Study On Isolation And Identification Of Yeast And Its Producing Lactase From Natural Fermented Koumiss In Xinjiang

In this paper25strains of yeasts isolated from the natural fermented koumiss inXinjiang were identified by the method of colonial morphology, biological propertiesand5.8S rDNA sequencing. The results as follows, there are10strains ofKazachstania unispora,8strains of Kluyveromyces marxianus,4strains ofKluyveromyces lactis,1strain of Saccharomyces cerevisiae,1strains of Geotrichumcandidum. Strain27might be a new species. The identification results were importantfor us to understand and use traditional fermented dairy products of yeast resources.K.lactis and K.marxianus are capable of producing β-galactosidase was screenedfrom six strains, using X-gal as indicator, they were named as K.lactis-ZJ14,K.marxianus-ZJ19. After rescreening K.lactis-ZJ14showed good producingβ-galactosidase performance. In order to improve the K.lactis-ZJ14’s β-galactosidaseproduction performance, culture condition about the K.lactis-ZJ14by the method ofsingle factor tests, The optimum condition was as follows: temperature30℃, initialpH7.0, quantity of inoculation4%, time of culture18h. In order to raise enzymeproduction of K.lactis-ZJ14, optimize the fermentation medium, design the singlefactor tests, Plackett-Burman tests and Box-Behnken tests, the results of the optimumcomponents of zymolytic medium are as follows: lactose15.74g/L, yeast extract10.31g/L, MgSO44.84g/L, KH2PO45.42g/L. After the optimization, the yield ofβ-galactosidase was56.76U/mL.In order to better use and preservation the lactase, design tests study thecharacteristies of enzyme. The results are as follows: this enzyme has a perfectstability in the condition of4℃, the residual enzyme activity can reach up to80%kept in4℃for30d; the optimum temperature of the β-galactosidase is35℃; higherenzyme aetivity in the scope of35℃to45℃; it has a good temperature tolerancebetween20℃to55℃,the residual enzyme activity can reach up to90%kept in theseope of20℃to45℃for2h, the lactase kept in55℃for2h the residual enzymeactivity is71%; the optimum pH of the lactase is7.0with a wide range of operativepH, it has a higher enzyme activity in the pH value6.0~8.0, it has a good pH tolerance,the relative enzyme activity are all above70%after being kept2h in the condition ofpH6.0~8.0.