Abstract
Spent Sulfite Liquor (SSL) from wood pulping facilities is a sugar rich effluent that can be used as feedstock for ethanol production. However, depending on the pulping process conditions, the release of monosaccharides also generates a range of compounds that negatively affect microbial fermentation. In the present study, we investigated whether endogenous yeasts in SSL-based ethanol plant could represent a source of Saccharomyces cerevisiae strains with a naturally acquired tolerance towards this inhibitory environment. Two isolation processes were performed, before and after the re-inoculation of the plant with a commercial baker’s yeast strain. The isolates were clustered by DNA fingerprinting and a recurrent Saccharomyces cerevisiae strain, different from the inoculated commercial baker’s yeast strain, was isolated. The strain, named TMB3720, flocculated heavily and presented high furaldehyde reductase activity. During fermentation of undiluted SSL, TMB3720 displayed a 4-fold higher ethanol production rate and 1.8-fold higher ethanol yield as compared to the commercial baker’s yeast. Another non-Saccharomyces cerevisiae species, identified as the pentose utilizing Pichia galeiformis, was also recovered in the last tanks of the process where the hexose to pentose sugar ratio and the inhibitory pressure are expected to be the lowest.
Highlights
Lignocellulosic biomass, composed of cellulose, hemicellulose and lignin, represents a potential source of fermentable sugars for the production of fuels and bulk chemicals (Wyman and Goodman 1993; Hahn-Hägerdal et al 2006)
We report on the isolation and identification of a resident yeast species in a Spent Sulfite Liquor (SSL) ethanol plant that operates in multistage continuous mode with yeast cell recirculation using a mixture of spruce (Picea abis) and pine (Pinus sylvestris) hydrolysate
Aerobic cultivation on solid rich medium was chosen in order to select S. cerevisiae strains as well as any other type of yeast contaminants
Summary
Lignocellulosic biomass, composed of cellulose, hemicellulose and lignin, represents a potential source of fermentable sugars for the production of fuels and bulk chemicals (Wyman and Goodman 1993; Hahn-Hägerdal et al 2006). In pulp and paper mills, the cellulose fraction can be used for the production of pulp, paper, board and cellulose-based products. This requires treating wood biomass with a cooking liquor to obtain the discrete fibres. Several phenolic compounds, such as vanillin, guaiacol and coniferyl aldehyde, can be present in lignocellulose hydrolysates as a result of lignin degradation All these compounds have the ability, at different levels, to inhibit microbial activity during ethanol fermentation, thereby resulting in increased lag phase, reduced ethanol production rate and/or reduced final ethanol yield (Boyer et al 1992; Navarro 1994; Larsson et al 1999a; Almeida et al 2007)
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