Saccharification Xylan

The two most important natural pentoses, 1 -arabinose and 1 -xylose, occur in nature as polymeric anhydrides, the so-called pentosans, viz. araban, the chief constituent of many vegetable gums (cherry gum, gum arabic, bran gum), and xylan, in wood. From these pentapolyoses there are produced by hydrolysis first the simple pentoses which are then converted by sufficiently strong acids into furfural. This aldehyde is thus also produced as a by-product in the saccharification of wood (cellulose) by dilute acids. Furfural, being a tertiary aldehyde, is very similar to benzaldehyde, and like the latter undergoes the acyloin reaction (furoin) and takes part in the Perkin synthesis. It also resembles benzaldehyde in its reaction with ammonia (p. 215). 

Bergius-Willstatter saccharification process. Process for industrial production of fermentable sugar from wood by hydrolysis of tannin and xylan-free cellulose with 40-45% hydrochloric acid. The use of concentrated acid requires acid-resistant equipment and recovery of acid. The sugar produced must be rehydrolyzed prior to fermentation. 

Enzyme activity loss because of non-productive adsorption on lignin surface was identified as one of the important factors to decrease enzyme effectiveness, and the effect of surfactants and non-catalytic protein on the enzymatic hydrolysis has been extensively studied to increase the enzymatic hydrolysis of cellulose into fermentable sugars [7, 9 19]. The reported study showed that the non-ionic surfactant poly(oxyethylene)2o-sorbitan-monooleate (Tween 80) enhanced the enzymatic hydrolysis rate and extent of newspaper cellulose by 33 and 14%, respectively [20]. It was also found that 30% more FPU cellulase activity remained in solution, and about three times more recoverable FPU activity could be recycled with the presence of Tween 80. Tween 80 enhanced enzymatic hydrolysis yields for steam-exploded poplar wood by 20% in the simultaneous saccharification and fermentation (SSF) process [21]. Helle et al. [22] reported that hydrolysis yield increased by as much as a factor of 7, whereas enzyme adsorption on cellulose decreased because of the addition of Tween 80. With the presence of poly(oxyethylene)2o-sorbitan-monolaurate (Tween 20) and Tween 80, the conversions of cellulose and xylan in lime-pretreated com stover were increased by 42 and 40%, respectively [23]. Wu and Ju [24] showed that the addition of Tween 20 or Tween 80 to waste newsprint could increase cellulose conversion by about 50% with the saving of cellulase loading of 80%. With the addition of non-ionic, anionic, and cationic surfactants to the hydrolysis of cellulose (Avicel, tissue paper, and reclaimed paper), Ooshima et al. [25] subsequently found that Tween 20 was the most effective for the enhancement of cellulose conversion, and anionic surfactants did not have any effect on cellulose hydrolysis. With the addition of Tween 20 in the SSF process for... 

C, [ago -75°- -19 (H O) p-DL-xylo-pyranose, OL-form, mp. 129 -131 °C. The L-forms are not natural. An aqueous solution of X. at, e.g., 31 °C, contains 36.5% a-pyranose, 63% )S-pyranose, <1% a-and /3-furanose, and 0.02% aldehyde. X. is obtained technically from the saccharification of wood and from the residues of cellulose production or, respectively, by isolation from xylans or from ears of corn by hydrolysis with dilute acids. Reduction of X. furnishes xylitol which can be used as a sugar substitute. X. itself would also be suitable for use as a sweetener but has only half the sweetness of saccharose and also shows laxative effects. 

Most biotechnological applications of hemicellulose utilize acid and/or solvent-based hydrolysates, in which the native xylan is cleaved to xylose and xylose oligomers. This saccharification can be achieved through such chemical means, but also by physical and/or enzymatic methods. Forest biomass is often treated with dilute acid or enzymatic hydrolysis as a pretreatment for fermentative application of the hemicellulosic fraction. Dilute acid hydrolysis generally uses low concentrations of mineral acids (H2SO4, HCl, 2-5%) at high temperatures (e.g. 150-170 °C) and pressures (10 atm) (Sun and Cheng, 2002). Concentrated... 

---