Improvement in the Anti-staling Capability of Beer by Genetically Modifying Industrial Brewing Yeast with High Glutathione Content

On the basis of homologous recombination, recombinant plasmid pRKG was constructed by replacing the internal fragment of 18S rDNA of pRJ-5 with a copy of γ-glutamylcysteine synthetase gene (GSH1) from the industrial brewing yeast strain G03 and a copy of G418 resistance gene (Kan) as the dominant selection marker. The fragment 18S rDNA::(Kan-GSH1) obtained through the PCR reaction was integrated to the chromosomal DNA of G03 strain, and the recombinants were screened by G418 resistance. It was shown that the GSH content of beer fermented with the recombinant strain SG1 was 16.6% higher than that of G03, and no significant difference in routine fermentation parameters was found. To test the genetic stability, strains SG1 was inoculated into flasks and continuously transferred five times. The intracellular glutathione content of strain was basically kept as a constant. It is an instructive attempt of genetically modifying industrial brewing yeast, as GSH1 was obtained from the host itself.