Improvement Of Brewing Yeast Flocculation Ability Of Genetically Construction In Flo8 Mutant

Brewing yeast is the soul of beer production which plays a key role through the whole brewing process. Flocculation is described as a phenomenon that yeast getting together and quick sedimentation from the medium. The flocculation of brewing yeast gets great attention because of its significant in practice production. Nicer flocculation characteristic could not only save the energy, but also avoid the yeast autolysis. Premature yeast flocculation (PYF) is an abnormal phenomenon causing harm for brewing production which needs to be avoided.A primary aim of this research was to knockout of flo8 gene in industrial brewing yeast G-03 by PCR-mediated gene disruption. We obtained a transformant G-03/f8 based on the homologous recombination with KanMX gene. The PCR analysis showed that flo8 gene in the G-03/f8 was deleted, and the stability of the transformant was verified to be good. We compared the physiological performance and fermentation performance of G-03/f8 and G-03 during flask fermentation. We care most on the fermentation performance when using the malt with high PYF value.Compared with the host strain G-03, G-03/f8 could reach the same level in growth and fermentation routine parameters during flask fermentation. When using high PYF(premature yeast flocculation) value malt in brewing, the ethanol and fermentation degree of G-03/f8 decreased insignificantly, which is better than G-03 in the fermentation routine parameters. The G-03/f8 is insensitive to high PYF value wort, which insured the applying on it.In practical production, the glucose, maltose, Ca2+ concentration, pH value, temperature and ethanol are important parameters in wort which could be controlled. We changed these factors and we studied the changes of the flocculation characteristic caused by these factors. The result showed that the flocculation characteristic of G-03/f8 is weaken because of the knockout of flo8 gene in all the cases. When the sugar or Ca2+ concentration increased, the flocculation characteristic increased. The flocculation characteristic of yeast was strongest when the pH value was between 4.0 and 5.0. The change of flocculation characteristic did not range in low temperature. The increase of ethanol concentration weakened the flocculation characteristic.