Autohydrolysis of Miscanthus X giganteus for the production of xylooligosaccharides

Prebiotics;Pretreatment;XOS;Xylooliosaccharides;Autohydrolysis;Miscanthus x giganteus

Chen, Ming-Hsu

关键词: Prebiotics;    Pretreatment;    XOS;    Xylooliosaccharides;    Autohydrolysis;    Miscanthus x giganteus;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/88687/Chen_Ming-Hsu1.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Miscanthus x giganteus (MxG) is considered a potential bioenergy crop due to its high yield and ecological properties. Xylooligosaccharides (XOS) are sugar oligomers made of xylose units. Due to their prebiotic functionality and other health promoting effects, XOS can be a value added coproduct for the cellulosic ethanol industry. There is lack of information on the production of XOS in conjunction with cellulosic ethanol processes, especially with MxG. The objective of this study was to investigate the production, purification, characterization and biological activity of XOS from MxG. To determine the optimal condition for producing XOS from MxG, autohydrolysis was performed in a steel pipe reactor submerged in a fluidized sand bath. The water/solid ratio was set at 9:1. Temperatures and times were tested from 140°C to 220°C and 0 to 60 min. The XOS could be produced efficiently at 160°C, 60 min or 180°C, 20 min or 200°C, 5 min. Conversions of 13.5% (w/w) initial biomass and 69.2% (w/w) initial xylan into XOS were obtained. Compositions of XOS from three reaction conditions were similar. Soluble XOS were recovered using activated carbon adsorption coupled with ethanol/water elution. The highest recovery of 47.9% (w/w) XOS was recovered by using 10% activated carbon (w/v) and eluted sequentially with 5, 30, 50, 70 and 95% ethanol/water solution. Most XOS were eluted at 30 and 50% ethanol/water solution. Further tests were conducted using gel permeation chromatography (GPC) measuring the molecular weight (MW) distribution in each XOS fraction. Higher ethanol solution recovered higher DP oligomers. Recoveries of 91.8% xylobiose, 86.9% xylotriose, 66.3% xylotetraose, 56.2% xylopentaose and 48.9% xylohexaose from ethanol elution were observed. To separate DP2 to DP6 oligomers into individual fractions, crude XOS hydrolyzate was fractionated by centrifugal partition chromatography (CPC) using a butanol:methanol:water (4:1:4) solvent system. CPC fractions were consolidated and five fractions rich in DP2 to DP6 were collected with recoveries of 90.2% DP2, 64.5% DP3, 71.2% DP4, 61.9% DP5 and 68.9% DP6. Purities of DP2 to DP6 fractions were 61.9, 63.2, 44.5, 31.5, and 51.3%, respectively. DP2 and DP3 fractions were analyzed by ESI-MS; pentobiose and pentotriose were verified as the primary components. The ethanol eluted XOS fractions were combined and further purified. With a combination of different ion exchange resins, most of the impurities and colorants were removed. The end product, MxG XOS, had 76.6% xylose oligomers, 1.5% arabinose oligomers, 4.4% glucose oligomers and 6.9% bound acetyl groups. Total substituted oligosaccharides were 89.3% (w/w). The MxG XOS had 1.7% xylose (X1), 8.9% xylobiose (X2), 11.3% xylotriose (X3), 8.8% xylotetraoase (X4), 9.0% xylopentaose (X5) and 5.8% xylohexaose (X6). Purified MxG XOS were cultured with health beneficial bacteria Bifidobacterium adolescentis and Bifidobacterium catenulatum. Both Bifidobacteria were able to utilize MxG XOS as a carbon source for proliferation while B. adolescentis grew faster than B. catenulatum with specific growth rates of 0.69 to 0.33 (h-1). The substrate utilization was 84.1% by B. adolescentis and 76.9% by B. catenulatum. There are substrate preferences of xylobiose, xylotriose and xylotetraose. Purified MxG XOS were cultured with human fecal microbiota to simulate digestion in the colon. A medium pH drop, from 7.1 to 5.0, was indicative of the utilization of MxG XOS. During 12 h of fermentation, 1 g MxG XOS was metabolized into 466 mg acetic acid, 75 mg propionic acid and 84 mg butyric acid. The short chain fatty acid produced from MxG XOS was the highest amount among three tested substrates. The qPCR was adopted to enumerate bacteria populations. With MxG XOS used as the substrate, the Bifidobacteria spp. and Lactobacillus spp. increased, in addition, there was no significant growth in Clostridium perfringens . We explored the feasibility of producing XOS from MxG in combination with pretreatment, direct purification of XOS from crude hydrolyzate, separation mono DP out of complex XOS oligomers and the biological activities of MxG XOS. The xylose oligomers have application potential to be a coproduct for a cellulosic ethanol plant. The procedure developed in this research can apply to other bioenergy crops with modifications depending upon material property.