Bioethanol production from sorghum grain with Zymomonas mobilis: increasing the yield and quality of raw distillates

Abstract

BACKGROUND The present study aimed to demonstrate the superiority of bioethanol yield and its quality from sorghum using the granular starch degrading enzyme Stargen™ 002 over simultaneous saccharification and fermentation, and separate hydrolysis and fermentation using Zymomonas mobilis CCM 3881 and Ethanol Red® yeast. RESULTS Bacteria were found to produce ethanol at higher yield than the yeast in all fermentations. The highest ethanol yield was obtained with Z. mobilis during 48 h of simultaneous saccharification and fermentation (83.85% theoretical yield) and fermentation with Stargen™ 002 (81.27% theoretical yield). Pre‐liquefaction in fermentation with Stargen™ 002 did not improve ethanol yields for both Z. mobilis and Saccharomyces cerevisiae. Chromatographic analysis showed twice less total volatile compounds in distillates obtained after bacterial (3.29–5.54 g L−1) than after yeast (7.84–9.75 g L−1) fermentations. Distillates obtained after bacterial fermentation were characterized by high level of aldehydes (up to 65% of total volatiles) and distillates obtained after yeast fermentation of higher alcohols (up to 95% of total volatiles). The process of fermentation using granular starch hydrolyzing enzyme cocktail Stargen™ 002 resulted in low amounts of all volatile compounds in distillates obtained after bacterial fermentation, but the highest amounts in distillates obtained after yeast fermentation. CONCLUSION The present study emphasizes the great potential of bioethanol production from sorghum with Z. mobilis using granular starch hydrolyzing enzyme Stargen™ 002, which leads to reduced water and energy consumption, especially when energy sources are strongly related to global climate change. © 2023 Society of Chemical Industry.

Bioethanol Production Based on Saccharomyces cerevisiae: Opportunities and Challenges

“…According to the different production raw materials, bioethanol production can be divided into three categories: the use of grain, the use of lignocellulose and the use of algae for bioethanol production [58,59]. There are several microbial cell factories to choose from for fermenting the product ethanol based on different raw materials, including Escherichia coli [60,61], Zymomonas mobilis [62,63], Bacillus subtilis [64,65], S. cerevisiae [66,67], etc. Within all fermentative microorganisms, S. cerevisiae is regarded as an excellent industrial ethanologenic organism based on the outstanding advantages mentioned above.…”