自稻桿與蔗渣生產木寡醣之研究

Abstract

木寡醣(xylooligosaccharide)是由2-7個木糖以β-1,4鍵結所形成寡醣，是一種機能性食品。木寡醣能選擇性地增殖腸道中的益菌，改善腸道菌相，這樣的特性稱為益生性(prebiotic)。木寡醣可由纖維性廢棄物以酵素水解法或酸水解法來生產。本篇萃取半纖維素的方法主要分為酒精沈澱與超濃縮過濾收集兩種。半纖維素經由重組的木聚醣酶水解後，利用超濃縮過濾裝置收集小分子部分以純化木寡醣。 以不同鹼濃度配合酒精沈澱法萃取半纖維素，經酵素水解，發現以12% NaOH萃取，可得最佳木寡醣產率。以此方法稻桿與蔗渣的總醣回收率分別為13.3%與12.1%；而半纖維素的水解率則分別為37.8%與39.1%；最終純化木寡醣產物的乾重產率分別為4.8%與4.6%(相對於原料乾重)。 以超濃縮過濾法收集的稻桿與蔗渣半纖維素，其總醣回收率分別為21.0%與17.0%，較酒精沈澱法高；而半纖維素的水解率則分別為15.7%與38.2%；最終純化木寡醣產物的乾重產率分別為4.6%與7.8%(相對於原料乾重)。 水解時的酵素量由20 U/mL提高至200 U/mL可增加還原糖產生的速率與最終水解率。水解產物經HPLC分析是以木三糖為主，木糖含量均僅有約3%(w/w)。 超濃縮過濾法所製的木寡醣產物，經總醣含量與與HPLC分析，結果顯示品質與Suntory 的木寡醣產品XOS 95P。將兩種寡醣進行試管內(in vitro)益生性(Prebiotic)測試，Bifidobacterium bifidum以木寡醣為唯一碳源時經24h培養後的菌數，與利用葡萄糖時相當，而Clostridium perfringens則較低，顯示腸道害菌C. perfringens對木寡醣的利用率較差。

Xylooligosaccharide(XO), which has been considered as a prebiotics, is sugar oligomers made up of 2-7 xylose units by β-1,4 linkage. Xylooligosaccharide can proliferate beneficial bacteria and improve microflora in human gut. Xylooligosaccharides could be produced by using xylanase or acid to hydrolyze hemicellulose in lignocellulosic waste. In this study, two methods were used to extract hemicellulose from rice straw and sugarcane bagasse; one was to precipitate hemicellulose by ethanol after alkaline extraction; the other was to collect hemicellulose by ultrafiltration after alkaline extraction. Hemicellulose was hydrolyzed by a recombinant β-1,4 endo-xylanase. The final xylooligosaccharide product was purified through ultrafiltration. By ethanol precipitation method, NaOH solution with different concentration was used to extract hemicellulose. After hydrolysis, it is found that 12% NaOH was the optimal alkaline concentration yielding the highest amount of reducing sugar. In this way, the hemicellulose yields of rice straw and sugarcane bagasse were 26.0% and 18.5% (w/w) respectively; the hydrolysis percentage were 37.8% and 38.1% respectively; and the xylooligosaccharides yield toward rice straw and sugarcane bagasse were 4.8% and 4.6% (w/w) respectively. By ultrafiltration method, the sugar recovery of rice straw and sugarcane bagasse was 21.0% and 17.9% respectively; the hydrolysis percentage were 37.8% and 38.1% respectively; and the xylooligosaccharides yield toward rice straw and sugarcane bagasse were 4.8% and 4.6% (w/w) ,respectively. Raising enzyme dosage from 20 U/mL to 200 U/mL might increase reducing sugar production and hydrolysis percentage. After HPLC analysis ,the major compound in hydrolysate was xylotriose ,and xylose content was about 3% only. The final xylooligosaccharide products made by ultrafiltration method were analyzed by HPLC and phenol-surfuric acid method, it showed that its quality was similar to xylooligosaccharide products XOS 95P produced from Suntory. Prebiotic effect of xylooligosaccharide products were assayed in vitro. When xylooligosacchaide was added as sole carbon source ,it is found that probiotic strain Bifidobacterium bifidum grew the same way as it did glucose was taken as carbon source, but the harmful strain Clostridium perfringens didnn’t grow that well. Therefore, it showed that xylooligosaccharide was less utilizing by C. perfringens.