To better elucidate the factors that influence enzyme accessibility (via pretreatment/amorphogenesis) to biomass/cellulose/pulps

点击翻译按钮获取中文摘要

In the proposed work, the specificity of enzymes will be used to assess the potential to make either novel biomaterials (such as nanofibrillated cellulose) or fermentable sugars that could be further processed to various biofuels and biochemicals from biomass. Although the effectiveness of cellulose hydrolysis is often assessed by the amount of soluble sugar released, it is widely acknowledged that the rate limiting step in the overall enzyme-mediated modification/deconstruction of biomass/pulp is creating enzyme access to the cellulosic substrate. In most realistic situations, it is highly probable that cellulose will always be in close association with at least some of the lignin and hemicellulose fractions. At the same time, the fiber, fibril and microfibril structure of a typical biomass substrate will play a role in limiting cellulose accessibility. An ongoing challenge has been to find a reproducible and quantifiable method to quantify enzyme accessibility to the cellulose component and the roles of pretreatment/pulping in combination with appropriate enzyme cocktails to modify/deconstruct cellulosic fibers. Mechanical refining will be assessed as one way of overcoming biomass recalcitrance and opening up the biomass structure. Canada is a major producer of newsprint, produced via mechanical refining, with billions of dollars invested in infrastructure. However, newsprint is a declining market. ***Mechanical refining has been shown to open up the recalcitrant biomass structure by external fibrillation and internal delamination. In the proposed work various pulps, such as northern bleached softwood Kraft pulp (NBSK) will be refined to various extents. Using these types of substrates we hope to minimise the possible influence of lignin and hemicellulose on both fibrillation and hydrolysis and the methods used to try to predict cellulose accessibility. In previous work we and other researchers have used methods such as water retention, microscopy and fiber characterisation, such as aspect ratio, as ways to predict cellulose accessibility and, consequently, the effectiveness of enzyme mediated fibrillation or hydrolysis. However, these methods have tended to provide gross values and are not able to assess possible changes at the microfibril level of cellulose organisation within the fibre. Building on our recent work we will refine the Simon's stain and Carbohydrate-binding modules (CBMs) “probes” methods to better assess cellulose accessibility and the possible mechanisms behind enzyme mediated amorphogenesis of pulps/biomass. The specificity of CBMs make them ideal probes to investigate the microfibril structure of cellulosic substrates. Using optimised pretreatment, enzyme cocktails and novel and established methods for substrate characterisation we hope to better understand cellulose accessibility at the fiber, fibril and microfibril structural levels, with the results contributing to future fibre modification/deconstruction applications.*****