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.