Kluyveromyces marxianus TISTR 5925, isolated from rotten fruit in Thailand, can ferment at pH 3 at temperatures between 42 and 45 ℃. Bioethanol production from cassava pulp using the simultaneous saccharification and fermentation (SSF) process was evaluated and compared with the separated hydrolysis and fermentation (SHF) process using K. marxianus TISTR 5925. The ethanol concentrations obtained from the SSF process were higher than those from the SHF process. The optimum conditions for ethanol production were investigated by response surface methodology (RSM) based on a five level central composite design involving the following variables: enzyme dilution (times), temperature (℃) and fermentation time (h). Cassava pulp was pretreated by boiling for 10 min, treated with a mixture of enzymes (cellulase, pectinase, α-amylase and glucoamylase), then fermented by K. marxianus TISTR 5925. Data obtained from the RSM were subjected to analysis of variance and fit to a second order polynomial equation. At optimum enzyme dilution (0.1 times), temperature (41 ℃) and fermentation time (27 h), the maximum obtained concentration of ethanol was 5.0% (w/v), which is very close to the predicted ethanol concentration of 5.3% (w/v).
