4.4. Determination of the Lignin Content by the Klason Method

The Klason lignin content was estimated as the residue after sulfuric acid hydrolysis of 300 mg of pre-extracted material (after sequential Soxhlet extraction with acetone, 12 h, methanol, 24 h, and hot water, 12 h), according to TAPPI T222 om-88 [17] and corrected for ash and protein content as previously published [23]. The acid-soluble lignin was determined, after the insoluble lignin was filtered off, by UV-spectroscopy at 205 nm according to [17], using 110 L cm⁻¹ g⁻¹ as the extinction coefficient. Three replicates were measured for each determination. The values displayed in Figure 3 express the sum of Klason-lignin and acid-soluble lignin.