Very high Gravity (VHG) Bioethanol Production Using Modified Simultaneous Saccharification and Fermentation of Raw Cassava Chips with Molasses by Kluyveromyces marxianus DMKU-KS07

Abstract

Purpose: The aim of this study was to investigate the enhancement of very high gravity (VHG) bioethanol production using co-substrates of cassava chip hydrolysates and molasses by Kluyveromyces marxianus DMKU-KS07. Methods: The factors effecting cassava chip hydrolysis by raw starch degrading enzyme (RSDE) from the thermophilic bacterium Laceyella sacchari LP175 and commercial glucoamylase were investigated. The obtained raw cassava chip hydrolysate was co-fermented with molasses by the thermotolerant K. marxianus DMKU-KS07 at 42°C under nonsterile system. Results: Factors affecting sugar syrup production from raw cassava chips by synergistic hydrolysis and enzyme saccharification were optimized at temperature, substrate concentration and agitation rate of 50 °C, 250 g/L and 200 rpm, respectively. A yield of 98.6 g/L was obtained at 6 h of incubation, equivalent to 45.9% saccharification and 51.4% hydrolysis of starch, respectively. High bioethanol concentration at 118 g/L, with highest productivity of 2.19 g/L/h and ethanol yield (YP/S) at 0.44 g EtOH/g total sugar, equivalent to 86.3% theoretical yield, was obtained by modified simultaneous saccharification and fermentation (Modified SSF) with co-fermentation of substrates from the enzymatic hydrolysates of raw cassava chips at 42 °C for 12 h. Subsequent addition of molasses increased the final concentration to 100 g total sugar/L at 36 h. Conclusions: Co-fermentation of raw cassava chip hydrolysates with molasses enhanced production of bioethanol at VHG condition, and showed potential for application in ethanol production by enhancing the fermentation process and reducing energy consumption.