Background: Non-ionic surfactants such as polyethylene glycol (PEG) can increase the glucose yield obtained from
enzymatic saccharification of lignocellulosic substrates. Various explanations behind this effect include the ability of
PEG to increase the stability of the cellulases, decrease non-productive cellulase adsorption to the substrate, and
increase the desorption of enzymes from the substrate. Here, using lignin-free model substrates, we propose that
PEG also alters the solvent properties, for example, water, leading the cellulases to increase hydrolysis yields.
Results: The effect of PEG differs for the individual cellulases. During hydrolysis of Avicel and PASC with a processive
monocomponent exo-cellulase cellobiohydrolase (CBH) I, the presence of PEG leads to an increase in the final glucose
concentration, while PEG caused no change in glucose production with a non-processive endoglucanase (EG). Also,
no effect of PEG was seen on the activity of β-glucosidases. While PEG has a small effect on the thermostability of
both cellulases, only the activity of CBH I increases with PEG. Using commercial enzyme mixtures, the hydrolysis yields
increased with the addition of PEG. In parallel, we observed that the relaxation time of the hydrolysis liquid phase, as
measured by LF-NMR, directly correlated with the final glucose yield. PEG was able to boost the glucose production
even in highly concentrated solutions of up to 150 g/L of glucose.
Conclusions: The hydrolysis boosting effect of PEG appears to be specific for CBH I. The mechanism could be due to
an increase in the apparent activity of the enzyme on the substrate surface. The addition of PEG increases the
relaxation time of the liquid-phase water, which from the data presented points towards a mechanism related to
PEG-water interactions rather than PEG-protein or PEG-substrate interactions.
Keywords: PEG, Surfactants, Enzymatic saccharification of cellulose, Monocomponent cellulase hydrolysis, Avicel
hydrolysis, PASC hydrolysis, Water constraint