The liquid fraction after microwave pretreatment was not
hydrolysed further with enzymes, but directly fermented to
ethanol. A mixed culture with S. cerevisiae and Z. mobilis in a
ratio of 10 g L1 to 5 g L1 was used to ferment the hydrolysate
obtained after microwave pretreatment in an acid solution.
Fermentation was conducted in an incubator at 32 C at a pH
of 4.5 for 24 h. The conversion of total sugars in the broth to
ethanol over time as well as the optical density of the cell
present in the broth is shown in Fig. 6.
An ethanol yield as high as 480 g kg1 was obtained, which
translate to a conversion efficiency of 94%. This also implies
that both pentose and hexose sugars were converted to
ethanol. The optical density as reported in Fig. 6 is for both
fermenting organisms as UV spectroscopy cannot distinguish
between S. cerevisiae and Z. mobilis.