Breeding Of High-quality Saccharomyces Cerevisiae And Development Of Direct-acting Fermentation Starter

Yeast is a unicellular fungal organism,which contains many high-quality yeast protein,B vitamins,nucleic acids,minerals and some active health care substances.Yeast has high nutritional value,simple cultivation and rapid growth and reproduction.Due to the high nutritional value of yeast,simple culture and rapid growth,yeasts are widely used in modern food and modern biology research.In order to dynamically understand the changes in the variables during the fermentation process and analyze the metabolic activities,such as bacterial reproduction status,substrate consumption,the rate of product production,high-quality yeasts are separated,screened and measured their growth characteristics,fermentation characteristics and parameters of fermentation broths at different stages,such as bacterial density,lactic acid,and solids content,which could contributed to grasp the characteristic parameters of high-quality brewing strains to provide data basis for controlling and optimizing production conditions in production.At the same time,the combination of high-quality strain freeze-dried bacterium powder technology is researched,which is suitable for certain special fermentation substrates to make up for the shortcomings of the strains in the current yeast market that are not strong enough to make industrial fermentation faster,more rational and specific.In this experiment,yeast strains were separated and screened from berries and orchard soils in Inner Mongolia area.The yeast strains with sugar-tolerant,ester-producing and high-fermentation characteristics were selected for transformation and screening.The biological characteristics and fermentation characteristics of the yeast strains after transformation were studied.The sugar-tolerance mechanism of sugar-tolerant yeasts was studied and the processing technology of direct-acting starter was studied too.The main results are as follows:1.The 200 strains of yeast were screened from soils and berries.The majority of yeast colony were round and white or milky white opaque,the surface was convex,smooth and delicate,with neat edges.it was viscous and prone to pick up,the color texture was relatively uniform;Individual colonies had smooth surfaces,rough folds,and uneven color texture.After picking up colonies and safranin staining,it was observed by microscopy that the cells were spherical or ellipsoidal,with budding or split reproductive phenomena,all with typical yeast morphology characteristics.2.The 200 strains of yeast strains had been screened by one,two,three stage screening,5 strains of sugar tolerance yeast were selected,5 strains of yeast produced ester were selected,and 5 strains of high fermentative yeasts were selected.Then using CXJ-1,CX1,K2"-2 and K3-2 as the starting strain for UV-induced mutation,4 dominant yeast,CXJ-11,CX13,K2"-27,and K3-23 were obtained.And K2"-27 was identified as Kazachstania unispora,and the other three strains were Saccharomyces cerevisiae.?1?The sugar tolerant yeast CXJ-11 and CX13 could enter logarithmic phase after3h.The maximum tolerable concentration of strain CX-11 to alcohol,pH,SO₂ and sugar was 10%vol,2.0,600mg/L and 65%,respectively.And for strain CX13 was 16%vol,1.5,600mg/L,65%.?2?The maximum ester yield of K2"-27 was 2.74±0.19g/L,which could enter logarithmic phase after 4h.The maximum tolerable concentration of strain K2"-27 to alcohol,pH,SO₂ and sugar was 10%vol,2.0,600mg/L and 60%.?3?The highest CO₂ weight loss of yeast K3-23 was 9.68±0.49g,which could enter logarithmic phase after 3h.The maximum tolerable concentration of strain K2"-27 to alcohol,pH,SO2 and sugar was 12%vol,2.0,600mg/L and 60%.?4?In the simulated grape juice fermentation test,the fermentation degree of CXJ-11,CX13,K2"-27 and K3-23 was all above 70%,and the soluble solids were all below 5.0,and the alcoholicity was above 8.0%vol.Among them,the alcoholicity of CXJ-11 and CX13 was 8.5%vol.All the mutant strains were superior to the industrial strain CK?Saccharomyces cerevisiae?.3.The mechanism of sugar tolerance of CXJ-11 and CX13 was studied.It was found that under high glucose stress,the dry weight,intracellular trehalose,glycerol content and cell membrane permeability of the yeast strain were significantly changed,and the dry weight was decreased under high glucose stress.At the same time,Glycerol and trehalose increased,but the permeability decreased.On the contrary,there was less effect on the solid content,reducing sugar,ethanol content,mitochondrial membrane potential changes and cell membrane integrity.The conclusion was that high glucose stimulation had less damage to the membrane and membrane potential,and had a greater impact on ion transport.4.The process of compound direct-acting fermentative agent suitable for ice wine production was studied to determine the optimal process for the production of freeze-dried bacterial powder:both sugar-tolerant yeast CX13 and ester-producing yeast K2"-27 were 3%,freeze-dried trehalose,sucrose,glycerol and sodium glutamate was 7%,7%,4%,and 2%,respectively.Four kinds of protective agents were mixed and suspended in 5%skim milk as the final lyophilized protection solution,the lyophilized protection solution and the complex bacteria were mixed in a ratio of 2:1 to freeze-dry.The maximum survival rate of microbs was 85.33%.