Abstract
<em>Kluyveromyces marxianus</em> 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 <em>K. marxianus</em> 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 <em>K. marxianus</em> 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).
Highlights
The production of ethanol using crops is increasing rapidly and is causing considerable concern that this may limit the supply of food in the future
The results suggested that strain Thailand Institute of Scientific and Technological Research (TISTR) 5925 belongs to K. marxianus
The results identified using response surface methodology (RSM) in the current paper provide the optimum conditions for ethanol production from cassava pulp
Summary
The production of ethanol using crops is increasing rapidly and is causing considerable concern that this may limit the supply of food in the future. Lignocellulosic biomass such as agricultural residue is an alternate, inexpensive source of fermentable sugars [1]. Cassava pulp is mainly used for animal feed and fertilizer, it could be used to produce fuel ethanol, obviating the need to compete with food crops. The growth temperature range for S. cerevisiae optimal for fuel ethanol fermentation is 30–35 °C [8]. C. tropicalis of cassava pulp was used in a simultaneous saccharification and fermentation (SSF) process at 40 C, but the reported ethanol concentration was low (1.4% w/v) [6]
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