Although cassava (Manihot esculenta Crantz) is a potential bioethanol crop, high operational
costs resulted in a negative energy balance in the earlier processes. The present study
aimed at optimizing the bioethanol production from cassava starch using new enzymes
like Spezyme Xtra and Stargen 001. The liquefying enzyme Spezyme was optimally
active at 90 C and pH 5.5 on a 10% (w/v) starch slurry at levels of 20.0 mg (280 Amylase
Activity Units) for 30 min. Stargen levels of 100 mg (45.6 Granular Starch Hydrolyzing Units)
were sufficient to almost completely hydrolyze 10% (w/v) starch at room temperature
(30 1 C). Ethanol yield and fermentation efficiency were very high (533 g/kg and 94.0%
respectively) in the Stargen þ yeast process with 10% (w/v) starch for 48 h. Raising Spezyme
and Stargen levels to 560 AAU and 91.2 GSHU respectively for a two step loading [initial 20%
(w/v) followed by 20% starch after Spezyme thinning]/initial higher loading of starch
(40% w/v) resulted in poor fermentation efficiency. Upscaling experiments using 1.0 kg
starch showed that Stargen to starch ratio of 1:100 (w/w) could yield around 558 g ethanol/
kg starch, with a high fermentation efficiency of 98.4%. The study showed that Spezyme
level beyond 20.0 mg for a 10% (w/v) starch slurry was not critical for optimizing bioethanol
yield from cassava starch, although an initial thinning of starch for 30 min by Spezyme
facilitated rapid saccharificationefermentation by Stargen þ yeast system. The specific
advantage of the new process was that the reaction could be completed within 48.5 h
at 30 1 C.