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COLLECTION OF TRICHODERMA REESEI CELLULASE BY FOAMING

Zhang, Qin
http://rave.ohiolink.edu/etdc/view?acc_num=akron1195069754

Abstract Details

2007, Doctor of Philosophy, University of Akron, Chemical Engineering.
Facing the current energy crisis, people try to find alternative energy sources. Certain microbes can ferment soluble sugars to ethanol, which is a well known biofuel. Cellulosic biomass is the most abundant renewable resource. Cellulose can be broken down to soluble sugars by the cellulase enzymes produced only by some microbes. The combination of the above two processes, i.e., break-down of cellulose to sugars and conversion of sugars to ethanol, represents a major approach of solving the energy crisis through renewable biological processes. One of the bottle necks of this approach is the relatively high production cost of cellulase. In this research, the main task was to develop a separation process for cellulase using cost-effective and environment-friendly foam-based techniques. First, the foaming properties of the fermentation broth of Trichoderma reesei RUT C-30 were investigated. The experiment results showed that cellulase was not the dominant substance that caused the foaming of the fermentation broth, although the increase of cellulase concentration in the fermentation process appeared to parallel the increase in foaming tendency. Cellulase concentration was found to be only a weakly positive factor contributing to the foaming whereas the presence of cells and solid cellulose powders had negative effects on foaming. The cell wall was found to be hydrophobic according to the study conducted to observe the cells partition between hydrophobic (organic solvent: n- hexadecane) phase and hydrophilic (aqueous) phase. The finding of hydrophobic cell wall was consistent with the observation that the cells would come out with foam in the foaming study. To prevent the cell from being foamed out of the fermentor during the foaming process intended for cellulase collection, the cell immobilization in small (3mm*3mm*3mm) pieces of polyurethane (PU) foams with different porosity and pore size was also investigated. With some of the PU foam materials, the cells could be effectively immobilized and would not be foamed out during the foaming process. Nevertheless, this system did not function well in the typical stir-tank fermentor: the high shear stress present near the tip of the impeller blades appeared to strip the immobilized cells off the PU foam pellets and caused significant subsequent growth of free (not immobilized) cells in the broth. In a subsequent study of cellulase production using cellulose hydrolysate (CH) as the inducing substrate, it was observed that the addition of the hydrolysate resulted in higher enrichment ratios of cellulase concentration in the collected foamate (over the residual concentration in the spent broth). The foaming study was then expanded to include the addition of other cellulase substrates and substrate analogs, such as xylan hydrolysate (XH) and carboxylmethylcellulose (CMC). The results clearly demonstrated the addition of CH, XH and CMC would improve the enrichment and purification of cellulases by foaming. The improvements were attributed to the affinity binding between the substrates/substrate analogs and the cellulase enzymes and the increased partition of the substrate-enzyme complexes to the foam’s air-liquid interfaces. To further pursue the above affinity foaming phenomenon for significantly improved collection and, potentially, purification of cellulase, a polymeric foaming agent was designed and synthesized. The polymeric surfactant has two parts, one is the hydrophobic region containing methylmethacrylate (MMA) and methacrylic acid (MAA), the other part is cellobiose, i.e., the substrate of the enzyme to bind with during foaming process. Unfortunately, the foaming ability of this synthetic surfactant was not good enough and its synthesis was complicated. As an easier first step, two glycolipid biosurfactants, sophorolipids and rhamnolipids, were investigated as the possible affinity foaming agents. Both glycolipids had a disaccharide moiety that was expected to bind selectively to the â-glucosidase in cellulase. While sophorolipids did not foam well, rhamnolipids showed great foaming ability and selectivity towards â-glucosidase. The enrichment ratio of â-glucosidase activity in the foamate reached up to 20 in the solutions prepared by cellulase powders (from Sigma). The significant benefits of such affinity foam collection and/ or fractionation techniques were clearly shown.
Lu-kwang Ju (Advisor)
178 p.
Engineering, Chemical
CELLULASE; FOAMING; foam; fermentation; broth; Foam fractionation; REESEI

Recommended Citations

Citations

  • Zhang, Q. (2007). COLLECTION OF TRICHODERMA REESEI CELLULASE BY FOAMING [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1195069754

    APA Style (7th edition)

  • Zhang, Qin. COLLECTION OF TRICHODERMA REESEI CELLULASE BY FOAMING. 2007. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1195069754.

    MLA Style (8th edition)

  • Zhang, Qin. "COLLECTION OF TRICHODERMA REESEI CELLULASE BY FOAMING." Doctoral dissertation, University of Akron, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=akron1195069754

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Akron and OhioLINK.