Mechanism And Pure Culture Of The Starter For Milk Fermentation With Tibetan Mushroom

Tibetan Mushroom is a mixture of lactobacteria, yeast, and acetic acid bacteria.The mixture forms kernel like flower of lotus.Milk fermented with the mixture showed many biological functions including enhancing immunity system,antitumor,lowering blood pressure, and reducing blood lipid.The microorganism flora in the kernel would change with the local wheather and environment.Therefore, the product quality can not be guaranteed under the traditional production method in which the starter for fermentation was transferred unprotectedly between different persons in the form of kernel.In order to get a sTab starter to guarantee the product quality,the paper investigated the variation of numbers of main microorganism flora in the kernel,and nutrients and metabolic products in the fermented milk during fermentation.Machnism of the fermentation was explored on the basis of relationship between the number of bacteria,nutrient consumption and product production.The isolated beneficial strains and those industrialized strains were optimized to make a mixture of pure culture of starter for fermentation.The main contents and results were listed as following:1.Number of the dominating microorganisms in the kernel,and lactose,ethanol,acetic acid,lactic acid,and pH in the fermented milk were detected by intervals during the fermentation.It was found the number of yeast,lactobacteria,and acetic acid bacterial in the kernel decreased in the first few hours and then increased slowly to the end.However, except of acetic acid bacterial,yeast and lactobacteria did not show significant change in number during the fermentation.In the fermented milk,lactose content kept decrease during the fermentation but the decrease was slowed down in the later stage.Lactic acid and acetic acid kept increasing during the fermentation.The variation of the number of dominating microorganisms showed close relationship to their corresponding metabolic products.2.Antibacterial activity of the fermented milk to pathogens of Enteropathogenic E.coli, Staphylococcus aureus and Salmonella were detected by intervals during the fermentation. The fermented milk showed different antibacterial effect on the three pathogens.The milk fermented for 21 to 24h showed the highest inhibitory activity.By using pure chemical compounds in the same concentration as that in the fermented milk,lactic acid showed as the most important antibacterial compound in the fermented milk.The antibacterial activity could be enhanced when lactic acid,acetic acid,and ethanol were in low levels.However,such synergism effects of the other products on the antibacterial activity of lactic acid weaked when lactic acid,acetic acid,and ethanol were in high levels.3. Based on the isolated strains of lactobacteria X3 and yeast Y6,and industrialized strains of yeast Y7,lactobacteria Lb and St,the optimal compositiona and conditions for pure culture of starter were determined as mixed yeast(Y6:Y7=1:1) to mixed lactobacteria (X3:Lb:St=1:1:1) ratio of 1:2,inoculation quantity of the starter of 5%,and temperature for fermentation of 37oC.The milk fermented with the above optimal starter mixture showed higher antibacterial activity than that fermented only with the isolated strains or the industrialized strains.4. Protectants the pure culture of starter were optimized as a mixture of 10% skimmed milk,5% glycerol,0.5% Vc,1.5% gelatin, and 10% sucrose for lactobacteria strains X3;10% skimmed milk,5% glycerol,1% L-cysteine,10% sucrose,and 10%maltose for yeast strains Y6 and Y7.Pure culture of the lactobacteria and yeast still kept high activity for starting fermentation.By using this pure culture,the inoculation ratio could be reduced by more than 100 times compared with the fresh inocular.This met the requirement of inocular by production of fermented milk by processing of Directed Vat Set (DVS).The optimal protectant for the freeze-drying of the kernel of Tibetan Mushroom was optimized as 10% skimmed milk,5% glycerol,10% sucrose,10% maltose,0.5% Vc,1.5% gelatin and 1 %L-cysteine.However, the activity of the kernel was reduced greatly for starting the fermentation.