Faculty of Life Sciences, University of Copenhagen, Frederiksberg, Denmark.
Biotechnol Prog. 2012 Nov-Dec;28(6):1478-90. doi: 10.1002/btpr.1617. Epub 2012 Sep 27.
Milliliter scale (ligno)cellulose saccharifications suggest general solute concentration and its impact on water availability plays a significant role in detrimental effects associated with high solids lignocellulose conversions. A microtumbler developed to enable free-fall mixing at dry solids loadings up to 35% (w/w) repeatedly produced known detrimental conversion trends on cellulose, xylan and pretreated lignocellulose with commercial enzymes. Despite this, high concentrations of insoluble nonhydrolysable dextrans did not depress saccharification extents in 5% (w/w) cellulose slurries suggesting mass transfer limitations may not significantly limit hydrolysis extents at high solids loadings. Interestingly, cellulose saccharification by purified cellulases showed increased conversions with increasing dry solids loadings. This prompted investigations into impacts the concentration of soluble species, such as sugar alcohols, low molecular weight enzyme preparation components, and monomer hydrolysis products, have on the hydrolysis environment. Such substances significantly depress conversion rates and were shown to correlatively lower water activity (A(w) ) in the hydrolysis environment while high insoluble solids concentrations did not. Furthermore, low-field NMR on concentrated slurries of insoluble complex carbohydrates, including the nonhydrolysable dextrans, showed all solids constrained water significantly more than high concentrations of soluble species (inhibitory) suggesting water constraint may not be as problematic an issue at high solids loadings compared to the availability of water in the system. Additionally, the introduction of soluble species lessened overall water constraint in high solids systems and appears to shift the distribution of water away from insoluble surfaces. This is potentially a critical issue for industrial processes operating at high dry solids levels.
毫升级纤维素糖化实验表明，溶质浓度及其对水可用性的影响在与高固体含量木质纤维素转化相关的有害影响中起着重要作用。开发了一种微摇床，可在高达 35%（干重）的干固体负荷下实现自由落体混合，该摇床反复使用商业酶对纤维素、木聚糖和预处理木质纤维素产生了已知的有害转化趋势。尽管如此，高浓度不可水解的葡聚糖并没有降低 5%（干重）纤维素悬浮液中的糖化程度，这表明在高固体负荷下，传质限制可能不会显著限制水解程度。有趣的是，纯纤维素酶对纤维素的糖化显示出随着干固体负荷的增加而增加的转化。这促使人们研究可溶性物质（如糖醇、低分子量酶制剂成分和单体水解产物）的浓度对水解环境的影响。这些物质显著降低了转化速率，并表明水解环境中的水活度（A(w)）相应降低，而高不溶性固体浓度则不会。此外，对不可溶性复杂碳水化合物（包括不可水解的葡聚糖）的高浓度悬浮液进行低场 NMR 研究表明，所有固体约束水的程度明显高于高浓度的可溶性物质（抑制性），这表明与系统中的水可用性相比，高固体负荷下水的约束可能不是一个问题。此外，可溶性物质的引入减轻了高固体系统中的整体水约束，并似乎将水的分布从不可溶性表面转移开。这对于在高干固体水平下运行的工业过程来说可能是一个关键问题。
