Cellulase lignins

Steam-Explosion, Acidolysis, Organosolv, and Cellulase Lignins. 

Acidolysis lignins, organosolv, and cellulase lignins are presently laboratory curiosities due to a lack of commercialization. Whether these lignins will offer any advantages at all with respect to resin adhesives currently used remains to be established. Preliminary experiments [e.g., with acidolysis lignins (81)] have not demonstrated any superior qualities to date. 

Pretreatment of Substrate. Several different lignocelluloses were pretreated with NaOH. This pretreatment partially solubilizes the hemicelluloses and lignin and swells the cellulose so that the organism can utilize it for its growth and for production of a cellulase system in SSF. The treated lignocelluloses were not washed. The NaOH treatment is done with a minimum amount of water so that, after the addition of nutrient solution and inoculum, the moisture content is less than 80% wt/wt and there is no free water in the medium. More water was added to make suspensions of different lignocellulosic substrates of the desired concentration (1% or 5%) for liquid-state (submerged) fermentation (LSF). 

Extraction of the cellulase system. The culture of SSF from each flask (originally 5 g of substrate) was mixed well with more water to bring the final weight of the mixture (mycelium plus unutilized lignin, cellulose, and hemicelluloses) to 100 g. Tween 80 was added at a rate of 0.1%. The mixture was shaken for 0.5 h and centrifuged. The supernatant was used for enzyme determination. We estimated that about 7% to 10% cellulases remained adsorbed on the residues (mycelium and unutilized cellulose, hemicelluloses, and lignin) when the residues were suspended in water and Tween 80 as before and the supernatant was tested for cellulase titer. 

Three laccase preparations (I, II and III) were isolated from the racellular culture medium of Coriolus versicolor by consecutive fractionation through Sephadex G50 and DEAE Sephadex A25 (84). The laccase III preparation at pH 4.0 reduced the apparent molecular weight of a lignin-derived fraction that had been obtained by eluting the water-soluble extract of a cellulase treated ezomatsu wood residue through... 

When autohydrolysed aspen was treated with cellulase enzyme, poor results were obtained. Based on a ton of dry wood, only about 300 lb of fermentable sugars were obtained, and the fermentation was very inefficient with low yields of ethanol. These results compare poorly with those shown in Figure 5 when autohy-drolysed-caustic extracted aspen was treated with cellulase enzyme, and then fermented. It would appear from these results that the caustic extraction step for lignin removal would be necessary if the enzymatic hydrolysis process were to be adopted and advisable when acid hydrolysis is used. 

The same facts apply to biodegradative processes Five years ago, little was known about the enzymology of lignin biodegradation, and the molecular biology of cellulases was in its infancy. Advances have since been made in leaps and bounds these advances are fully discussed within this volume. 

The following experiments were conducted using fraction C-l-A, which was thought to be representative of the LCC s (17). The acidic LCC fraction, C-l-A, was partially hydrolyzed with a cellulase preparation, Cellu-losin AC, and changes in the lignin and sugar distributions were analyzed... 

Lignin was also supposed to cause steric hindrance to cellulases during softwood hydrolysis (Ramos et al., 1992 Mooney et al., 1998, 1999) due to encapsulation of the cellulose component so that the cellulose is less accessible to the biocatalyst (Fan et al., 1980). 

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