Biomass water interactions as a tool for explaining the recalcitrance of pretreated materials: towards a fundamental understanding of water in bioprocesses

Water functions as both reaction medium, co-substrate, and product diluent in the biochemical production of lignocellulosic biofuels and other bioprocesses.  It is therefore important to understand how different methods of biomass pretreatment impact the relationship between water and biomass, and the effect on enzymatic hydrolysis.   We present data showing a general correlation between a biomass’s ability to retain and restrict water, and enzymatic hydrolysis yields, pointing towards a global measurement of biomass recalcitrance.  In this study we combine for the first time measurements of water retention and restriction by water retention value (WRV) determination and low field Nuclear Magnetic Resonance (NMR) relaxometry to give new understanding to the interactions between water and pretreated biomass.  A number of different feedstocks were pretreated at different severities and chemistries, and were analyzed for their enzymatic hydrolyzability, NMR water restriction profiles, and water retention value. We found a general correlation between the WRV, the restriction of water by the biomass, and the enzymatic hydrolyzability of the material.  Glucose yields after enzymatic hydrolysis were found to increase with WRV and with increased water restriction as measured by NMR. This is in line with previous results from water restriction measurements on pure cellulose. Recent work in our group has also shown that non-cellulose plant cell wall polymers present during hydrolysis affect hydrolysis yields not only by blocking access to cellulose, but also by changing water restriction. These techniques may be a useful tool for comparing pretreated materials regarding their suitability for hydrolysis at high solids concentrations.