Research On Mutation Breeding Of Osmophilic Beer Yeast And Its Fermentation Performances

Fermentation performance of four lager yeasts (Saccharomyces pastorianus FBY0095,FBY0096, FBY0097and FBY0098) with different genetic background during high gravityfermentation was investigated in the present study. Then, two yeast strains of FBY0097andFBY0098which showed better fermentation performance were chosen as the original strains.With compounded mutation of ultraviolet radiation and EMS, six variants were obtained bydomestication from each of the original strains. Finally, two variants (FBY0097.2andFBY0098.5) with the best metabolism properties and fermentation performance were selectedby employing conical flask and pilot-scale fermentation vessel fermentations. The mainresearch contents and results are as follows:(1) Fermentation performance of four lager yeasts (Saccharomyces pastorianus FBY0095,FBY0096, FBY0097and FBY0098) with different genetic background during normal(12°P) and very high gravity (24°P) fermentations was compared. The results showed thatlager yeasts FBY0097and FBY0098exhibited better fermentation performance undervery high gravity condition and therefore were chosen as original strains.(2) After compounded mutation of ultraviolet radiation and EMS,12variants with the biggestcolony were obtained by domestication and were numbered as FBY0097.1–FBY0097.6and FBY0098.1–FBY0098.6, respectively.(3) Fermentation performance of12variant strains and2original strains during very highgravity fermentation (24°P) in conical flask was compared. Results showed that thevariant strain FBY0097.2of FBY0097exhibited the best fermentation performance in the6variant strains, with18.04%fermentability increased and10.63%(v/v) ethanolincreased; the variant strain FBY0098.5of FBY0098exhibited the best fermentationperformance in the6variant strains, with3.79%fermentability increased and8.24%(v/v)ethanol increased.(4) Physiological characterization and fermentation performance of the variant strains(FBY0097.2and FBY0098.5) and the original strains (FBY0097and FBY0098) duringvery high gravity fermentation in pilot-scale fermentation vessel were further compared.Results showed that the intracellular trehalose contents of variant strains were higher thanthose of original strains. Furthermore, variant strains exhibited better fermentationperformance compared with original strains. FBY0097.2and FBY0098.5decreased the fermentation period by7.41%and8.33%and increased the ethanol yield by3.03%and4.27%, respectively.