Compound Mutagenesis Aspergillus Candidus On Screen Of Lactase-high-yield Strain

According to estimate,70% people all over the world have lactose cacochylia or the phenomenon of lactose intolerance. The lactase can hydrolyze to glucose and the galactose with lactose in milk. Using of lactase to produce low-lactose dairy products provides a feasible method for lightening symptoms of lactose digestion. So we make the following methods:use o.lmol/L nitrite to treat the Aspergillus candidus, and then Irradiate the culture plate with 15 watt ultraviolet lamp at vertical distance 15cm. We can get mutant strain through prescreening and positive mutant through flask fermentation, and then we can gain crude extract from centrifugation. What's more, we measure lactase activity, study the nature of the lactase enzyme and concentrate the crude enzyme with ultra filtration apparatus. Through the experiment, we determine the best combination:treat 11min on the Aspergillus spore with nitrite and UV 5 min. The result is that the lactase activity increases to 1.1 U/g from 0.13U/g. wo also find that the suitable temperature is 55℃, the most suitable pH is 5.0 and Cu2+ has obvious inhibitory action on the activity of the enzyme, Mg2+ has obvious promoting effect, the other ions have little effect on it under low concentration. The ultra filtration membrane successfully concentrates the enzyme solution and the enzyme Concentration increased 19-fold.We get a high-yield mutant with production increased 8.5-fold.