Studies On Selection Of Yeast With High Vitalistic Lactase And Properties Of The β-Galactosidase

In This paper .thirty strains of yeast were isolated from nineteen samples of fermented milk(10 koumiss samples.three fermented goat milk samples.four fermented milk samples,two shubat samples) that were collected from the west-centre region of Inner Mongolia from which we aimed to select the yeast with high vitalistic b-Galactosidase .According to the results of dedermination that were the metabolism rate and ratio vitality of b-Galactosidase.STK-1-1 has been selected .The result of identification showed that STK-1-1 belonged to Kluyveromyces marxianus of Kluyveromyces.In the research,fermenting properties of STK-1-1, biological properties of b-Galactosidase and the optimization of producting technology of low-lactose-milk have also been studied.The results showed that the logarithmic growth phase of STK-1-1 is 18-30h,suitable temperature range 25-30 C reasonable inoculating content 6%.Under this condition,a large number of higher vitality of yeast cells could been achieved; B-Galactosidase of STK-1-1 is neutral,suitable pH=6.5, suitable temperature range 35-45 C,Within six ions, Cu2+,Fe2+,Ca2+ can inhibit the vitality of P -Galactosidase while K, Na+, Mg2+, can promote the vitality of P-Galactosidase. Therein, vitality of b-Galactosidase can increase 18.4% by Mg+2, Using the P-Galactosidase producting low-lactose-milk, the optimum producting technology are the density of b-Galactosidase 1.5%,the temperature of heat preservation 37 C,the time of heat preservation 3h.Under this condition,the lactose of milk have been decreased from 4.64% to 2.2%.The result of the qulity index of sensory orgar showed that except the colour index,flavour,sweet and taste of low-lactose-milk are all superior to general milk.