BIOTECHNOLOGY - V. H. Herasymenko - 2006

Part II. Specialized Biotechnologies

CHAPTER 10. APPLICATION OF IMMOBILIZED ENZYMES IN BIOTECHNOLOGY

10.3. BIOTECHNOLOGY OF GLUCOSE AND ETHANOL PRODUCTION FROM CELLULOSE

The Development of this technology on a large-scale industrial level is of exceptional economic importance. Intensive research on the Enzymatic Hydrolysis of Cellulose is underway in the USA, Japan, Sweden, Finland, and Italy, and on a smaller scale in Poland, the Czech Republic, Slovakia, and Bulgaria. Driven by the current energy situation, the primary focus is on finding cost-effective ways to produce ethanol as an energy source rather than food-grade glucose. Developing a highly profitable technology for producing ethanol from renewable resources (plant biomass, agricultural, forestry, and industrial wastes) will help alleviate the global energy crisis.

The development of food-grade glucose production technology faces persistent challenges related to the Selection of sources, the quality of cellulose-containing raw Materials, and the enzyme preparations comprising the cellulase complex. Their ratio and activity must be precisely balanced so that the end product of hydrolysis is food-grade glucose rather than a mixture of glucose and other di- and Oligosaccharides unsuitable for the food industry. The hydrolytic degradation of cellulose is carried out by at least four Enzymes that constitute the so-called cellulase complex. It is worth noting the natural occurrence of Enzyme Immobilization, or auto-immobilization. Once firmly adsorbed onto the substrate, the Enzymes of the cellulase complex perform their catalytic function. The products of the hydrolytic reaction are glucose (20-40 %), the disaccharide cellobiose, and a certain amount of more complex oligosaccharides. The COMPOSITION OF THE end products depends on the type of cellulose-containing raw material and the composition and ratio of the enzymes in the cellulase complex.

The sugars formed during the hydrolysis of cellulose can be fermented by Yeast Cell enzymes within the reaction mixture to produce ethanol. Because cellulase complexes capable of directly catalyzing The conversion of cellulose into glucose on an industrial scale are not yet fully optimized, practical efforts are focused on establishing technologies for producing ethanol as an energy source.

All ethanol producers utilize a microbial cellulase complex.

One facility for Processing cellulosic raw materials is operating in the USA on a pilot scale. It produces a cellulase enzyme complex and then uses it to convert waste paper into CARBOHYDRATES, which are subsequently fermented into ethanol using a microbial cellulase system. A second pilot plant—developed cooperatively by Gulf Oil, the University of Pittsburgh, the University of Kansas (USA), and the Japanese company Nippon Mining—is currently refining a biotechnology for producing ethanol from waste paper and agricultural residues.

The hydrolysis of cellulose into glucose can be achieved using the producer Organism Trichoderma reesii, whose cellulase breaks down crystalline and insoluble cellulose. In the USA (S. Albert, 1987), a mutant strain of T. reesii was developed that yields 2 to 4 times more cellulase than the wild-type strain. The cellulose hydrolysis process is straightforward. The fungus is cultivated in a medium containing wood waste and mineral salts, after which the culture is filtered. Shredded paper is added to the enzyme-containing filtrate. The mixture is placed in a reaction vessel and incubated at 50 ^oC under standard atmospheric pressure. The hydrolysis reaction yields a crude glucose syrup, while the unhydrolyzed cellulose and enzymes are recycled for reuse. The glucose yield reaches 50 % of the initial cellulose. According to American experts, converting cellulosic waste into alcohol holds greater promise than producing alcohol from corn starch.