Optimizing Switchgrass Enzymatic Hydrolysis

For all subsequent experiments described in this paper, AFEX was performed at the estimated optimal conditions determined from the above experiments. The same treatment method was used except that AFEX was performed in a 1.5 l reactor rather than a 22 ml reactor. Between 80 to 150 g dry switchgrass was used for each batch. The amount of switchgrass depended on the ammonia loading, as a practical limitation of the ammonia loading vessel was 160 g. Multiple batches of AFEX treatment were performed, and no significant differences (P < 0.05) were seen in sugar released through enzymatic hydrolysis between batches. All batches were then combined before proceeding with further experiments.
Four commercial enzymatic mixtures were used in these experiments: Accelerase, the b-glucosidase Novozyme 188 (Novozymes, Cambridge, MA, batch no. 058K1144), Multifect Xylanase (Genencor, batch no. 4900805391), and Multifect Pectinase (Genencor, batch no. 4010833580). Enzyme concentrations were determined by nitrogen analysis using a Skalar Primacs SN Total Nitrogen Analyser (Breda, The Netherlands), which uses the Dumas method of combusting all nitrogen to NOx. Enzyme loading varied between 5 to 20 mg/g biomass for Accelerase and 0 to 10 mg/g biomass for the other enzyme mixtures. A total of 48 hydrolysis experiments were run for each type of switchgrass, representing 25 different enzyme combinations determined using the Box-Behnken method [19 (link)]. Hydrolysis was performed in the manner stated above. Results were analysed with Minitab 15 using response surface methodology to determine the importance of each type of enzyme in releasing sugars.