16-03: Physical factors limiting bioconversion at high solids: the role of water

In a high solids bioconversion setting, low water accessibility can affect enzyme performance. It is hypothesized that different pools of water have different functions during hydrolysis; e.g. water present inside the cell wall matrix may play a different role than water in the lumens. By characterizing these different states of water, a better fundamental understanding of the relationship between water and biomass can be achieved. Using low-field NMR relaxometry, different states of water (cell wall vs. lumen) during cellulose hydrolysis at high solids loadings (33 wt%) were detected based on differences in T₂ relaxation times. Two separate compounds were used to tag these states: heavy water (D₂O) and oleyl alcohol (a non-polar and non-miscible compound with similar viscosity as water). The former is not detectable by LF-NMR but is involved in the hydrolysis process while the latter is detectable by LF-NMR but does not participate in hydrolysis. Sugar quantification was also done to test whether isotopic or oleyl alcohol substitution affected enzyme performance. The LF-NMR technique allows us to monitor the exchange between the states of water and determine how each state changes over the course of hydrolysis. Thus, it would be possible to determine which pool of water is most accessible to the enzyme. In order to identify to what extent these states of water are involved during hydrolysis, samples with water only, active enzyme, and inactive enzyme were compared.