Screening and isolation of baker yeast mutants with freezing and high osmotic pressure resistance and more gas generation ability

The baker yeast Saccharomyces cerevisiae is known as the major microorganism in the bread-making process and its applications worldwide. Therefore, lots of efforts have been made to develop the properties of its strains, like creating strains resistant to stresses such as; air-drying, freezing, high temperature, high osmotic pressure, andhigh-sucrose concentrations. The aim of this study was screening and isolation of baker yeast mutants resistant to freezing and high osmotic pressure with high gas generation ability. For this reason, the random mutagenesis by UV radiation process was done in different time cycles in order to find the time point when there are 40% viable cells for each strain. Mutagenesis at that point was repeated and 17 mutants of three baker yeast strains of Y1, Y3 and H were screened and isolated after culturing on YPDA media with high NaCl and Sucrose concentrations. The amount of CO2 gas generated by the resultant mutants was measured by a gas-measuring device and 10 mutants with gas generation ability were isolated. Consequently, two more efficient isolated mutants of each strain were analyzed by freezing tests at -20°C, thus the ones with higher viability in comparison to their wild types were chosen. Eventually, 3 mutants, Y1M1, Y3M1, and HM2, with the highest resistance to freezing and high osmotic pressure stress with high gas generation ability were screened and isolated.

Keywords:

Baker yeast , Screening , Isolation , Random mutagenesis , Gas generation