半纤维素原料的预处理及酶解制备低聚木糖的研究
文献类型：学位论文
| 作者 | 张跃冬 |
| 学位类别 | 博士 |
| 答辩日期 | 2015-06 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 彭辉，王海松 |
| 关键词 | 低聚木糖 木质生物质 预处理 半纤维素 玉米芯 |
| 学位专业 | 化学工程 |
| 中文摘要 | 低聚木糖是一种在食品及饲料行业中广泛应用的高附加值功能性多糖产品，主要由农林半纤维素原料通过半纤维素水解制得，但现行酸水解工艺对设备腐蚀性强、环境污染严重，所以绿色环保的酶水解得到了快速发展，但仍存在着预处理能耗高、水解效率低等问题亟待解决。针对上述瓶颈问题，本文探讨了温和预处理提高玉米芯半纤维素酶解效率的方法，考察了预处理前后半纤维素底物成分结构与其酶解效果的量化关系；研究了以化纤厂碱溶半纤维素废液为原料，经预处理分离纯化酶解制备低聚木糖的新工艺，扩大了低聚木糖的来源范围。 |
| 英文摘要 | Xylooligosaccharides (XOS) are functional oligosaccharide with high additional value which are widely used in food and feed industry. Nowadays, XOS are mainly produced by the acid hydrolysis of xylan-rich hemicelluloses. However, the enzymatic process still suffers from several problems such as the high energy consumption, usage of corrosion reagent in the pretreatment. To solve these problems, the present work focused on mild pretreatments to improve the hydrolysis of xylan in corn cob . We discuss the qualitative relationships between the structure of biomass and its enzymatic hydrolysis effect. On this basis, a process for the production of XOS from pulping waste hemicellulose was established. (1)A two-stage enzymatic hydrolysis was used to evaluate the mild pretreatment. In Stage 1, the pretreated corn cob was first hydrolyzed by xylanase to produce XOS. In Stage 2, the solid residue isolated from Stage 1 was further hydrolyzed by cellulase and β-glucosidase. Alkali deacetylation and autohydrolysis were applied to improve the two-stage enzymatic hydrolysis. The type (NaOH, Na2CO3, Ca(OH)2) and charge of alkali in the deacetylation, the temperature, solid loading and holding time of autohydrolysis were optimized. XRD, FT-IR, SEM and Simen’s staining were applied to understand the mechanism of the hydrolysis promoted by deacetylation and autohydrolysis. The result shows that alkali deacetylation causes the hemicellulose swelling by removing the acetyl group on the xylan backbone, thus enlarge the accessibility of the substrate, which makes the hemicellulose more fragile to the enzymatic attack. The XOS produced from corn cob pretreated by autohydrolysis was mainly coming from the soluble xylan separated by the acetic acid. The acetic acid was produced by deacetylation of the xylan under the thermal hydrolysis. (2)The qualitative relationship between the structure of biomass and the effect of its enzymatic hydrolysis was further studied. Alkali deacetylated corn cobs were used as hydrolysis substrates. Using Spearman correlation coefficients as criterion, there was a low correlation between the content of lignin and the effect of enzymatic hydrolysis, as well as the crystallinity index of the corn cob. Meanwhile, the enzyme accessibility characterized by simen’s staining, as well as the ratio between the content of acetyl group and xylan (A/X) were observed to have strong correlation with the effect of enzymatic hydrolysis. The relationship between A/X and the percentage of xylan hydrolysis could be fitted by an exponential decay function with R2=0.9316. The result shows that for the biomass mildly pretreated by the alkali deacetylation, the acetyl group on the xylan backbone was the most important factor to influence the accessibility of enzyme and the effect of enzymatic hydrolysis. (3)The refining process was applied to the mild pretreatment to further improve the enzymatic hydrolysis. The structures of the deacetylated corn cob before and after PFI mill refining were characterized. The result shows that refining could improve the enzyme hydrolysis by not only enlarging the accessibility of the biomass surface, but also swelling and relaxing the inside of biomass. For the mild pretreatment like alkali deacetylation and autohydrolysis, the improvement of enzymatic hydrolysis after refining were more significant than the common pretreatment. With the addition of PFI refining, the XOS yield after the two-stage enzymatic hydrolysis from the corn cob pretreated by alkali deacetylation and autohydrolysis were 0.188 and 0.175 g/g corn cob, respectively, while the total sugar yields were 0.661 and 0.425 g/g corn cob, respectively. On the basis of the experimental result, the alkali deacetylation and refining pretreatment process was continuously scaled-up using a twin-screw extrusion equipment, the autohydrolysis and refining process was scaled-up using a laboratory pulping digester and a high-solid-loading discmill. The usage of the commercial pulping equipment in the realization of the mild pretreatments showed a great opportunity in industrial application. (4)The structure of the hemicellulose in the pulping waste was characterized and the hemicellulose was used to produce XOS. It was confirmed that the hemicelluloses were (1-4)-linked-D-xylans with few 4-O-methyl-D-glucuronic acid and arabinofuranosyl residues attached. After purified by the acid precipitation and washing, the hemicellulose was pretreated by dilute acid of pH 4.5 in 160ºC for 30min, then subjected to xylase hydrolysis. The XOS yield was 0.541g/g xylan. After spray-dry, the XOS product could meet the feeding standard. |
| 学科主题 | 工科 |
| 语种 | 中文 |
| 公开日期 | 2016 |
| 源URL | [http://ir.qibebt.ac.cn/handle/337004/8085]  |
| 专题 | 青岛生物能源与过程研究所_绿色化学催化团队 |
| 作者单位 | 中国科学院青岛生物能源与过程研究所 |
| 推荐引用方式 GB/T 7714 | 张跃冬. 半纤维素原料的预处理及酶解制备低聚木糖的研究[D]. 北京. 中国科学院研究生院. 2015. |
入库方式： OAI收割
来源：青岛生物能源与过程研究所
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