potentially reduce the cost for the condensation of raw juice.
Considering industrial ethanol fermentation, preservation from
bacterial contamination is quite important, especially the continuous ethanol fermentation [26]. In this study, bacterial contamination did not occur, although sterilization was not conducted.
Using flocculating yeast strain, the continuous ethanol fermentation of thick juice was performed at relative high dilution rate of
0.11 h1. Bacteria without flocculability were washed out at this
high dilution rate. The relative high ethanol concentration of
80 g L1 in R2 inhibited the growth of bacteria. Besides, the undiluted thick juice could be directly fed into the reactors, preventing
the feedstock from bacteria contamination [23]. Flocculating yeast
strain is superior for developing efficient ethanol fermentation
process [9]. The productivity in this study was 8.8 g L1 h1, while it
was 2.3 g L1 h1 in the continuous ethanol fermentation of thick
juice using immobilized yeast cells, and it could not perform at
dilution rate of 0.05 h1 due to intensive yeast leaching from the
support [15]. Ogbonna et al. [14] has reported that immobilization
of flocculating S. cerevisiae strain IR2 (one of the parent strains of
KF-7) onto loofa sponge resulted in ethanol concentration of
approximately 80 g L1 and productivity of (6.2e11.1) g L1 h1 by
using a repeated batch fermentation at 30 C. A carrier for immobilization was used, although the yeast strain was flocculating. In
this study, the similar ethanol concentration and productivity were
obtained without using any carrier for immobilization. Moreover, in
this study the continuous ethanol fermentation was performed at a
higher fermentation temperature of 33 C, which was advantageous standing on the viewpoint of cooling the reactor.
4. Conclusion
This study showed that the flocculating S. cerevisiae strain KF-7
is appropriate for establishing continuous ethanol fermentation
process using sugar beet raw juice and thick juice as feed, with the
advantages of improved productivity and thermotolerant fermentation. Single-stage fermentation was sufficient for sugar beet raw
juice. Two-stage fermentation was proper for sugar beet thick juice.
Although ethanol concentration fluctuated in the second reactor
(R2) due to stress of high ethanol concentration (80 g L1), it was
overcome by feeding fresh yeast cells
potentially reduce the cost for the condensation of raw juice.Considering industrial ethanol fermentation, preservation frombacterial contamination is quite important, especially the continuous ethanol fermentation [26]. In this study, bacterial contamination did not occur, although sterilization was not conducted.Using flocculating yeast strain, the continuous ethanol fermentation of thick juice was performed at relative high dilution rate of0.11 h1. Bacteria without flocculability were washed out at thishigh dilution rate. The relative high ethanol concentration of80 g L1 in R2 inhibited the growth of bacteria. Besides, the undiluted thick juice could be directly fed into the reactors, preventingthe feedstock from bacteria contamination [23]. Flocculating yeaststrain is superior for developing efficient ethanol fermentationprocess [9]. The productivity in this study was 8.8 g L1 h1, while itwas 2.3 g L1 h1 in the continuous ethanol fermentation of thickjuice using immobilized yeast cells, and it could not perform atdilution rate of 0.05 h1 due to intensive yeast leaching from thesupport [15]. Ogbonna et al. [14] has reported that immobilizationof flocculating S. cerevisiae strain IR2 (one of the parent strains ofKF-7) onto loofa sponge resulted in ethanol concentration ofapproximately 80 g L1 and productivity of (6.2e11.1) g L1 h1 byusing a repeated batch fermentation at 30 C. A carrier for immobilization was used, although the yeast strain was flocculating. Inthis study, the similar ethanol concentration and productivity wereobtained without using any carrier for immobilization. Moreover, inthis study the continuous ethanol fermentation was performed at ahigher fermentation temperature of 33 C, which was advantageous standing on the viewpoint of cooling the reactor.4. ConclusionThis study showed that the flocculating S. cerevisiae strain KF-7is appropriate for establishing continuous ethanol fermentationprocess using sugar beet raw juice and thick juice as feed, with theadvantages of improved productivity and thermotolerant fermentation. Single-stage fermentation was sufficient for sugar beet rawjuice. Two-stage fermentation was proper for sugar beet thick juice.Although ethanol concentration fluctuated in the second reactor(R2) due to stress of high ethanol concentration (80 g L1), it wasovercome by feeding fresh yeast cells
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