The role of endoglucanase and endoxylanase in liquefaction of hydrothermally pretreated wheat straw

Abstract

The role of endocellulases and endoxylanase during liquefaction and saccharification of hydrothermally pretreated wheat straw was studied. The use of a flow-loop setup with in-line magnetic resonance imaging enabled frequent measurements of viscosity at 55°C during saccharification at 6% total solids content. Viscosity data were complemented with off-line measurements of fiber lengths and release of soluble sugars. A clear correlation between fiber attrition and a decrease in viscosity was found. Fiber lengths and viscosity dropped quickly within the first hour and then stagnated, while sugar yields increased substantially thereafter, illustrating that liquefaction and saccharification are separate mechanisms. Both endoglucanase and endoxylanase were shown to have a significant effect on viscosity during liquefaction while the addition of endoxylanase also increased sugar yield.

A process for energy-efficient high-solids fed-batch enzymatic liquefaction of cellulosic biomass

“…In-line rheological measurements (Maneval et al, 1996;McCarthy et al, 1992;Powell et al, 1994) during hydrolysis were performed in situ and non-invasively using an in-line magnetic resonance imaging (MRI) flow loop as previously demonstrated Skovgaard et al, 2014;Tozzi et al, 2014). An Aspect Imaging 1.03 T permanent magnet with a 0.3 T/m peak gradient strength (Aspect Imaging, Hevel Modi'in Industrial Area, Shoham, Israel) was used to obtain all images used in rheological analyses.…”

“…Velocity profiles as a function of radial position of the flowing biomass slurries were obtained throughout all experiments using a Pulsed Gradient Spin Echo (PGSE) sequence (Maneval et al, 1996;Powell et al, 1994). These velocity profiles, in conjunction with in-line differential pressure measurements, were used to obtain yield stresses during hydrolysis as shown in Tozzi et al and Skovgaard et al (Skovgaard et al, 2014;Tozzi et al, 2014). Yield stresses were thus measured instantaneously and used for process control in the fed-batch setups detailed in Section 2.4.…”

“…We implemented this technique in hydrolysis experiments in fed-batch mode where in situ monitoring of yield stress was used as the control variable to determine the timing and amount of each batch addition. Liquefaction of biomass during enzymatic hydrolysis decreased slurry viscosity to reach a pseudo steady state (Skovgaard et al, 2014;Tozzi et al, 2014), signaling no further significant change in viscosity due to enzyme action, and that the biomass slurry is primed for further additions to reach higher solids contents. Thus, we used the onset of the steady state regime following liquefaction as the indicator for subsequent batch additions.…”

“…Viscosity is a readily measurable bulk-scale variable during enzymatic hydrolysis, and a means to optimize the size and timing of batch additions in situ. In a hydrolysis reaction, viscosity of the biomass slurry reduces rapidly to liquefy the reaction mixture due to endoglucanase activity (Skovgaard et al, 2014;Szijártó et al, 2011;Tozzi et al, 2014). Upon liquefaction, more free water is available in the bulk, which allows for more biomass solids to be added to achieve a higher total solids content.…”

“…We have improved the efficiency of fed-batch saccharification processes by using magnetic resonance imaging (MRI) rheometry of flowing slurries to measure on-going changes in viscosity and yield stress of biomass to obtain time-resolved rheological data during liquefaction Skovgaard et al, 2014;Tozzi et al, 2014). We implemented this technique in hydrolysis experiments in fed-batch mode where in situ monitoring of yield stress was used as the control variable to determine the timing and amount of each batch addition.…”