| Congresso Brasileiro de Microbiologia 2023 | Resumo: 1127-2 | ||||
Resumo:The control of bacterial contaminants in the bioethanol industry is carried out with with sulfuric acid at a pH ranging from 2.5 to 3.0 between fermentation cycles. The cost and danger of handling this acid has attracted research into possible substitutes with the same efficiency. In this context, hydrochloric acid and chlorine dioxide are options that the industry has been testing. In this work, the effect of sulfuric acid, hydrochloric acid and chlorine dioxide was quantified against a bacterium that contaminates the ethanolic fermentation process, Limosilactobacillus fermentum, and against an industrial yeast of Saccharomyces cerevisiae at pH values ranging from 2.0 to 3.0 (for acids) and concentration of 10 to 100 mg/L for chlorine dioxide. The effect of different concentrations of ethanol in combination with acids was also evaluated, since ethanol is present in the cell treatment step and comes together with the centrifuged cell mass after the fermentation cycle, in the range of 3 to 5% v/v. The tests carried out with sulfuric acid show that at pH 2.0 the ethanol concentration does not contribute to the reduction of the bacterial number, since without ethanol there is total loss of bacterial viability. However, at pH 2.5 and 3.0 there is a significant contribution of ethanol to the antiibacterial activity, although there is no difference between the ethanol concentrations. Regardless the ethanol concentration, the best results are obtained at pH 2.5. The time to cause the greatest reduction in the bacterial number in the treatment pH 2.5 + 3% ethanol was 2 h, but there was a drop of 4 log cycles within half an hour of treatment, and there was no difference in the action of the acid + ethanol on bacteria in pure or mixed culture. Using hydrochloric acid, the increase in ethanol concentration leads to a greater reduction in the bacterial number, and in general, hydrochloric acid is less efficient than sulfuric acid, although the reduction in the number of bacteria is significant in the context of ethanolic fermentation. With a half an hour of treatment pH 2.5 + 5% ethanol there was a reduction of about 5 log cycles for the bacterium, whether in pure or mixed culture. Then, there was an even greater reduction in the number of L. fermentum with total loss of viability after 1.5 h of treatment in pure culture, the reduction being smaller when in mixed culture, which reaches 6 log cycles of reduction in number after 2 h. There is no influence of the treatment with both acids with and without ethanol on the yeast. As for chlorine dioxide, the results showed that there is total loss of bacterial viability at concentrations from 20 to 100 mg/L. However, there was a decrease in the yeast number at concentrations of 10 and 20 mg/L (68% and 80%, respectively, after 3 h) and total loss of cell viability with 50 mg/L. At a concentration of 10 mg/L there is a significant reduction in the bacterial number and with 20 and 50 mg/L total loss of cell viability was observed after half an hour of treatment. There is a temporal difference in the effect of chlorine dioxide on bacterium and yeast, as in half an hour the reduction in the bacterial number is already the greatest while for yeast the effect has not yet occurred. In mixed culture, the effect of chlorine dioxide is smaller for both bacterium and yeast. The present work intends to contribute to a better knowledge of this important step of the fermentation process. Palavras-chave: sulfuric acid, hydrochloric acid, chlorine dioxide, yeast, bacteria Agência de fomento:Fapesp, CNPq and Capes | |||||