Effects of lactobacilli on yeast-catalyzed ethanol fermentations

Abstract

Normal-gravity (22 to 24°Plato) wheat mashes were inoculated with five industrially important strains of lactobacilli at ϳ10 5 , ϳ10 6 , ϳ10 7 , ϳ10 8 , and ϳ10 9 CFU/ml in order to study the effects of the lactobacilli on yeast growth and ethanol productivity. Lactobacillus plantarum, Lactobacillus paracasei, Lactobacillus #3, Lactobacillus rhamnosus, and Lactobacillus fermentum were used. Controls with yeast cells but no bacterial inoculation and additional treatments with bacteria alone inoculated at ϳ10 7 CFU/ml of mash were included. Decreased ethanol yields were due to the diversion of carbohydrates for bacterial growth and the production of lactic acid. As higher numbers of the bacteria were produced (depending on the strain), 1 to 1.5% (wt/vol) lactic acid resulted in the case of homofermentative organisms. L. fermentum, a heterofermentative organism, produced only 0.5% (wt/vol) lactic acid. When L. plantarum, L. rhamnosus, and L. fermentum were inoculated at ϳ10 6 CFU/ml, an approximately 2% decrease in the final ethanol concentration was observed. Smaller initial numbers (only 10 5 CFU/ml) of L. paracasei or Lactobacillus #3 were sufficient to cause more than 2% decreases in the final ethanol concentrations measured compared to the control. Such effects after an inoculation of only 10 5 CFU/ml may have been due to the higher tolerance to ethanol of the latter two bacteria, to the more rapid adaptation (shorter lag phase) of these two industrial organisms to fermentation conditions, and/or to their more rapid growth and metabolism. When up to 10 9 CFU of bacteria/ml was present in mash, approximately 3.8 to 7.6% reductions in ethanol concentration occurred depending on the strain. Production of lactic acid and a suspected competition with yeast cells for essential growth factors in the fermenting medium were the major reasons for reductions in yeast growth and final ethanol yield when lactic acid bacteria were present.

Microbial contamination of fuel ethanol fermentations

“…The effects of lactobacilli contamination have been extensively studied in the laboratory. It has been generally believed that lactobacilli cause inhibition of Saccharomyces or limit ethanol production through two basic methods; either production of lactic and acetic acids or through competition for nutrients (Narendranath et al 1997;Narendranath 2003). However, a number of researchers have demonstrated that these mechanisms may not completely account for this inhibition.…”

“…While it is true that acetic acid formation is associated with aerobic growth of D. bruxellensis (Narendranath et al 1997;Abbott and Ingledew 2005;Blomqvist et al 2010), there is not enough produced to completely explain the drop in ethanol production (Abbott and Ingledew 2005). Additionally, D. bruxellensis grows more slowly and therefore does not present itself as a contaminant until later in the fermentation (Abbott and Ingledew 2005).…”

Characterization, phylogenetic affiliation and probiotic properties of high cell density Lactobacillus strains recovered from silage

“…4 The abundance of LAB strains in silages depends on several factors, including preparation conditions, time of harvesting and duration of silage preparations. 14 The strains showed different biochemical characteristics relative to each specific species. On the basis of biochemical properties, L. plantarum strains could be divided into two groups: nine L. plantarum strains grew in D-arabinose but did not grow in the presence of D-arabinose; in contrast, none of the L. plantarum strains grew on L-arabinose.…”

Nisin incorporation enhances the inactivation of lactic acid bacteria during the acid wash step of bioethanol production from sugarcane juice

“…LF, a heterofermentative organism, is the most predominant contaminant in industrial fermentation in Brazil (Costa et al 2015) and can cause yeast flocculation capable of decreasing the bioethanol production (Dellias et al 2018). LPC has been shown to possess the ability to produce levels of lactic acid that can result in more than 2% reduction in ethanol production even at a low level of inoculation (10 8 CFU per litre) (Narendranath et al 1997). Although there are few reports about LPP and LG contamination effects, the LPP and LG strains used in this study were isolated from sugarcane and cider respectively, and show a very strong acid resistance (Daum 2016).…”