Production of fructose and ethanol by selective fermentation of glucose-fructose mixtures.

Production of fructose and ethanol by selective fermentation of glucose-fructose mixtures.

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Title: Production of fructose and ethanol by selective fermentation of glucose-fructose mixtures.
Author: Koren, David W.
Abstract: In this project the selective conversion of glucose to ethanol from glucose/fructose mixtures was investigated. The process was carried out using a mutant of Saccharomyces cerevisiae, batchwise, continuously with immobilized cells and semicontinuously. The kinetic behaviour of S. cerevisiae ATCC 36859 was studied using batch fermentation data. The growth of the yeast is inhibited equally by glucose and fructose, even though fructose is not consumed by the yeast. Fermentation models were formulated in this work. These models include terms which account for the inhibition of growth, glucose consumption and ethanol production by the carbohydrate and ethanol. The models predict that the growth rate of the yeast will be zero if the medium contains either 488 g/L total carbohydrates of 62 g/L ethanol. Batch tests were carried out with hydrolyzed Jerusalem artichoke juice and High Fructose Corn Syrup. An ethanol productivity of 21 g/Lh was attained in a batch process using an initial biomass concentration of 94 g/L. It was found though that this process suffered from the inhibitory effects of high total carbohydrate concentrations, therefore products containing high fructose concentrations were produced with lower ethanol productivities. In addition, reuse of the biomass resulted in a reduction of 40% in its activity. The cells were immobilized in calcium alginate beads and placed in a tubular reactor. In this form they were used for more than 1000 hours without a loss of activity. A syrup containing fructose as 99% of the reducing sugars was produced from synthetic as well as from food grade glucose/fructose mixtures. A maximum ethanol productivity of 13 g/Lh was attained. A product containing 76 g/L ethanol was also produced in this process. The productivity of the reactor was reduced as the total carbohydrate concentration was increased, therefore products with a high fructose concentration ($>$150 g/L) could not be formed without a significant drop in the productivity using the immobilized cells. The inhibitory effects of high total carbohydrate concentrations were reduced by using a fed batch process. In this scheme, 42 High Fructose Corn Syrup was used with and without added nutrients as the feed solution; sterilization of the syrup was not necessary due to its high solids concentration. The syrup was continuously fed to a bioreactor, the glucose was converted to ethanol while the fructose accumulated. A syrup containing 257 g/L fructose and 68 g/L ethanol was produced in this process. The product formed in the process was purified with activated carbon and ion-exchange resin. A clear and colourless fructose syrup that visibly resembled HFCS was produced. The ethanol in the product allowed for storage of the product for long periods of time before its further treatment. (Abstract shortened by UMI.)
Date: 1991
URI: http://hdl.handle.net/10393/7944

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