Extraction of Hemicellulose from Napiergrass via Steam Explosion

• Main Authors: Jen-Yi Chung, 鍾仁醫
• Other Authors: 余琬琴
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/6fncb8

碩士 === 國立臺北科技大學 === 有機高分子研究所 === 99 === Napiergrass (Pennisetum purpureum) is regarded as a potential energy crop and can be used for the production of fuels and chemicals. In addition, napiergrass juice prevails recently in Taiwan as a functional juice due to its beneficial health effects. However, the fibrous residues after juice extraction have not yet found suitable uses. In order to fully utilize the napiergrass biomass, we investigated the clean fractionation of napiergrass using the steam explosion (SE) technology to produce xylo-oligosaccharides and animal feed of high digestibility. Previously, SE was performed without the addition of bases. Under such conditions, SE liquor becomes acidic due to the generation of acetic acid, and part of the hemicellulose is hydrolyzed into oligosaccharides. However, the SE liquor also contains impurities such as monosaccharides, organic acids, furfural and HMF (hydroxymethylfurfural). In order to produce food-grade xylo-oligosaccharides, these impurities, especially the carcinogenic furfural and HMF, need to be removed. However, the separation of xylo-oligosaccharides from furfural and HMF is rather difficult. Consequently, a two-step approach is used here instead, i.e., extraction of xylan and the enzymatic hydrolysis of xylan into xylo-oligosaccharides. To extract xylan, steam explosion should be carried out under basic conditions. The basic conditions should also inhibit the formation of furfural and HMF. This study focuses on the optimization of SE condition for the extraction of xylan and the production of animal feed of high digestibility. The factors investigated included SE temperature, SE time, and the amount of Na2CO3 added during SE. The range of SE temperature, SE time, and the amount of Na2CO3 were180~210℃,5~25 min, and 0~2 wt％, respectively. The digestibility of the residual solids after SE was determined using the pepsin-cellulase method. The results indicate that the addition of Na2CO3 markedly reduced the formation of monosaccharides, furfural and HMF. Furthermore, no xylobiose, xylotriose, or xylotetraose was found in the SE liquor when Na2CO3 was added. The addition of Na2CO3, however, stimulated the formation of acetic acid. Among the SE factors investigated, the SE temperature and Na2CO3% had significant effects on hemicellulose extraction and the digestibility of residual solids. The xylan extraction rate obtained in this study reached 38-39%, and several SE conditions produced similar xylan extraction rates. When other factors including digestibility of residual solids, recovery of carbohydrates, and operation time are considered simultaneously, a suitable SE condition is 190℃, 15 min, and 2 wt% Na2CO3. Under this SE condition, the digestibility of the residual solid was found to be 62.5%.