Metabólitos excretados na fermentação alcoólica como possíveis substratos para o crescimento do gênero <i>Lactobacillus</i>

Abstract

Metabolites excreted in alcoholic fermentation as possible substrates for the growth of the genus Lactobacillus The characteristics of the Brazilian industrial process to produce bioethanol make the distilleries susceptible to the presence of contaminating microorganisms that cause in the fall of production yield. Among the stages of the process, we have the alcoholic fermentation, which consists in the metabolization of sugars by the yeast strain selected from the Saccharomyces cerevisiae species producing the ethanol. At this stage contamination occurs by yeasts of the genus Saccharomyces, yeasts not Saccharomyces and bacteria. The most commonly found bacteria are those belonging to the group of lactic bacteria (LAB), which, because they use different routes to metabolize sugars, are classified as obligate heterofermentative, obligate homofermentative and facultative heterofermentative. Among the genera of this group, Lactobacillus are the most common because of their ability to tolerate high concentrations of ethanol and sugars, high temperatures and low pH. The species L. fermentum and L. plantarum have been reported in several studies as among the most frequent species contaminating this environment. Lactobacillus contaminants are in constant interaction with the yeast strain which consequently has its fermentative efficiency reduced. This work aimed to analyze the metabolites produced during industrial alcoholic fermentation and that can be used by the contaminating bacteria, thus obtaining conditions to be competitive and persistent in the process. For this, two strains were used, isolated from distillery and identified as L. fermentum (I3a) with obligate heterofermentative metabolism and L. plantarum (I4a) with facultative heterofermentative metabolism, presenting a homofermentative metabolism under the conditions studied. Both strains were submitted to growth in the presence of glycerol, malate and pyruvate, which are metabolites produced and excreted by yeast and mannitol produced and excreted by the obligate heterofermentative bacterium. It was observed that the metabolite mannitol is an efficient source of carbon for both strains providing growth even without the presence of sugars. In addition, the combination of glucose, fructose, mannitol and malate was able to increase strains growth. However, the presence of pyruvate presented growth stimulus for the heterofermentative strain. In relation to consumption, the strains were able to metabolize mannitol, malate and pyruvate, however, they did not present glycerol consumption. Thus, both strains are benefited by yeast metabolism and the heterofermentative can reabsorb mannitol when the fermentable sugars are depleted and to make the metabolite available for homofermentative use.

Influência da contaminação bacteriana na fermentação alcoólica de um mosto misto composto por hidrolisado de milho e xarope de cana-de-açúcar para a produção de etanol combustível.

“…Conforme dito anteriormente, a S. cerevisiae dispõe de algumas características que a faz ser amplamente utilizada no meio industrial, como sua tolerância a açúcares, temperatura e teores alcoólicos relativamente elevados na faixa de 8 a 12% durante seu crescimento e até 15% para sua sobrevivência. Tais valores podem variar entre diferentes linhagens (RAPOSO, 2018).…”

“…Alguns tratamentos são propostos pela literatura para conter as contaminações bacterianas, tais como o tradicional uso de antibióticos (CECCATO-ANTONINI, 2018;LEITE, 2011;MUTHAIYAN;LIMAYEM;RICKE, 2011;RICH et al, 2018;SKINNER-NEMEC;NICHOLS;LEATHERS, 2007;LEATHERS, 2004), que têm sido alvo de estudos para ser substituído em decorrência das suas diversas consequências; Outros biocidas químicos (DELLIAS, 2014), alguns compostos naturais (DELLIAS, 2014;LOPES et al, 2016;RAPOSO, 2018) e uso de radiação, que tem apresentado resultados eficazes contra as cepas bacterianas estudadas (ALCARDE; WALDER; HORII, 2003;VALSECHI, 2005).…”