earticle

영어

Ethanol is used as a preservative in gochujang, a Korean traditional condiment. The aim of this study was to optimize the medium components and process conditions for improved production of ethanol by osmophilic yeast Zygosaccharomyces rouxii isolated from gochujang. Statistical experimental methods were used to optimize the production medium components in shake flasks. Preliminary experiments identified the best sources of carbon, nitrogen, phosphorous, metal ion and salt. The Plackett-Burman design method identified glucose, yeast extract and magnesium sulfate as critical components of the medium influencing ethanol production by Zygosaccharomyces rouxii. In order to enhance further the production of ethanol the response surface methodology (RSM) was used. The concentrations of medium components for improved ethanol production were as follows (g/L): glucose 158 (15.8%); yeast extract 13.6 (1.36%); magnesium sulfate 2.04 (0.2%), potassium dihydrogen phosphate 1, 5; calcium chloride 0.2. This optimization resulted in 50.4 g/L of ethanol in shake flasks. Ethanol production was further studied in in a 2.5 L laboratory fermentor in batch and repeated batch mode using the RSM optimized medium. Effects of fermentation conditions (temperature, pH, agitation rates) on ethanol production were investigated and the optimum process conditions were found to be 29℃, pH 5 and 200 rpm yielding 66.7 g/L ethanol (91% yield) at 60 hours . The optimized process conditions further improved ethanol production by a factor of 1.3. Repeated batch fermentation using the optimized medium and optimized fermentation conditions produced high ethanol levels in all the four cycles studied and reached 54.2 g/L at 210 hours, a good indication that the osmophilic yeasts were still stable and have great industrial potential in the ethanol industry.