Xylan is an important hemicellulosic component of the plant cell wall, serving as a cross linking polymer with lignins.  Xylan is also recognized as a barrier to efficient cellulase action on microfibrils.  A key function of the pretreatment process is the removal of xylan to ensure cost effective production of cell wall sugars for subsequent fermentation. To better understand xylan hydrolysis in corn stover we have studied changes in the distribution of xylan caused by dilute acid pretreatment.

Samples of corn stover rind were labeled with a anti-xylan antibody (LM11) that was conjugated with a fluorescent dye (Alexa Fluor488).  Changes in the distribution of xylan were then monitored using laser scanning confocal microscopy.  We focused on the schlerynchema cells near the vascular bundles for consistency in imaging.  These cells also contain the largest amounts of mass in the stem and are thus of greatest process relevance.

We observed an increase in xylan antibody signal in the middle lamella and lumen that was concomitant with the decrease in the signal from the bulk of the primary and secondary cell walls, throughout the course of pretreatment suggesting that some xylan fractions migrate out of the cell wall before hydrolysis. Furthermore, the signal accumulates and is retained at the middle lamella  and lumen, suggesting that some fractions of the xylan are protected from dilute acid hydrolysis. These latter fractions may be the cause of the slow phase of xylan hydrolysis kinetics reported historically from dilute acid treatment of many bioenergy plant feedstocks.