Intensive Multiple Sequential Batch Simultaneous Saccharification and Cultivation of <i>Kluyveromyces marxianus</i> SS106 Thermotolerant Yeast Strain for Single-Step Ethanol Fermentation from Raw Cassava Starch

• Main Authors: Kwanruthai Malairuang, Morakot Krajang, Rapeepong Rotsattarat, Saethawat Chamsart
• Format: Article
• Language: English
• Published: MDPI AG 2020-07-01
• Series: Processes
• Subjects: simultaneous saccharification and cultivation (SSC); intensive multiple sequential batch cultivation; thermotolerant yeast; <i>Kluyveromyces marxianus</i>; ethanol production
• Online Access: https://www.mdpi.com/2227-9717/8/8/898

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 <i>Kluyveromyces marxianus</i> 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 <i>K. marxianus</i> 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 <i>K. marxianus</i> 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 <i>K. marxianus</i> 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.