Fermentation conditions
Saccharomyces cerevisiae 5019 was
obtained from Bangkok MIRCEN. It was
maintained at 4°C on slants of Sabouraud agar.
Inocula of S. cerevisiae was grown on glucose in
Erlenmeyer flasks at 30°C on a rotary shaker at
150 rpm for 24 h. The inoculum medium was
composed of 20 g/l glucose, 1 g/l yeast extract, 1 g/
l MgSO4
•7H2O, 2 g/l (NH4)2SO4, and 0.5 g/l
KH2PO4. Sugar solution was autoclaved separately.
The batch fermentations were carried at 30°C on a
rotary shaker at 150 rpm for 18 h in 250 ml
Erlenmeyer flask. The working volume was 50 ml
of synthetic medium. The synthetic medium
composed of 1 g/l yeast extract, 1 g/l MgSO4
•7H2O,
2 g/l (NH4)2SO4, 0.5 g/l KH2PO4 and the carbon
source 20 g/l glucose or cassava peel hydrolysate
from diluted sulfuric acid hydrolysis.
The hydrolysate was neutralized to pH 7.0
using NaOH for fermentation process, then the
hydrolysate was filtered through 0.2 mm membrane.
The treated hydrolysate was supplemented with
nutrients (1 g/l yeast extract, 1 g/l MgSO4
•7H2O, 2
g/l (NH4)2SO4, and 0.5 g/l KH2PO4). The fermentation
was carried out at 30°C for 18 h. The fermentation
broths were filtered through a 0.45ºm
Millipore filter. Ethanol in the samples was
determined by gas chromatograph using a 60:80
Carbopack B: 5% Carbowax 20 M glass column.
The injector was operated at 200°C. The flame
ionization detector (FID) was kept at 200°C.
Nitrogen gas was used as carrier gas at a flow rate
of 30 ml/min. The temperature was programmed at
120°C for 1.4 min, from 120°C to 240°C at 30°C/
min, then held 5 min at 240 °C.
Biomass concentrations were determined
by dry cell weight, whereby 3 x 10 ml samples were
filtered through a membrane filter, washed twice by
distilled water, dried at 104°C for 24 h and weighted