Consistency of Cellulase Activity Assays with Pretreated Biomass Hydrolysis
Cellulase enzymes used for biomass hydrolysis and ethanol production are not measured or valued by volume or weight, but rather by their activity. Cellulase activity is a quantifiable assessment of how effective a given quantity of enzyme is at hydrolyzing its substrate. This assessment is done under a very standard and controlled set of conditions with a well-defined standard substrate. This is necessary for different researchers to compare their results. Although activity is measured with a standard substrate under standard conditions, and enzymes are loaded based on this activity measurement, real conditions and real substrates may be very different.
We have used 4 different commercial cellulase products and tested them all with equal loadings (based on standard activity measurements) using pretreated switchgrass as a model substrate. Dilute Acid and Soaking in Aqueous Ammonia pretreatments were used to test the impact of acidic and alkaline pretreatments, respectively. Enzymes are being tested for sugar yields during hydrolysis alone and with a simultaneous saccharification and fermentation process.
Major Results and Conclusions
We have found that commercial cellulase products do not yield the same concentrations of sugars despite identical loadings on an activity basis. One product consistently showed 10% lower sugar yields under nearly all conditions. These results have been confirmed with both acidic and alkaline pretreatments under a range of pretreatment parameters. Discrepancy in the efficacy of hydrolysis is therefore not likely due to the presence of hemicellulose or lignin alone as the two pretreatments act on different fractions of the biomass. Differences based on enzyme product inhibition will be assessed with the simultaneous saccharification and fermentation testing.