| Summary: | 碩士 === 國立宜蘭大學 === 食品科學系碩士班 === 106 === Rice hull is rich in lignocellulose which is composition of cellulose, lignin and hemicellulose. Xylan is the main polysaccharide in hemicellulose and used to enzymatic hydrolysis for producing xylooligosaccharides (XOs). In many study, XOs provides beneficial effects on selective growth stimulation of beneficial gut microflora, anti-oxidant, anti-inflammatory effects and antiallergic activities. In this study, the production of XOs from rice hull by alkaline hydrogen peroxide oxidation and then following enzymatic hydrolysis. As the result, the rice hull is rich in carbohydrates (43.55%), which constituted of 28.54% glucose, 13.2% xylose and 1.81% arabinose. Methods for the one-step extraction of lignin-low xylan from rice hull with alkaline hydrogen peroxide have been developed. The rice hull treatment with 2 N sodium hydroxide and 4% H2O2 at 50°C for 90 minutes under a ratio of 1:20 (solid to liquid ratio) gave a 14.05% yield of xylan. The alkaline extracts of rice hull were neutralized to pH 11 for desilication (83%) then rice xylan was precipitated by alcohol. The xylan of rice hull constituted of 81.4% xylose, 12.4% arabinose and 6.2% glucose. Analyses of the enzymatic hydrolyzate showed the presence of XOs of varying degree of polymerization falling in the range of 2–3. The response surface analysis predicted ideal condition viz., enzyme dose 150 U/g and reaction time 14.71 h for maximizing XOs yield (21.91%), which consist of 33% xylotriose and 67% xylobiose. Therefore, the rice hull was prepared under optimal conditions for the production of 3.07 g XOs per 100 g of rice hull. The results show the suitability of rice hull as a good raw material for extraction of xylan and then enzymatic hydrolysis into XOs.
Keywords: rice hull, xylan, alkaline extraction, xylooligosaccharide, enzymatic hydrolysis.
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