Rohrbach Jessica C, Luterbacher Jeremy S
Laboratory of Sustainable and Catalytic Processing, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland.
Biotechnol Biofuels. 2021 Apr 26;14(1):103. doi: 10.1186/s13068-021-01920-2.
Understanding how the digestibility of lignocellulosic biomass is affected by its morphology is essential to design efficient processes for biomass deconstruction. In this study, we used a model based on a set of partial differential equations describing the evolution of the substrate morphology to investigate the interplay between experimental conditions and the physical characteristics of biomass particles as the reaction proceeds. Our model carefully considers the overall quantity of cellulase present in the hydrolysis mixture and explores its interplay with the available accessible cellulose surface.
Exploring the effect of various experimental and structural parameters highlighted the significant role of internal mass transfer as the substrate size increases and/or the enzyme loading decreases. In such cases, diffusion of cellulases to the available cellulose surface limits the rate of glucose release. We notably see that increasing biomass loading, while keeping enzyme loading constant should be favored for both small- (R < 300 [Formula: see text]) and middle-ranged (300 < R < 1000 [Formula: see text]) substrates to enhance enzyme diffusion while minimizing the use of enzymes. In such cases, working at enzyme loadings exceeding the full coverage of the cellulose surface (i.e. e>1) does not bring a significant benefit. For larger particles (R > 1000 [Formula: see text]), increases in biomass loading do not offset the significant internal mass transfer limitations, but high enzyme loadings improve enzyme penetration by maintaining a high concentration gradient within the particle. We also confirm the well-known importance of cellulose accessibility, which increases with pretreatment.
Based on the developed model, we are able to propose several design criteria for deconstruction process. Importantly, we highlight the crucial role of adjusting the enzyme and biomass loading to the wood particle size and accessible cellulose surface to maintain a strong concentration gradient, while avoiding unnecessary excess in cellulase loading. Theory-based approaches that explicitly consider the entire lignocellulose particle structure can be used to clearly identify the relative importance of bottlenecks during the biomass deconstruction process, and serve as a framework to build on more detailed cellulase mechanisms.
了解木质纤维素生物质的消化率如何受其形态影响对于设计高效的生物质解构工艺至关重要。在本研究中，我们使用了一个基于一组描述底物形态演变的偏微分方程的模型，来研究随着反应进行实验条件与生物质颗粒物理特性之间的相互作用。我们的模型仔细考虑了水解混合物中纤维素酶的总量，并探讨了其与可利用的可及纤维素表面的相互作用。
探索各种实验和结构参数的影响突出了内部传质的重要作用，随着底物尺寸增加和/或酶负载量降低。在这种情况下，纤维素酶向可利用的纤维素表面的扩散限制了葡萄糖释放的速率。我们特别发现，对于小尺寸（R < 300 [公式：见正文]）和中等尺寸（300 < R < 1000 [公式：见正文]）的底物，在保持酶负载量恒定的同时增加生物质负载量应是有利的，以增强酶的扩散，同时尽量减少酶的使用。在这种情况下，在超过纤维素表面完全覆盖的酶负载量（即e > 1）下工作不会带来显著益处。对于较大颗粒（R > 1000 [公式：见正文]），生物质负载量的增加并不能抵消显著的内部传质限制，但高酶负载量通过在颗粒内维持高浓度梯度来改善酶的渗透。我们还证实了纤维素可及性的重要性，其随着预处理而增加。
基于所开发的模型，我们能够提出几个解构工艺的设计标准。重要的是，我们强调了根据木材颗粒尺寸和可及纤维素表面调整酶和生物质负载量以维持强浓度梯度的关键作用，同时避免纤维素酶负载量的不必要过量。明确考虑整个木质纤维素颗粒结构的基于理论的方法可用于清楚地识别生物质解构过程中瓶颈的相对重要性，并作为构建更详细纤维素酶机制的框架。
