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The need to freeze dough is increasing in bakery production. Frozen dough can be stored for a long time without quality change. The capacity of bakery production can be increased in this way, and in the same time, the night shifts can be decreased. Yeast cells can be damaged by freezing process resulting in poor technological quality of dough after defrostation (longer fermentation of dough). The influence of frozen storage time of dough on survival percentage of Saccharomyces cerevisiae was investigated. Dough samples were taken after 1, 7, 14 and 28 days of frozen storage at -20°C. After defrosting, at room temperature, samples were taken from the surface and the middle part of dough (under aseptic conditions), and the percentage of living S. cerevisiae cells was determined. During frozen storage of dough, the number of living S. cerevisiae decreased. After 28 days of frozen storage, the percentage of live cells on the surface and inside the dough was 53,1% and 54,95%, respectively. The addition of k-carragenan to dough increased the percentage of living cells in the middle part of dough up to 64,63%. Pure cultures, isolated from survived S. cerevisia cells in frozen dough by agar plates method (Koch's method), were multiplied in optimal liquid medium for yeasts. The content of cytochromes in S. cerevisiae cells was determined by spectrophotometric method. The obtained results showed that the content of cytochromes in survived S. cerevisiae cells was not affected by dough freezing process. Growth rate and fermentative activity (Einchor's method) were determined in multiplied cells.

Response surface methodology (RSM) was used for selecting optimal fermentation time and initial sugar mass fraction in cultivation media based on raw juice from sugar beet in order to produce ethanol. Optimal fermentation time and initial sugar mass fraction for ethanol production in batch fermentation by free Saccharomyces cerevisiae cells under anaerobic conditions at the temperature of 30 °C and agitation rate of 200 rpm were estimated to be 38 h and 12.30 % by mass, respectively. For selecting optimal conditions for industrial application, further techno-economic analysis should be performed by using the obtained mathematical representation of the process (second degree polynomial model). The overall fermentation productivity of five different types of yeast was examined and there is no significant statistical difference between them. [ABSTRACT FROM AUTHOR]

The use of biofuels as an alternative to fossil fuels has expanded in the last few decades. The aim of this study was to examine the application of different strains and forms of Saccharomyces cerevisiae for raw, thin and thick juice fermentation in order to produce bioethanol. According to the obtained results the strain applied in the form of pressed blocks with 70 % w/w moisture, attained higher value of the specific growth rate and lower value of ethanol yield in comparison with strains applied in dried form. In all culture media attained efficiency of sugar utilization was at least from 98-99 % w/w. Maximum productivity was achieved around 30th hour of fermentation and amounted ≈1.8 g l-1 h-1 for all applied yeast strains. Therefore, optimal duration of the process in technical and economic terms should be considered. [ABSTRACT FROM AUTHOR]