Abstract:
The objective of the study was to optimize bioethanol production from banana (Kathali
variety) fruit juice using baker’s yeast in order to increase the yield. The banana juice
was inoculated with Saccharomyces cerevisiae (baker’s yeast- 2 g/L) in the fermentation
media composed of 10 g/L yeast extract, 10 g/L KH2PO4, 2 g/L (NH4)2SO4, 2g/L peptone
and 0.5 g/L MgSO4·7H2O and allowed for fermentation for 24 h at room temperature.
When the initial conditions used for the fermentation were 5 g/L of yeast inoculum,
room temperature (30 o
C), shaking speed of 100 rpm for 24 h, the amount of ethanol
produced from the banana juice was 0.8% (v/v). The conditions were optimized
sequentially by changing one factor at a time while keeping the other variables constant
and the condition optimized from each experiment was used in the following
experiment. When different nitrogen sources such as urea, ammonium sulphate,
ammonium carbonate and ammonium nitrate were used in the fermentation media,
highest ethanol production (1.13 times than no nitrogen source) was obtained in the
medium containing ammonium carbonate as nitrogen source. When the amount of
initial yeast inoculum was used as 5 g/L, ethanol yield increased by 1.11 times than the
control which contained the amount of initial yeast inoculum 2 g/L. When the
fermentation temperature was used as 25 °C, ethanol production significantly increased
by 1.2 times than the control. When the rotation speed of the media was used as 150
rpm, ethanol yield increased by 1.08 times than the non-optimized conditions (100rpm).
After the optimization of fermentation time (24 h), inoculum size (0.5 g/100mL),
temperature (25 o
C) and rotation speed (150 rpm), the production of bioethanol was
significantly (p<0.05) increased in Kathali variety of banana juice (1.63 times) than under
the non-optimized conditions.
