Abstract
Bacteria and wild yeasts contamination is usually observed during fuel ethanol fermentation. Moreover, it is known that sucrose (the main carbohydrate in sugarcane juice) is breakdown into glucose and fructose by the yeast enzyme invertase, but hydrolysis is much faster than hexoses metabolism, resulting in monosaccharides accumulation which exerts osmotic stress on yeast and growth of Lactobacillus contaminants. Nonetheless, the knowledge about the effect of invertase enzyme on these contaminants is still scarce, especially because the wort composition can differ from exclusive sugarcane juice to a mixture of juice and molasses. Invertase activity and viability of five strains of Saccharomyces cerevisiae (PE-2, BG-1, CAT-1, FLE and IZ-1904) were quantified and correlated with bacterial contamination in fermentations with biomass recycling. Invertase activity was verified to be, in ascending order: CAT-1 <PE-2 <BG-1 <IZ-1904 <FLE. However, PE-2 and BG-1 were the strains that showed higher ethanol yield (%) in all fermentation cycles except for the first one, and although the yeasts FLE and IZ-1904 exhibited the lowest viabilities, they were not followed by an increase in bacterial proliferation. Thus, the results indicated that the yeast invertase activity does not influence the levels of contamination by Lactobacillus fermentum.
•Invertase activity from different strains was studied during ethanolic fermentation with cell recycling.•The invertase influence on the contamination level by Lactobacilli was investigated.•Ethanol yield, yeasts viability, yeasts budding rate and bacterial contamination were reported.•No differences on the levels of contamination were observed during co-culture fermentation processes.