Release of D-Xylose from Wheat Straw by Acid and Xylanase Hydrolysis and Purification of Xylitol

Abstract

Xylitol is a valuable sweetener produced from xylose-rich biomass. Our objective was to optimize conditions for maximum release of D-xylose from wheat straw by acid or enzyme hydrolysis with minimal release of other monosaccharides, and to purify xylitol from three other alditols. Ground straw was treated with 10 parts of 0.2-0.4 M sulfuric acid at 110-130 degrees C for 15-45 min or at reflux with 0.75-1.25 M sulfuric acid for 1.5-3 h. Under optimum conditions of either 0.3 M acid at 123 degrees C for 28 min or 1.0 M acid at 100 degrees C for 3 h, 18 or 19% of D-xylose plus approximately 6% other sugars were produced from straw (dry basis). A 16% yield of D-xylose plus 6% other sugars was obtained when hydrothermally (10% straw, 160 degrees C, 1 h) treated straw was incubated with a commercial xylanase. The lack of enzyme specificity for D-xylose release was attributed to the autohydrolysis of polysaccharides during the pretreatment plus slow hydrolysis of cellulose during enzyme digestion. Xylitol with a purity of 95% was obtained in 10% yield from straw after the reduction of an acid-hydrolyzate followed by fractional crystallization. Purification of the mixture of four alditols by open-column chromatography on a strongly basic anion-exchange resin in hydroxide form gave 7% xylitol crystals with a purity of 99%.

Wheat Straw Autohydrolysis: Process Optimization and Products Characterization

“…In the conditions leading to the highest recovery of XOS, these oligosaccharides contained eight arabinose and three acetyl substituents, respectively, per each 100 xylose units which compares to the initial substitution of xylan chain (17 arabinose and 31 acetyl groups per 100 xylose units) indicating that an efficient and selective removal of the substituents. The results obtained are also in agreement with the previous reported by Liavoga et al [32] for wheat straw XOS obtained by autohydrolysis that also contained a similar level of arabinose substitution. The low content of acetyl groups of these oligosaccharides contrasts with the results obtained for other materials also using autohydrolysis [27,33,33].…”

“…Glucan was almost not affected by the hydrolytic treatment and a solid residue with increased glucan content was obtained. These results are in good agreement with the previous obtained for wheat straw [32] and for other similar feedstocks, e.g., barley straw and rice husks [16]. In the case of wood, little cellulose degradation used to occur at temperatures below 230°C [30].…”

The Effect of Severity Factor on the Release of Xylose and Phenolics from Rice Husk and Rice Straw

“…Due to its amorphous structure, the hemicellulosic fraction of lignocellulosic materials can be easily hydrolyzed by dilute acid treatment, whereas the cellulosic and lignin fractions remain unaltered. Several researchers have studied the dilute acid hydrolysis of different lignocellulosic wastes, such as corn stover [11,12], eucalyptus residue [13], palm waste [14], rapeseed straw [10,15,16], barley straw [10,17,18], wheat straw [19,20], rice husk [2,21] and rice straw [10,[22][23][24][25][26]. However, there are several disadvantages of the dilute acid hydrolysis of these lignocellulosic wastes, such as the production of inhibitors, including acetic acid, furfural [9,17] and phenolics from lignin degradation products [19] and the corrosion of equipment.…”

The Optimization of Dilute Acid Hydrolysis of Cotton Stalk in Xylose Production

“…When the overall xylose yield and selectivity of this study were compared with the previous studies done with wheat straw [12], rice straw [14], and oil palm empty fruit bunch fiber [9], it was found that xylose yield and selectivity were lower. Generally, in lignocellulosic biomass, xylan exists in xylan-lignin complex and becomes resistant to hydrolysis.…”

“…Although controlled acid hydrolysis of lignocellulosic biomass mainly produces xylose from hemicellulose, other by-products such as glucose, acetic acid, and furfural are produced in low amounts [9]. Hemicellulose hydrolysis of different lignocellulosic materials using dilute acid has been studied by many researchers [9][10][11][12][13][14]. The results showed that the amount of sugar released during hydrolysis is dependent on the type of material and operating conditions of the experiment including temperature reaction time and acid concentration [9].…”