V shows the data of wood and pulp analysis based on intensive hydrolysis with TFA and calculated under consideration of the mentioned facts. 

It is unclear how accurate this method is for the determination of lignin content in grasses, since a fraction of the lignin from grasses appears to be readily soluble in acidic solutions, such as used in this procedure. This would result in underestimation of the actual lignin content (Hatfield and Fukushima, 2005). 

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