Understanding and Efficiently Manipulating Environmental Stress Caused by Metal Ions to Improve Ethanol Fermentation

Abstract

The inconsistent quality of molasses directly influences ethanol production, particularly due to contamination by metal ions that causes severe problems and reduces production efficiency. This research focused on calcium (Ca2+), potassium (K+), and magnesium (Mg2+) ions that are common in molasses. The key objective was to understand clearly the effect of ions on ethanol fermentation and Saccharomyces cerevisiae performance. Individual ions and ion mixtures were studied in sucrose solution and in molasses. The results showed that severe stress could be ordered as Ca2+>K+>Mg2+ and the adverse effect was greater when the ion concentration increased. Ca2+ was a strong inhibitor while trace amounts of Mg2+ produced a positive effect. To achieve the greatest efficiency in ethanol production using molasses in the substrate preparation, Ca2+ should not exceed 0.18% (w/w) prior to fermentation and the final sugar concentration should be 20–25% (w/v), as adjusting the addition of sucrose will result in a suitable yeast medium. Pretreatment and dilution were the best practices for ion removal, with Ca2+ being clearly decreased. Furthermore, determination of the composition and ion concentration in molasses are essential initial steps that must be routinely applied to ensure that the knowledge gained and the efficient techniques investigated can both be used to improve ethanol production.