The effect of the dilution rate on the continuous ethanol
fermentation of raw juice was carried out at 30 C by using singlestage
fermentation. As shown in Fig. 4A, there were no significant
changes in ethanol concentration, yeast cell viability and residual
sugar concentration by increasing dilution rate from 0.1 h1 to
0.3 h1. The concentration of acetic acid was below 1500 mg L1,
and the concentration of lactic acid was between 4500 mg L1 and
11 000 mg L1 in the reactor due to its abundance in the feedstock
as shown by horizontal lines in Fig. 4B. Neither acetic acid concentration
nor lactic acid concentration significantly increased
comparing with these in feedstock. Judging from the changes of
VFAs concentrations and residual sugar concentration, therewas no
serious bacterial contamination. Although the lactic acid concentration
reached approximately 9 g L1 in the reactor, ethanol
fermentation was not inhibited at all, indicating that the yeast
strain KF-7 is lactic acid-tolerant. By increasing the dilution rate
from 0.1 h1 to 0.3 h1, the productivity markedly increased from
(6.2 ± 0.2) g L1 h1 to (19.9 ± 0.5) g L1 h1. This result was in
accordance with the results of our previous studies, in which
kitchen garbage [17], sweet sorghum juice [18], acid hydrolysate of
wood biomass [19] and molasses [22] were the feedstock.