2.3. Simultaneous saccharification and ethanol fermentation
The yeastSaccharomyces cerevisiaeYC-097 was used throughout
this study. The stock cultures were maintained on YPD agar plates
at 4C and transferred to fresh plates every 4 weeks to avoid the
micro-organism degradation. The inoculum preparation was by
means of micro-organism transfer from stock cultures to a fresh
plate and grew for 48 h at 30C. Following this period, single colonies were transferred to a 250 mL flask with 100 mL YPD medium.
The flask was placed on a orbital shaker with a shaking diameter
5 cm and a shaking frequency 200 rpm and incubated at 30C for
24 h. This was used as the inoculum for ethanol fermentation, its
yeast concentration is about 1.510
8
cells mL
1
. The ethanol fermentation was carried out in a 250 mL flask with 95 mL ethanol
fermentation medium and 5 mL inoculum at 40C and 200 rpm
for 72 h. During the fermentation, small samples were taken at regular intervals for later analytic usage. The compositions of culture
medium were as follows (g L1
):
The YPD agar medium: D-glucose 20, peptone 20, yeast extract
10, agar 15.
The YPD medium: D-glucose 20, peptone 20, yeast extract 10.
The ethanol fermentation medium: two-step treated RS 100,
peptone 20, yeast extract 10.
The YPD agar medium and the YPD medium were autoclaved at
121C for 20 min after pH was adjusted to 7 by addition of 1 M
NaOH or 1 M HCl. The ethanol fermentation medium was autoclaved at 121C for 30 min after pH was adjusted to 5.5 by
addition of 1 M NaOH or 1 M HCl. Then 150 mg Onazuka R-10
and 5 mL Novozyme 188 were added to 1 L sterilized ethanol
fermentation medium