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The Impact of Post-Pretreatment Conditioning on Enzyme Accessibility and Water Interactions in Alkali Pretreated Rice Straw.

机译：预处理条件对碱预处理的稻草中酶的可及性和水相互作用的影响。

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摘要

Rice straw, a high-abundance lignocellulosic residue from rice production has tremendous potential as a feedstock for biofuel production in California. In this study, the impact of post-alkali pretreatment conditioning schemes on enzyme saccharification efficiency was examined, particularly focusing on understanding resulting biomass compositional impacts on water interactions with the biomass and enzyme accessibility to the cellulose fraction. Rice straw was pretreated with sodium hydroxide and subsequently washed by two different conditions: 1) by extensive washing with distilled water to reduce the pH to the optimum for cellulases which is pH 5--6, and 2) immediate pH adjustment to pH 5--6 with hydrochloric acid before extensive washing with distilled water. The two post-pretreatment conditions gave significant differences in ash, acid-insoluble lignin, glucan and xylan compositions. Alkali pretreatment improved cellulase digestibility of rice straw, and water washing improved enzymatic digestibility more than neutralization. Hydrolysis reactions with a purified Trichoderma reesei Cel7A, a reducing-end specific cellulase, demonstrated that the differences in saccharification are likely due to differences in the accessibility of the cellulose fraction to the cellulolytic enzymes.;Further analyses were conducted to study the mobility of the water associated with the rice straw samples by measuring T2 relaxation times of the water protons by 1H-Nuclear Magnetic Resonance (NMR) relaxometry. Results showed significant changes in water association with the rice straw due to the pretreatment and due to the two different post-pretreatment conditions. Pretreatment increased the amount of water at the surface of the rice straw samples as indicated by increased amplitude of the shortest T2 time peaks in the relaxation spectra. Moreover, the amount of water in the first T2 pool in the water washed sample was significantly greater than in the neutralized sample. These results suggest that the specific surface area of rice straw accessible to water protons was increased by the alkali pretreatment, likely due to solubilization of alkali-soluble components of the cell walls. Post-pretreatment processes resulted in differences in the specific surface area likely due to re-precipitation of alkali solubilized components during neutralization. The T2 relaxation times of the surface water pool in washed and raw rice straw were not significantly different, at 4.4 and 4.5 ms, respectively, but both T2 times were significantly shorter than that of the neutralized and then washed sample, at 5.5 ms. The expectation was that the T2 times of the surface water peaks would reflect differences in surface composition of the rice straw samples. Further analysis of surface composition is necessary to further interpret the shortest T2 times observed in the samples.;The T2 spectra of the rice straw samples contained longer T2 time peaks that were interpreted as differences in porosity of the rice straw due to the treatments. Pretreatment caused physical changes to rice straw that impacted water organization (3 peaks to 4 peaks), but the amount of water in the peaks were greater in the washed rice straw than the neutralized rice straw suggesting that water-washed rice straw had more of the larger pores than the neutralized and then washed rice straw. One possible explanation is that the neutralization caused precipitation of alkali solubilized components that filled the volumes of the pores.
机译：稻草是稻米生产中的一种高含量木质纤维素残留物，在加利福尼亚州作为生产生物燃料的原料具有巨大的潜力。在这项研究中，检查了碱预处理预处理方案对酶糖化效率的影响，尤其着重于了解对水与生物质相互作用和酶对纤维素部分的可及性产生的生物质组成影响。稻草用氢氧化钠预处理，然后在两种不同的条件下洗涤：1）用蒸馏水充分洗涤以将pH降低至最适合纤维素酶的pH值，即pH 5--6； 2）立即将pH调节至pH 5- -6用盐酸冲洗，然后用蒸馏水充分洗涤。两种预处理条件在灰分，酸不溶性木质素，葡聚糖和木聚糖的组成上有显着差异。碱预处理可改善稻草的纤维素酶消化率，而水洗比中和处理可改善酶消化率。用纯化的里氏木霉Cel7A（一种还原性末端特异性纤维素酶）进行的水解反应表明，糖化的差异可能是由于纤维素级分对纤维素分解酶的可及性方面的差异所致。通过1H-核磁共振（NMR）弛豫法测量水质子的T2弛豫时间，从而获得与稻草样品相关的水。结果表明，由于预处理以及两种不同的预处理条件，与稻草的水分缔合关系发生了显着变化。预处理增加了稻草样品表面的水量，如弛豫谱中最短T2时间峰的幅度增加所表明。此外，水洗样品中的第一个T2池中的水量明显大于中和样品中的水量。这些结果表明，通过碱预处理可以使质子可接近的稻草比表面积增加，这可能是由于细胞壁的碱溶性成分溶解了。后处理过程可能导致比表面积不同，这可能是由于中和过程中碱溶性组分的再沉淀所致。清洗后的稻草和未加工的稻草中地表水的T2弛豫时间没有显着差异，分别为4.4和4.5 ms，但是两个T2时间均显着小于中和然后清洗的样品的5.5 ms。可以预期，地表水峰的T2倍将反映稻草样品表面成分的差异。需要进一步分析表面成分以进一步解释样品中观察到的最短T2时间。稻草样品的T2光谱包含更长的T2时间峰，这被解释为由于处理导致的稻草孔隙率差异。预处理导致稻草发生物理变化，从而影响了水的组织（3个峰到4个峰），但是洗过的稻草中峰中的水量大于中和的稻草，这表明水洗过的稻草中水的含量更多。比中和后的稻草还大。一种可能的解释是中和作用导致碱溶性组分的沉淀，这些组分充满了孔的体积。

著录项

  • 作者

    Karuna, Nardrapee.;

  • 作者单位

    University of California, Davis.;

  • 授予单位 University of California, Davis.;
  • 学科 Engineering System Science.;Sustainability.;Energy.
  • 学位 M.S.
  • 年度 2013
  • 页码 85 p.
  • 总页数 85
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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