The isolation and characterization of yeast strains saccharomyces cerevisiae cultivated on musts of common dates: Physiological studies of the adaptation and the resistance to ethanol

Abstract

Abstract:The production of bio-alcohol from common dates need a less sensitive microorganism to the initial concentration in the ethanol, and consists on specific strains in this production. A total of 18 strains of Saccharomyces cerevisiae were isolated and identified from 18 varieties of common dates, six strains were selected, purified and tested for their abilities to perform efficient fermentation on synthetic medium. The method of selection of the most successful yeast strains that used is based on a physiological study of the adaptation and the resistance to the ethanol. The physico-chemical characterization including the moisture contents, the ash, dry matter, azote nitrogen, total sugars and acids for each variety of dates. were in the ranges of 13.04 in 15.81%; 1.78 in 2.74%; 81.64 in 86.15%; 2.25 in 2.64%; 64.0 in 78.64% and 0.23 in 1.65%, the pH varying from 5.4 to 5.95. The physiological characterization allowed selecting two from six strains of Saccharomyces cerevisiae, which possess important potentialities for production of biomass with a concentration of 18% ethanol. A better productivity of the maximal biomass of 3.58 g/l, 3.52 g/l and 3.54 g/l was obtained with 8%, 10% and 12% of ethanol for the strain S1, followed by S3 with 2.57g/l, 3.16 g/l and 3.23g/l and finally by the strain S2 with 3.43g/l, 2.66 g/l and 1.47g/l. Contrary the stains S4, S5 and S6, the quantity of biomass obtained is very low beyond 12% of ethanol. S1 and S3 are the less sensitive to the ethanol because even at 14% of ethanol, the maximal population was 1.38x10⁺⁸ UFC/ml for the strain S1 and 1.24 x10⁺⁸ UFC/ml for S3. In addition, the final population is still significant even for 16% and 18% of the ethanol. It was concluded that the strains S1 and S3 are more appropriate for the production of the bio-ethanol on a large-scale.