自狼尾草蒸爆液純化木寡糖之研究

Purification of xylooligosachharides from steam-explosion liquor of Napiergrass

楊貴茵(Guei-Yin Yang)

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.2011.00580

摘要

狼尾草(pennisetum purpureum)為新興的能源作物，具有生長快速、高產量、耐病蟲害等優點，其汁液因富含維生素、葉酸和抗氧化劑等營養素，已被廣泛應用於機能性食品。而狼尾草渣經預處理與水解糖化後可產製醱酵用的糖液。本研究採用的預處理法為蒸煮爆碎法(steam explosion)，在適當的蒸爆條件下，不但可有效提升狼尾草渣的糖化率，還可得到富含木寡糖的蒸爆液，因此除了從纖維素水解獲得的葡萄糖外，尚可從蒸爆液純化木寡糖。木寡糖是目前當紅的機能性食品，其單體為木糖，聚合度為2~7，不但可做為腸內益生菌(probiotics)的益生素(prebiotics)，達到改善腸相與預防或改善疾病的效果，也可做為糖尿病患者或體重控制者的天然甜味劑。但是蒸爆液內除了木寡糖，還有許多雜質。為了提高木寡糖漿的純度，本論文探討以活性碳吸附、減壓濃縮、醇類沉澱與分子篩液相層析法，去除蒸爆液中有機酸、羥甲基糠醛（hydroxylmethylfurfural, HMF)、糠醛（furfural）及色素等雜質的可能性。
研究結果顯示，活性碳可有效脫色，而減壓濃縮可去除部分的醋酸、羥甲基糠醛與糠醛，將此二步驟串連，脫色效果不顯著，醋酸、羥甲基糠醛與糠醛的去除率分別可達30.8%、35.2%及93.6%，而木寡糖的損失率約為20%。為了去除上述濃縮液中殘留的羥甲基糠醛與糠醛，繼續嘗試以醇類溶劑沉澱或分子篩液相層析法處理濃縮液。結果顯示甲醇、乙醇、異丙醇及丁醇四醇類皆無法有效分離羥甲基糠醛與糠醛；分子篩液相層析法雖有部分分離效果但仍不理想，理論上糠醛與羥甲基糠醛的分子量較木二糖小，所以此二糠醛類雜質的沖提時間應該在木二糖之後，但是其沖提時間卻與木三糖、木四糖的沖提時間重疊，導致本研究僅得到不含糠醛類雜質的木二糖與木五糖。若要完全去除糠醛類雜質，應嘗試其他方法，例如離子交換液相層析法等。

關鍵字

機能性食品 ； 益菌生 ； 木寡糖 ； 狼尾草 ； 蒸煮爆碎法

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. To increase the value of napiergrass, the fibrous residues of napiergrass were subjected to an oxidative steam explosion treatment to generate liquors rich in xylooligosacchrides (XOs). XOs are sugar oligomers made up of xylose units with degree of polymerization of 2 to 7. They show a remarkable potential for utilization in food-related applications because of its benefits for health maintenance and disease prevention. XOs have been shown to reduce cholesterol, improve the biological availability of calcium and maintain gastrointestinal health. However, the steam explosion liquor had a dark color and contained various impurities, including small organic acid, furfural, hydroxylmethylfurfural (HMF) and degraded lignins. In order to obtain food-grade XOs further purification was necessary.
In this study, the following purification methods were investigated: activated carbon adsorption, vacuum evaporation, solvent precipitation, and gel filtration column chromatography. The results show that activated carbon was effective for decolorization, and vacuum evaporation was able to remove part of acetic acid, HMF and furfural in the steam explosion liquor. Combining the activated carbon (1 g/100 ml liquor) and vacuum evaporation treatments, 30.8% of acetic acid, 35.2% of HMF and 93.6% of furfural were removed, with an 80% recovery rate for xylooligosaccharides. To eliminate residual acetic acid, HMF, and furfural in the decolored and concentrated liquor, solvent precipitation and gel filtration column chromatography were tested. The results show that solvent precipitation using methanol, ethanol, isopropanol or butanol could not effectively separate impurities from xylooligosaccharides. The technique of gel filtration chromatography, on the other hand, was able to generate xylobiose and xylopentaose free of HMF and furfural. Unfortunately, both xylotriose and xyloteraose coeluted with HMF and furfural, despite the fact that HMF and furfural have smaller molecular weights and should emerge from the column later than xylobiose. To completely eliminate HMF and furfural from steam explosion liquors, other techniques such as ion exchange chromatography should be tested.

並列關鍵字

functional foods ； probiotics ； xylooligosaccharides ； lignocellulosic materials ； napiergrass ； steam explosion

參考文獻

[21] 蕭淞云，自稻桿與蔗渣生產木寡醣之研究，碩士論文，國立台灣大學食品營養學系，臺中，2006。

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