Thioglycolic acid lignin

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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The solid residues analyzed here were produced by supercritical extraction with methanol of Populus tremuloides in a tubular reactor i-S.. The analytical procedures used for these residues were described previously as elemental analysis, Klason lignin test, thioglycolic acid lignin test, recondensed material and carbohydrates, thermogravimebric (TG/DTG) and FTIR il> and ESCA iJ.. Table 1 reports results obtained using these procedures as well as conditions of extraction for each SCE residue. 

Figure 1. Klason residue and thioglycolic acid lignin (TGAL) in SCE solid residues (expressed on dry SCE residue beusis).

As a consequence, we suggest that the difference between the Klason residue and the thioglycolic acid lignin is representative of recondensed material (RM) in SCE residues. The calculated values for recondensed material in these residues are reported in Table 1. Figure 2 gives the values for the percent recondensed material expressed on a dry wood basis. 

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). 

The reaction of thioglycolic acid (4.7) with the benzyl alcohol groups in lignin (4.8) under acidic conditions and at elevated temperatures results in the formation of thioethers that render the derivatized lignin (4.9) soluble in an alkaline solution (Figure 4.2). 

Figure 4-2. Reaction of thioglycolic acid with lignin. Adapted from Hatfield and Fukushima...

Thioglycolic acid can be used for extracting lignin with better yields than alcohols. 

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