Softwoods hydrolysis

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). 

Carbohydrates. Carbohydrates are the principal components of the cell wall, comprising 65—75% by weight of the dry wood. Total hydrolysis yields simple sugars, primarily glucose and xylose in hardwoods and glucose and mannose in softwoods. Minor amounts of galactose, arabinose, and rhamnose are present. 

Charles, N., Mansfield, S. D., Mirochnik, O., and Duff, S. J.B., 2003, Effect of oxygen delignification operating parameters on downstream enzymatic hydrolysis of softwood substrates, Biotechnol. Progr. 19 1606-1611. 

Isolation and characterization of lignin structures Hydrolysis and separation. Mild hydrolysis has previously been used for the structural analysis of both softwood and hardwood lignins (10 -14). About 20% of the lignin was liberated from spruce wood and 40% of the lignin from beech wood by percolation of finely ground wood meal with water at 100 °C for several weeks (72). Such a mild hydrolytic treatment can be expected to lead to the rupture of only... 

Recent studies have proven ethanol to be an ideal liquid fuel for transportation and renewable lignocellulosic biomass to be an attractive feedstock for ethanol fuel production by fermentation (1,2). The major fermentable sugars from hydrolysis of lignocellulosic biomass, such as rice and wheat straw, sugarcane bagasse, corn stover, corn fiber, softwood, hardwood, and grasses, are D-glucose and D-xylose except that softwood... 

A typical wood-to-ethanol bioconversion process consists of at least three major steps pretreatment, hydrolysis, and fermentation. The pretreatment stage has been shown to be the key step to providing a substrate susceptible to the subsequent hydrolysis. Steam explosion is one of the most intensively studied pretreatment methods for bioconversion of softwood materials (6-10). 

Effects of Sugar Inhibition on Cellulases and (3-Glucosidase During Enzymatic Hydrolysis of Softwood Substrates... 

In the present study, we quantified the degree of inhibition on both P-glucosidase and cellulase mixtures by glucose and cellobiose at different concentrations. We also determined the inhibitory effects of mannose, galactose, and xylose on both P-glucosidase and cellulase activities and assessed the potential to increase the final sugar concentration by supplementing cellulosic substrate hydrolysis with hemicellulose-rich stream-obtained from steam exploded softwood (prehydrolysate). 

A 72-h hydrolysis profile of a 10% acetic acid-pretreated softwood substrate (Fig. 1) represents a typical enzymatic cellulose hydrolysis course with the majority of the cellulose (up to 70%) broken down within the first 24 h. However, the conversion of the remaining cellulose ( 30%) was incomplete, even after another 2 d of incubation. The decrease in the hydrolysis rate in the latter phase is likely owing to accumulation of end products. To demonstrate that the end products played a major inhibitory role, we removed the produced sugar from the hydrolysate through ultrafiltration. Fresh buffer was then added to the retained protein and the residual substrate to attain the initial volume, and the hydrolysis was continued under the same condition. As shown in Fig. 1, significant increases in the hydrolysis rate were observed after the sugar removal at both 24 h and 48 h of incubation, with complete hydrolysis attained after 48 h and 60 h of incubation respectively. 

Fig. 7. Inhibitory effects of supplemented hemicellulose-derived sugars on hydrolysis of 10% acetic acid-pretreated softwood.

Fig. 9. Total sugar concentrations during combined hydrolysis (10% acetic acid-pretreated softwood substrate with prehydrolysate).

Mooney, C. A., Mansfield, S. D.,Touhy, M. G., and Saddler, J. N. 1998.The effect of initial pore volume and lignin content on the enzymatic hydrolysis of softwoods. Bioresour. Technol., 64,113-119. 

Shevchenko, S. M., Chang, K., Dick, D. G., Gregg, D. J., and Saddler, J. N., Structure and properties of lignin in softwoods after S02-catalyzed steam explosion and enzymatic hydrolysis. Cellulose Chem Technol 2001, 35 (5-6), 487-502. 

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