Abstract
The ability of yeasts to survive and produce significant ethanol in high sugar medium and high ethanol environment is essential for the use of such yeasts in industrial and edible ethanol production. Four Saccharomyces spp. strains () isolated from palm wine and an industrial strain were studied in high glucose medium for ethanol production and ability to survive in high sugar medium. Saccharomyces cerevisiae produced remarkable cell concentration relative to other isolates and the industrial strain, IR-2 in 16, 24 and 36% (w/v glucose) fermentation broth. S. cerevisiae survived well with good biomass yields of 2.21 and 6.74 fold in 24 and 36% w/v glucose broth, respectively. Ethanol fermentation at glucose concentration of 40% (w/v) produced 42.45 g ethanol concentration (P), 0.387g L-1h-1 volumetric productivity (Qp) and a yield (Yps) of 0.329 gg-1. The sugar tolerance property was observed in a fermentation broth with an initial pH of 5.8. Additionally, S. cerevisiae strain was adaptive to 10% ethanol in 24% glucose solution. The yield obtained and properties exhibited by this isolate compares outstandingly with published data for a range of industrially important isolates; thus, this isolate could be used to produce bioethanol in industrially sustainable processes. Key words: Saccharomyces, bioethanol, osmotic stress, ethanol tolerance, sugar tolerance, indigenous yeast.
Highlights
Ethyl alcohol is a primary metabolite of yeast produced by fermentation of sugar
The aim of the present study was to evaluate the sugar tolerance performance of yeast strain (Saccharomyces genus) found in palm wine collected from Nsukka area of Enugu State, Nigeria and to evaluate the suitability of these yeast strains in ethanol production at elevated glucose concentration
In the screening of 28 yeast isolates and a type strain (S. cerevisiae IR-2) for fermentative ability, 21 isolates were observed to be capable of gas production, while 7 isolates produced no gas in Durham’s tube (Table 1)
Summary
Ethyl alcohol (ethanol, bio-ethanol) is a primary metabolite of yeast produced by fermentation of sugar. Yeast is a small-cell fungus that ferments sugars and reproduced. The ability of yeast to thrive (ferment) in high sugar medium is one among other attributes required to qualify it for use in industrial ethanol production (Ogbonna, 2013). Fermentation of high sugar substrate offers economic advantage in the production cost and yield that will be beneficial to the energy balance (Sanchez and Cardona, 2008; Puligundla et al, 2011). The theoretical ethanol yield is 0.51 g in every 1 g of glucose (Bai et al, 2008). The higher the sugar concentration, the higher the ethanol yields
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