Cellulose crystallinity index: measurement techniques and their impact on interpreting cellulase performance.
Cellulose crystallinity index: measurement techniques and their impact on interpreting cellulase performance.
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DOI：
10.1186/1754-6834-3-10
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发表时间：
2010-05-24
影响因子：
6.3
通讯作者：
Johnson DK
中科院分区：
文献类型：
--
作者：
Park S;Baker JO;Himmel ME;Parilla PA;Johnson DK
虽然结晶度指数（CI）的测量具有很长的历史，但是已经发现CI根据测量方法的选择而显著变化。在这项研究中，四种不同的技术，结合X射线衍射和固态13 C核磁共振（NMR）进行了比较，使用八种不同的纤维素制剂。我们发现，最简单的方法，这也是最广泛使用的，它只涉及测量两个高度的X射线衍射图，产生显着更高的结晶度值比其他方法。所用纤维素制剂（Avicel PH-101）的文献数据支持这一观察结果。我们认为，这里提出的替代X射线衍射（XRD）和NMR方法，考虑了无定形和结晶纤维素对整个XRD和NMR光谱的贡献，提供了一个更准确的测量纤维素的结晶度。尽管具有高无定形含量的纤维素通常更容易被酶消化，但基于文献中发表的研究，尚不清楚CI是否实际上提供了纤维素样品消化率的明确指示。纤维素可及性应受结晶度的影响，但也可能受几个其他参数的影响，如木质素/半纤维素含量和分布，孔隙率和粒度。考虑到纤维素CI值的方法依赖性以及纤维素酶与无定形和结晶纤维素相互作用的复杂性质，我们警告不要试图将CI中相对较小的变化与纤维素消化率的变化相关联。此外，基于低水平的纤维素转化率对纤维素酶性能的预测可能不包括有意义的结晶组分的充分消化。
Although measurements of crystallinity index (CI) have a long history, it has been found that CI varies significantly depending on the choice of measurement method. In this study, four different techniques incorporating X-ray diffraction and solid-state 13C nuclear magnetic resonance (NMR) were compared using eight different cellulose preparations. We found that the simplest method, which is also the most widely used, and which involves measurement of just two heights in the X-ray diffractogram, produced significantly higher crystallinity values than did the other methods. Data in the literature for the cellulose preparation used (Avicel PH-101) support this observation. We believe that the alternative X-ray diffraction (XRD) and NMR methods presented here, which consider the contributions from amorphous and crystalline cellulose to the entire XRD and NMR spectra, provide a more accurate measure of the crystallinity of cellulose. Although celluloses having a high amorphous content are usually more easily digested by enzymes, it is unclear, based on studies published in the literature, whether CI actually provides a clear indication of the digestibility of a cellulose sample. Cellulose accessibility should be affected by crystallinity, but is also likely to be affected by several other parameters, such as lignin/hemicellulose contents and distribution, porosity, and particle size. Given the methodological dependency of cellulose CI values and the complex nature of cellulase interactions with amorphous and crystalline celluloses, we caution against trying to correlate relatively small changes in CI with changes in cellulose digestibility. In addition, the prediction of cellulase performance based on low levels of cellulose conversion may not include sufficient digestion of the crystalline component to be meaningful.
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