Abstract:
Bioethanol production from cassava starch by B. amyloliquefaciens IFO14141 and S. cerevisiae SKP-01 has been studied. The suitable conditions for growth and starch hydrolysis of B. amyloliquefaciens IFO14141 were as follows; inoculating 7 h - bacterial culture into MSM medium containing 15 g/l of cassava starch and 3 g/l of (NH4)2SO4 at pH 7.0 , incubated on a shaker at 37 oC for 4 h. Yx/s was 0.1774 g cell/g total sugar. The optimal growth condition for seed culture of S. cerevisiae SKP-01 were YPD medium containing 50 g/l glucose , pH 5.0 with shaking at 35oC for 12 h. The maximum specific growth rate was 0.1537 h-1 with 8.23 g/l cell weight. Ethanol production from 15 g/l cassava starch was investigated by inoculating seed culture of yeast into culture medium containing hydrolysed starch after sterilization, followed by glucoamylase hydrolysis for 48 h., resulting in maximum ethanol concentration of 6.03 g/l. In order to increase ethanol yield, 150 g/l of cassava starch was used. The result revealed that maximum ethanol concentration of 21.78 g/l was produced from 95.30 g/l total sugar at 16 h. of cultivation, Yp/s 0.45 g ethanol/g total sugar, equivalent to 88.24 % of theoretical value and productivity 1.36 g ethanol/l.h. Ethanol yield could be increased by inoculating yeast seed culture and glucoamylase into medium containing bacterial hydrolysed starch. The highest viable cell number of bacteria was 9.09 (log CFU/ml) at 22 h and the highest cell number of yeast was 8.21 (log CFU/ml) at 28 h. Ethanol yield obtained by this process was nearly equal to that of the process of inoculating yeast seed culture into medium after sterilization and then adding glucoamylase i.e, the highest ethanol concentration 63.24 g/l (at 22 h. of cultivation) and 63.79 g/l (at 70 h. of cultivation),, the maximum Yx/s 0.48 g ethanol/ g total sugar (at 16 h) and 0.49 g ethanol/ g total sugar (at 64 h of cultivation) equivalent to fermentation efficiency 94.12 and 96.08 % of theoretical values, productivity 2.87 and 0.91 g ethanol/l.h respectively. Bioethanol production by inoculating yeast seed culture and glucoamylase into medium containing bacterial hydrolysed starch after sterilization resulted in increasing ethanol to 66.19 g/l at 46 h, Yx/s 0.48 g ethanol/g total sugar, fermentation efficiency 94.25 % of theoretical value and productivity 1.44 g ethanol/l.h.