Cell treatment in ethanolic fermentation: a study of the effect of conventional and unconventional strategies on Limosilactobacillus fermentum, fermentative parameters, cell autolysis, viability and gene expression of Saccharomyces cerevisiae

Abstract

During alcoholic fermentation to produce fuel ethanol, the use of acid treatment to combat bacterial contamination is a very common practice in Brazilian units. An aqueous solution of sulfuric acid at a pH ranging from 2.0-2.5 is used for a period of two hours, causing a significant reduction in the number of bacterial cells and promoting the deflocculation of the yeast caused by both bacteria and an intrinsic characteristic of the process yeast. In recent years, distilleries have used chlorine dioxide to fully or partially replace sulfuric acid, with a number of advantages over acid. Despite being a common practice in ethanol production units in Brazil, little is known about the effects of cell treatment on yeast metabolism and morphology and on fermentative parameters, highlighting the cellular autolysis process that can occur with bacteria, releasing substances that can stimulate or inhibit fermentation and yeast. The present project proposes to carry out a more in-depth study of conventional yeast treatment strategies, such as the use of sulfuric acid and chlorine dioxide, and to evaluate non-conventional strategies with potential for industrial use, such as hydrochloric acid, addition of ethanol to sulfuric acid and chitosan, a biopolymer extracted from shrimp waste. The focus of the work will be to evaluate the efficiency of each treatment on the bacterium Limosilactobacillus fermentum, one of the main contaminating bacteria of the fermentation process, and on the yeast of the process, Saccharomyces cerevisiae (industrial strain PE-2), analyzing the microbial morphological changes, occurrence of bacterial autolysis, yeast gene expression and fermentation parameters. It is expected with this work to have an action profile of conventional treatments and to evaluate new strategies that can be indicated for the industrial process, aiming at greater efficiency, lower cost, less environmental impact with less use of substances potentially toxic to the environment and the operator. (AU)