Isoamyl Alcohol and Isobutanol Production from Sugarcane Molasses Fermentation at a Microdistillery: pH, Supplementation, and Refrigeration Effects

Fusel oil, a byproduct of ethanol fermentation, mainly consists of isoamyl alcohol and isobutanol. These compounds negatively impact distillation by causing fouling and corrosion in rectification columns, increasing maintenance costs, and affecting ethanol quality and sensory properties. Despite these drawbacks, fusel oil has extensive applications in the fine chemical industry. Its quality and yield vary depending on raw materials and fermentation conditions. This research investigates the effects of pH, supplementation, and refrigeration on isoamyl alcohol and isobutanol formation during sugarcane molasses fermentation at a microdistillery. Fermentations were performed in fed-batches with molasses must at 25 °Brix and commercial dry yeast (25% v/v) for 10 h. A complete 2³ factorial design analyzed the effects on fermentation efficiency (nf ), process efficiency (np), ethanol productivity (P), substrate-to-cell conversion (YX/S), isoamyl alcohol production (A), isobutanol production (B), and the A/B ratio. Statistical analysis included analysis of variance (ANOVA) and Tukey’s test. Results showed significant interactions influencing isoamyl alcohol and isobutanol production and the A/B ratio. Fermentation at pH 3.5, without supplementation, and with refrigeration achieved the highest A/B ratio (2.26). Conversely, fermentation at pH 5.0, with supplementation, and without refrigeration, yielded the highest isoamyl alcohol (0.4372 g L-1) and isobutanol (0.2666 g L-1) concentrations, without selectively enhancing isoamyl alcohol.