Abstract
We developed the intensive multiple sequential batch simultaneous saccharification and cultivation of the selected thermotolerant yeast strain for single-step ethanol production. The selection and high-cell-density inoculum production of thermotolerant yeast able to produce ethanol under the optimal conditions for single-step ethanol fermentation has become a necessity. In this study, the newly isolated Kluyveromyces marxianus SS106 could tolerate high temperatures (35–45 °C) and grow under a wide range of pH values (3.0–5.5), which are the optimum conditions of raw cassava starch hydrolyzing enzyme used in single-step ethanol fermentation. The high-cell-density concentration of K. marxianus SS106 was produced by a single batch and an intensive multiple sequential batch process in a 5-L stirred tank bioreactor using the simultaneous saccharification and cultivation (SSC) method. The single SSC process yielded the yeast cell biomass at a concentration of 39.30 g/L with a productivity of 3.28 g/L/h and a specific growth rate of 0.49 h−1. However, the yeast cell density concentration was higher in the intensive multiple sequential batch SSC than in the single batch process. This process yielded yeast cell biomass at concentrations of 36.09–45.82 g/L with productivities of 3.01–3.82 g/L/h and specific growth rates of 0.29–0.44 h−1 in the first six batch cycle. The results suggested that the intensive multiple sequential batch simultaneous saccharification and cultivation of K. marxianus SS106 would be a promising process for high-cell-density yeast production for use as the inoculum in single-step ethanol fermentation. Furthermore, we also experimented with single-step ethanol production from raw cassava starch by K. marxianus SS106 in a 5-L stirred tank fermenter. This produced ethanol at a concentration of 61.72 g/L with a productivity of 0.86 g/L/h.
Highlights
One of the problems associated with the conventional process for ethanol production based on cassava starch raw material is the different optimum temperatures for liquefaction, saccharification, and fermentation
We looked for an appropriate yeast strain for the single-step ethanol production using a combination of raw starch hydrolysis and fermentation
The screening of thermotolerant yeast from industrial and natural resources in tropical regions is suitable for ethanol fermentation at high temperatures [17]
Summary
One of the problems associated with the conventional process for ethanol production based on cassava starch raw material is the different optimum temperatures for liquefaction, saccharification, and fermentation. This process requires high energy consumption because starch hydrolysis takes place at high temperatures that require enormous amounts of steam and an efficient water-based. To improve the ethanol production process from starchy materials, single-step ethanol production using a combination of raw starch hydrolysis and fermentation was developed here. This process used granular starch hydrolyzing enzyme and free cells of yeast at the same time for reducing the cost of energy input and fermentation time from multistage operation. K. marxianus is the fastest growing yeast, with a maximum growth rate of 0.80 h−1 , and S. cerevisiae is only 0.37 h−1
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
