Significant impact of casein hydrolysate to overcome the low consumption of glycerol by Klebsiella aerogenes ATCC 29007 and its application to bioethanol production

As the demand for biodiesel increases, the by-product glycerol is increasing. Biodiesel-derived glycerol is expected to be applied in bioindustries. However, major limitation of industrial fermentation is that the rate of substrate consumption is significantly slower than conventional process. In this study, in order to improve the consumption of refined crude glycerol in Klebsiella aerogenes, casein hydrolysate was supplemented in main medium. As a result, the substrate consumption rate, cell and ethanol concentration were improved about 2.6-fold, 2.5-fold and 3.0-fold, respectively, compared with the control group. In addition, four components of the main medium (peptone, ammonium sulfate, casein hydrolysate, refined crude glycerol) were statistically optimized. The consumption of glycerol was achieved about 89%, and the productivity of bioethanol was found to be 0.83 g/(L h) under the optimized medium. Also, the bioethanol concentration and yield were 15.89 g/L and 0.487 (g/g), respectively. The supplementation of casein hydrolysate had a significant effect on fermentation. It was proved by analyzing the concentration of free amino acids contained in casein hydrolysate. As a result, it was found that glycerol consumption and bioethanol production were promoted by the abundant supply of essential amino acids contained in casein hydrolysate for cell growth. Therefore, these results will be the basis for sustainable development by providing the opportunity to reuse crude glycerol for industrial applications.