Document Type

Thesis - Open Access

Award Date

1983

Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology

Abstract

Approximately 15-20 x 1010 tons of organic plant substance is produced on earth per annum. Half of this material is cellulose. Much of this cellulosic material is highly resistant to breakdown due to other plant components such as lignin and hemicellulose which together with the cellulose contribute to the structural integrity of the plants. Thus, these materials find relatively limited uses in comparison to their abundance. Cellulosic materials are utilized by ruminants as an energy source and in lumber and pulping applications but commercial cellulose processing to produce glucose or glucose derived products is not currently performed. The abundance of cellulosic materials make them attractive as a cheap substrate for industrial applications. However, the conversion of these materials is greatly limited by other protective constituents such as lignin and hemicellulose and by the arrangement of the cellulose molecules themselves. In the past, processes for hydrolysis of cellulose have been primarily based upon the use of acids. These processes proved to be uneconomical. More recent methods have concentrated on the use of microbial cellulases usually in conjunction with pretreatment of the cellulosic materials. The advantages of the enzymatic methods lie in the moderate temperatures for conversion, the noncorrosive nature of the process and quantitative conversion to the desired end product-glucose. The best microbial cellulase producer is the fungus Trichoderma reesei. Trichoderma reesei mutant strains hyperproduce a complete cellulase complex capable of attacking crystalline cellulose and reducing it to glucose. The T. reesei cellulase complex is composed of: S-1, 4-glucan cellobiohydrolases, endo 1, 4-Sglucan glucanohydrolases and a S-glucosidase. Production of T. reesei cellulase is conveniently accomplished in aerated, submerged culture. Trichoderma reesei fermentations on cellulose substrate go through a drop in pH with a subsequent rise at the end of the fermentation. The rise in pH can be used as a general indicator of when to harvest the enzyme. Optimum yields of enzyme require that the acidic phase of the fermentation be maintained between pH 3.0 to 3.5. Yields (in units activity/ml) of enzyme increase with an increase in the cellulose level employed in the production medium. The maximum level is approximately 8% w/v cellulose. Viscosity is a problem in media greater than 8% w/v. The cost of enzyme production is the limiting factor for an enzymatic conversion process. The system of Wilke, Yang and Von Stockar resulted in an enzyme production cost of $0 .05-$0.06/lb. of glucose produced or about 60% of the cost of production. Optimization of cellulase production systems for increased yields are therefore of paramount importance to reduce the cost of enzymatic cellulose conversion. Increased yields and production rates of cellulase have been reported for the use of various additives to the production medium and from advanced culture techniques such as continuous processes. This study involves the production of T. reesei cellulase in a rudimentary production system employing used dairy equipment. The potential for enzyme stimulation by addition of dimethyl sulfoxide to the production medium is also investigated.

Library of Congress Subject Headings

Cellulose

Hydrolysis

Microbial enzymes

Trichoderma

Dimethyl sulphoxide

South Dakota State University Theses

Format

application/pdf

Number of Pages

113

Publisher

South Dakota State University

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