Browsing by Subject "saccharification"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Characterization of Stem Growth and Chemical Composition in Sorghum Bicolor(2014-03-31) Anderson Jr, Robert TaylorSorghum bicolor is a subtropical grass grown throughout the world for human consumption, animal feed and for the growing biofuels industry. In this thesis I characterize sorghum stem growth and chemical composition, and identify QTL and candidate genes which may regulate stem development. In addition, I attempt to correlate variation in stem composition with saccharification efficiency in two sorghum populations. Under greenhouse conditions, stem length in the vegetative phase typically accelerated starting with the 10th internode, possibly reaching a maximum elongation rate by the time the 20th internode stopped growing. The rate of stem diameter growth increased steadily and achieved a maximum diameter growth rate by the time the 11th internode stopped growing. Under these growth conditions, the plateau for the internode diameter growth rate occurred at 60 days after seedling emergence. Variation in internode growth was driven primarily by cell division, though differences in cell size began to play a significant role as cell number increased. Internode growth was positively correlated with GRAS, bHLH and B3 transcription factor expression and was negatively correlated with AP2/EREBP, MYB and WRKY transcription factors. In addition, the outer rind of the internode had gene expression that resembled expression in young tissue while the central tissue had gene expression that resembled expression in mature tissue. Sorghum accessions displayed a wide range of internode chemical compositions and saccharification efficiencies. However, no clear patterns were present between variation in composition from the NIR spectra and variation in saccharification efficiency on the iWALL system. Multiple linear regression analysis, however, revealed that high biomass density appeared to inhibit saccharification in these populations. Overall, sorghum stem growth mirrors that seen in other monocots. The gene expression information presented here should be useful for future studies on the roles of various transcription factors in plant development and for the identification of transcription factor binding sites within the genome. Such information will be important for future success in molecular breeding and marker assisted selection. This information will also be invaluable for designing genotypes with novel transcripts that can be activated at specific times, in specific organs and under specific conditions.Item Countercurrent Enzymatic Saccharification of Lignocellulosic Biomass and Improvements Over Batch Operation(2014-05-05) Zentay, Agustin NicholasTransportation fuels are the major driver for fossil fuel production, a burden that many countries have tried to ease by blending fossil fuels with biofuel substitutes such as ethanol. Current U.S. ethanol production relies on fermentation of starchy biomass (e.g., corn), which competes with food. Using lignocellulose avoids competition with food; however, it is difficult to digest using traditional batch saccharification. This work investigates countercurrent saccharification as an alternative that reduces enzyme requirements. Compared to baseline yields for standard batch saccharification, countercurrent saccharification reduces enzyme requirements by 5 to 37 times. Initial studies identified Solka-Floc as an acceptable substrate to represent treated biomass; it is readily available and reliably consistent from sample to sample. To measure yields, batch saccharifications were performed at various enzyme loadings and reaction times. Two relatively low enzyme concentrations were selected for further study: 2 and 5 mg protein/g biomass, or 2.6 and 6.4 mg protein/g glucan, respectively. Both of the selected loadings are below levels suggested for commercial use. For each enzyme loading tested, a multi-stage, semi-continuous countercurrent train was constructed. The first experiments used trains consisting of eight 1-L bottles loaded with ?-cellulose, using the same concentrations as the batch experiments. Liquid and solid phases were countercurrently contacted, with transfers of each phase occurring every second day for approximately 4?6 weeks, until steady-state operation was maintained for at least 10 days. At 2 and 5 mg/g enzyme loadings, total sugar yields reached 55.9% and 85.3%, respectively. A follow up study using 16 bottles and 2 mg/g loading produced total sugar yields of 73.4%. In the interest of future scale-up, alternatives to the cycloheximide and tetracycline antibiotic cocktail were investigated. Preliminary results suggest that chloroform or a volatile essential plant oil may be effective. Future work is needed to confirm the antimicrobial strength of these compounds at low concentrations, which is needed to limit enzyme inhibition.