Kinetics of Enzymatic High-Solid Hydrolysis of Lignocellulosic Biomass Studied by Calorimetry |
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Authors: | Søren N Olsen Erik Lumby Kc McFarland Kim Borch Peter Westh |
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Institution: | 1.Roskilde University, NSM, Biomaterials,Roskilde,Denmark;2.Novozymes Inc.,Davis,USA;3.Novozymes A/S,Copenhagen,Denmark |
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Abstract: | Enzymatic hydrolysis of high-solid biomass (>10% w/w dry mass) has become increasingly important as a key step in the production of second-generation bioethanol. To this end,
development of quantitative real-time assays is desirable both for empirical optimization and for detailed kinetic analysis.
In the current work, we have investigated the application of isothermal calorimetry to study the kinetics of enzymatic hydrolysis
of two substrates (pretreated corn stover and Avicel) at high-solid contents (up to 29% w/w). It was found that the calorimetric heat flow provided a true measure of the hydrolysis rate with a detection limit of about
500 pmol glucose s−1. Hence, calorimetry is shown to be a highly sensitive real-time method, applicable for high solids, and independent on the
complexity of the substrate. Dose–response experiments with a typical cellulase cocktail enabled a multidimensional analysis
of the interrelationships of enzyme load and the rate, time, and extent of the reaction. The results suggest that the hydrolysis
rate of pretreated corn stover is limited initially by available attack points on the substrate surface (<10% conversion)
but becomes proportional to enzyme dosage (excess of attack points) at later stages (>10% conversion). This kinetic profile
is interpreted as an increase in polymer end concentration (substrate for CBH) as the hydrolysis progresses, probably due
to EG activity in the enzyme cocktail. Finally, irreversible enzyme inactivation did not appear to be the source of reduced
hydrolysis rate over time. |
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