Ethanol productivity from cane molasses by mixed cultures system of Saccharomyces cerevisiae M30 and Kluyveromyces marxianus DMKU 3-1042

Abstract

A renewable energy, ethanol gains more interest because of its benefits such as clean energy and production from biomass fermentation. Industrial fermentation is typically performed using yeast cells. Most of these organisms grow optimally at a temperature range of 25-35°C. On the other hand, ethanol fermentation at high temperature offers many advantages since it can work in a wide temperature range, reduce cooling cost and reduce risk of contamination. The later process, therefore, is suitable for the use in tropical countries, where the average temperature is high throughout the year. Hence, in the present work, ethanol fermentations using thermotolerant yeast, Kluyveromyces marxianus DMKU 3-1042 and Saccharomyces cerevisiae M30 in monoculture and mixed cultures were studied. The cultures in forms of suspended cells and immobilized cells by entrapment within the alginate-loofa matrix (ALM) and adsorption on the fibrous of thin shell silk cocoon were used for the investigation with sugar cane juice/cane molasses as a carbon source at the initial sugar concentration of 220 g/l. The ethanol fermentation by the mixed culture system using thin shell silk cocoon as a carrier was found to be the most effective system. Under batch fermentation in 500 ml Erlenmeyer shaking-flasks, the immobilized mixed culture was found capable of highly efficient ethanol production from both sugar cane juice and cane molasses with the final ethanol concentration of 71.84-80.65 g/l at operating temperature of 37-40°C. Under uncontrolled temperature condition in 1-L continuous packed-bed reactor using the mixed culture immobilized on thin shell silk cocoon fibers, the optimum of productivity (14.18 ±0.06 g/l h) was obtained at 0.21 h-1 of dilution rate with ethanol concentration of 70.88 ±0.31 g/l, whereas, the maximum of ethanol concentration (86.33 ± 1.34 g/l) was obtained at 0.10 h-1 of dilution rate. The immobilized mixed culture was able to remain viable and functioned normally as well as the carrier had good mechanical strength, stability and high potential for the application for long term use. Based on the results of this work, a large scale study is recommended in order to develop an industrial production process.