Zoia Luca, Orlandi Marco, Argyropoulos Dimitris S
Dipartimento di Scienze dell'Ambiente e del Territorio, Università degli Studi di Milano-Bicocca, Piazza della Scienza 1, 20126 Milano, Italy.
J Agric Food Chem. 2008 Nov 12;56(21):10115-22. doi: 10.1021/jf801955b. Epub 2008 Oct 15.
The use of microwaves is explored in an effort to further improve the recently developed lignin isolation protocol termed EMAL (enzymatic mild acidolysis lignin). Because the presence of the lignin-carbohydrate linkages seems to be rather pronounced within wood, a microwave reactor was used to replace traditional refluxing during the mild acidolysis step. This was done in an attempt to augment the selectivity of this step toward cleaving lignin-carbohydrate bonds as well as reducing the overall intensity of this step toward inducing changes in the lignin structure, thus affording lignin in greater yields and purities. Consequently, in this study the yields, purities, and structures of lignins isolated from spruce (softwood) by the EMAL protocol under various microwave conditions were examined. The variables studied included microwave power, microwave heating time, hydrochloric acid concentration and water content of the reaction medium. Microwave heating afforded EMAL samples of high purity (90%, comparable to the conventional protocol) but in significantly greater gravimetric yields. Quantitative (31)P NMR and SEC data confirmed that the structure of lignin was similar to that obtained by traditional EMALs, with comparable contents of beta-aryl ether bonds, phenolic hydroxyls (condensed and uncondensed), and carboxylic acids.
为了进一步改进最近开发的称为EMAL（酶促温和酸解木质素）的木质素分离方案，对微波的使用进行了探索。由于木质素 - 碳水化合物键在木材中的存在似乎相当显著，因此在温和酸解步骤中使用微波反应器代替传统回流。这样做是为了提高该步骤对裂解木质素 - 碳水化合物键的选择性，并降低该步骤对木质素结构诱导变化的总体强度，从而获得更高产率和纯度的木质素。因此，在本研究中，考察了在各种微波条件下通过EMAL方案从云杉（软木）中分离得到的木质素的产率、纯度和结构。研究的变量包括微波功率、微波加热时间、盐酸浓度和反应介质的含水量。微波加热得到的EMAL样品纯度高（90%，与传统方案相当），但重量产率显著更高。定量（31）P NMR和SEC数据证实，木质素的结构与传统EMAL法得到的结构相似，β-芳基醚键、酚羟基（缩合和未缩合）和羧酸的含量相当。
