Obtaining yeast cultures for alcoholic fermentation from lyophilized strains Saccharomyces.

NIKOLOVA , R., Tsv. TSVETKOV and T. DONEV, 2008. Obtaining yeast cultures for alcoholic fermentation from lyophilized strains Saccharomyces. Bulg. J. Agric. Sci., 14: 16-21 The objective of the present study is to obtain yeast cultures for alcoholic fermentation from lyophilized strains Saccharomyces with high number of viable cells. Two types of strains of brewer’s yeasts – the strain Saccaharomyces uvarium carlbergensis No 569 and the strain Saccharomyces cerevisiae No 576 are used, which are included in the Catalogue for National Bank for Industrial Microorganisms and Cell Cultures. According to their certificate, they are used for fermentation of sugars of the wheat grain and as a result ethyl alcohol up to 8 g.kg-1 is obtained. Two methods have been applied for yeasts cultivation during the process of obtaining yeast cultures: deep cultivation in a liquid medium and surface cultivation on agar medium. As a result of many experiments for cultivation of yeast strains, it was determined the highest growth for colonies can be achieved on Saburo medium with 4 g.kg -1 dextrose at 30 o C, pH 6.0 – 6.2 and time of cultivation time 72 hours. In the laboratory cultures, obtained from both tested strains, we found high number of viable yeast cells and the values obtained in strain No 576 were 108 colony-forming (CFU) units/cm3.The culture obtained was an industrial monoculture, containing 9,66. 108 CFU/cm3 living yeast cells of strain 576 which exceeded the results obtained by other scientists. This method is considered as a new one for the practice and may provide intensive process for alcoholic fermentation. We investigated the factors having influence on the growth and development of the yeasts cells during the process of obtaining yeast cultures and their parameters for optimizing the fermentation process. The results obtained can serve as a proof for fermentation and reproductive activity of the selected strains of brewer’s yeasts. In that way, the wheat grain may be used as a valuable source for the production of bioethanol through alcoholic fermentation.