以蒸爆技術自狼尾草萃取半纖維素的研究

Extraction of Hemicellulose from Napiergrass via Steam　Explosion

鍾仁醫(Jen-Yi Chung)

指導教授 ： 余琬琴

國立臺北科技大學/工程學院/有機高分子研究所/碩士(2011年)

https://doi.org/10.6841/NTUT.2011.00146

摘要

狼尾草是深具潛力的能源作物，此外在台灣狼尾草汁也被開發為健康食品，但其榨汁後的殘渣尚未有合適的利用。為了有效利用狼尾草，我們以蒸爆技術處理狼尾草渣，開發同時生產木寡糖與高消化率芻料的製程。
本實驗室先前以酸性蒸爆條件處理狼尾草，可使半纖維素降解成寡糖溶於蒸爆液中。但是蒸爆液中也含有單糖及各類雜質，包括有機酸(如醋酸)、醣類衍生物(如糠醛furfural, 甲基糠醛hydroxymethylfurfural, 簡稱HMF)等成分。因此要得到高純度的食品級木寡糖，必須去除上述雜質，尤其是具致癌性的糠醛和甲基糠醛。但是木寡糖與糠醛和甲基糠醛的分離相當困難，因此本論文改採用鹼性蒸爆製程，先以蒸爆法萃取木聚醣，再配合後續的酵素水解程序生產木寡糖。鹼性環境會抑制糠醛與羥甲基糠醛這類有害物質的生成，而且萃取的半纖維素將大多以聚醣的形式存在。
本論文的研究重點在鹼性蒸爆萃取條件的最適化，利用實驗設計法，探討蒸爆反應時間、溫度、鹼液濃度對半纖維素的萃取與固體殘渣消化率的影響。反應時間、溫度與Na2CO3濃度的範圍分別為5~25 min、180~210℃與0~2 wt％。固體殘渣的消化率則以酵素法(pepsin-cellulase method)測定。研究結果顯示，鹼的添加大幅減少單糖、HMF與furfural的生成，也使蒸爆液不含木二糖至木四糖，但是卻促進了醋酸的生成。蒸爆溫度與Na2CO3濃度對半纖維素的萃取以及木質素的移除有較顯著的影響，而蒸爆時間的影響則較不顯著。有幾個蒸爆條件可獲得相當高的木聚醣萃取率，均達38-39％，但是若要同時兼顧醣類回收率、固體殘渣消化率、操作時間等因素，較適合的鹼性蒸爆條件為190℃、15 min、2 wt% Na2CO3，此條件的固體殘渣消化率為62.5%。

關鍵字

狼尾草 ； 蒸爆法 ； 木寡糖 ； 消化率 ； 實驗設計

並列摘要

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%.

並列關鍵字

lignocelllosic material ； steam explosion ； digestibility ； animal feed ； Xylo-oligosaccharides ； pepsin-cellulase method ； experimental design

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