Homo- and heterofermentative lactobacilli differently affect sugarcane-based fuel ethanol fermentation

Abstract

Bacterial contamination during industrial yeast fermentation has serious economic consequences for fuel ethanol producers. In addition to deviating carbon away from ethanol formation, bacterial cells and their metabolites often have a detrimental effect on yeast fermentative performance. The bacterial contaminants are commonly lactic acid bacteria (LAB), comprising both homo- and heterofermentative strains. We have studied the effects of these two different types of bacteria upon yeast fermentative performance, particularly in connection with sugarcane-based fuel ethanol fermentation process. Homofermentative Lactobacillus plantarum was found to be more detrimental to an industrial yeast strain (Saccharomyces cerevisiae CAT-1), when compared with heterofermentative Lactobacillus fermentum, in terms of reduced yeast viability and ethanol formation, presumably due to the higher titres of lactic acid in the growth medium. These effects were only noticed when bacteria and yeast were inoculated in equal cell numbers. However, when simulating industrial fuel ethanol conditions, as conducted in Brazil where high yeast cell densities and short fermentation time prevail, the heterofermentative strain was more deleterious than the homofermentative type, causing lower ethanol yield and out competing yeast cells during cell recycle. Yeast overproduction of glycerol was noticed only in the presence of the heterofermentative bacterium. Since the heterofermentative bacterium was shown to be more deleterious to yeast cells than the homofermentative strain, we believe our findings could stimulate the search for more strain-specific antimicrobial agents to treat bacterial contaminations during industrial ethanol fermentation.

Ethanol production in Brazil: a bridge between science and industry

“…Furthermore, heterofermentative bacteria also produce mannitol which has been used as an indicator of sugarcane deterioration by microorganisms as well as of contamination of alcoholic fermentation processes by heterofermentative bacteria 89, 90. Homo and heterofermentative lactic acid bacteria can affect the fermentation of different ways 91 . Because of their importance, some distilleries have monitored mannitol, lactate, acetate and residual sugars in wine through high performance liquid chromatography improving their process control 29 …”

Agro-industrial wastes as sources of bioactive compounds for food and fermentation industries

“…Shirahigue & Ceccato-Antonini fermentum and L. plantarum (TABASCO et al, 2011), which are the common contaminants of the bioethanol industry process (BASSO et al, 2014). Grape extracts have been reported as more effective against bacteria than yeasts; and consequently, the results obtained with lactic acid bacteria are shown to be very promising for application in the ethanol fuel industry.…”

Caracterização da comunidade bacteriana contaminante do processo fermentativo para produção de etanol e o impacto no metaboloma da fermentação

“…cerevisiae CAT-1 contaminada com L. fermentum (I-2) em dois níveis de infecção, de 10 6 e 10 8 UFC/mL, foi observado que não houve alteração para a taxa de viabilidade e brotamento das leveduras (dados não apresentados). Cherubin (2003) e Basso et al (2014) as BALs têm uma capacidade limitada de produzir aminoácido utilizando fontes inorgânicas de nitrogênio (AXELSSON, 2004).…”

“…Os valores de NIST de DFB foi de 0,03 ± 0,002 e de DFC foi 0,03 ± 0,006, sendo estes considerados valores baixos de NIST e que, portanto, indicam dados ideais para a predição por PICRUSt (Tabela 2). A presença de bactérias do gênero Lactobacillus pode afetar a fermentação da levedura através da produção de ácidos orgânicos e competição por nutrientes (NARENDRANATH et al, 1997;NARENDRANATH, 2003), provocando a diminuição da produção de etanol (Basso et al, 2014), a floculação das leveduras (CARVALHO-NETO et al, 2014) e a diminuição da viabilidade da levedura (THOMAS et al, 2001).…”

“…No entanto, em escala industrial, o processo fermentativo não ocorre em condições assépticas e os micro-organismos contaminantes mais importantes para o processo fermentativo da cana-de-açúcar são as Bactérias Ácido Láticas (BAL). A interação dessas bactérias com a levedura no contexto da fermentação alcoólica já foi objeto de estudo em diferentes trabalhos (BISCHOFF et al, 2008;BASSO et al, 2014). De maneira geral, a bactéria pode afetar o rendimento fermentativo da levedura pela competição de nutrientes ou pela produção de ácidos orgânicos, no entanto, aspectos mais detalhados desta interação precisam ser estudados.…”