Breeding Of Brewing Yeast With Lower-level Proteinase A And Application In Pilot Scale Fermentation

The stability of draft beer foam is a critical character that reflects beer quality. Although there are many factors that positively and negatively influence foam stability, the most important negative factor is proteinase A. Brewing yeast excretes proteinase A into the wort during fementation. Proteinase A diminishes the hydrophobicity of foam-positive polypeptides and reduces beer foam stability. The study mainly focuses on breeding of brewing yeast of the low ability to excrete proteinase A during wort fementation.Many mutagenesis methods, including He-Ne laser physics mutagenesis, and nitrite, NTG, EMS chemical mutagenesis, were used and the optimal experiment conditions were studied. The mutation effects of continuous used NTG and EMS was the best among these mutagens. Then the combination NTG and EMS were used and obtained a strain—GM235 with good fermentation performance and low protease A lever. GM235 was applied to scaling-up fermentation.The scaling-up fermentation showed that the fermentation performance and flavor of mutant GM235 were better than original strain, and proteinase vitality reduced by 19.31%, under conditions of 100L fermentor for 9 days. Both the ability of decline of sugar concentration and reducing power of diacetyl were slightly stronger. N-propyl alcohol was slightly higher, while isobutanol, isoamyl alcohol, active amyl alcohol and acetidinthe were all lower. Beer foam from mutant GM235 fermentation was more delicate and lasted longer than original strain. The mutant GM235 is a strain with good application prospect in the beer brewing.