| The cocultivation of a strain of lactic acid bacteria and a strain of yeast isolated from koumiss in Iner Mongolia,Ximeng region was studied, tentatively identified the best mixed culture fermentation conditions of the two strains:the best fermentation temperature was set at30℃for12hours and then go to37℃for the best time set at20hours in order to detect the total number of viable lactic acid bacteria during the dixenie fermentation.The optimal fermentation temperature was set at37℃for8hours and then go to30℃for the best time set at32hours fermentation in order to detect the total number of viable yeast during the dixenie fermentation, the optimal combination of the skim milk medium is formulated peptone:0.5g/100mL, sucrose:0.5g/100mL,yeast extract powder:0.5g/100mL; the selected strains of lactic acid bacteria and yeast was set as a ratio of1:1. The interactions and after-fermentation effects on the symbiosis between the lactic acid bacteria and yeast was investigated under the optimal growth conditions at the same time.Flavor metabolites formed in mixed-culture medium were determined, single culture as a control, the results are as follows:the measurement of the free amino nitrogen content showed that the ability of hydrolyzing protein of yeast is stronger than that of lactic acid bacteria; the medium is more conducive to produce more flavor compounds when mix-cultured, such as acetaldehyde, lactic acid, diacetyl, etc.; the strain of lactic acid bacteria and the strain of yeast in the fermentation process can make use of malic acid and tartaric acid as carbon source for growth. On the use of citric acid, lactic acid bacteria can metabolism citric acid, while yeast characterize in producing citric acid, suggesting the interactions between the lactic acid bacteria and yeasts;the production of formic acid, acetic acid, propionic acid in co-culture medium at different times is higher than that in single-culture medium. |
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