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

Szambelan K, Szwengiel A, Nowak J, Frankowski J, Jeleń H

Published: 5 May 2023 in Journal of the science of food and agriculture
Keywords: Zymomonas mobilis, fermentation, granular starch, sorghum grains, volatile by-products
Pubmed ID: 37144348
DOI: 10.1002/jsfa.12688

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.