Ethanol Production from Glycerol Using Immobilized Pachysolen tannophilus During Microaerated Repeated-Batch Fermentor Culture

Abstract

Herein, we established a repeated-batch process for ethanol production from glycerol by immobilized Pachysolen tannophilus. The aim of this study was to develop a more practical and applicable ethanol production process for biofuel. In particular, using industrial-grade medium ingredients, the microaeration rate was optimized for maximization of the ethanol production, and the relevant metabolic parameters were then analyzed. The microaeration rate of 0.11 vvm, which is far lower than those occurring in a shaking flask culture, was found to be the optimal value for ethanol production from glycerol. In addition, it was found that, among those tested, Celite was a more appropriate carrier for the immobilization of P. tannophilus to induce production of ethanol from glycerol. Finally, through a repeated-batch culture, the ethanol yield (Ye/g) of 0.126 ± 0.017 g-ethanol/g-glycerol (n = 4) was obtained, and this value was remarkably comparable with a previous report. In the future, it is expected that the results of this study will be applied for the development of a more practical and profitable long-term ethanol production process, thanks to the industrial-grade medium preparation, simple immobilization method, and easy repeated-batch operation.

Biotechnological production of ethanol: Biochemistry, processes and technologies

“…The last years, there have been a continuously increasing number of reports dealing with the conversion of glycerol into ethanol with the aid of either bacterial or yeast strains (see i.e. ).…”

“…Glucose transporters mediate xylose uptake, but no transporter specific for xylose has yet been identified for the wild-type strains of [58,59]. Finally, in a not very high (but increasing) number of reports, glycerol has been converted into ethanol with the aid of bacterial or yeast strains [60][61][62][63][64][65]. Alcoholic fermentation biochemistry includes substrate degradation pathways (glycolysis, alcoholic fermentation, glyceropyruvic fermentation and respiration for the case of the utilization of hexoses, xylose catabolic pathways for the case of utilization of pentoses and glycerol assimilation and glycolysis for the case of glycerol-converting microorganisms) and regulation between fermentation and respiration (Pasteur effect, Crabtree effect, Kluyver effect and Custers effect) [57,58,66,67].…”

“…Overexpressing genes for aldose (xylose) reductase, xylitol dehydrogenase, xylose isomerase and moderate levels of xylulokinase could potentially enable xylose assimilation and fermentation by genetically engineered S. cerevisiae strains . Finally, in a not very high (but increasing) number of reports, glycerol has been converted into ethanol with the aid of bacterial or yeast strains .…”

“…The most important yeast candidate capable to convert glycerol is the species P. tannophilus . In the yeast cells, two major pathways of glycerol assimilation are implicated; the phosphorylation pathway, that is the most common one and the oxidation pathway.…”