Abstract: The extraction of the β-galactosidase produced by La-A and La-B was studied with the ultrasonic cell-break method. Meanwhile, the activity of β-galactosidase was assayed with reagent ONPG as substrate.Through the single-factor experiment and orthogonal experiment, the optimum technology was chosen. The results showed that the optimum conditions on cell-break of La-A with the ultrasonic method were: work time 7.6s,work/terral time 28s/20s, and temperature 36℃ and B was work time 6.8s, work/intermission time 20s/20s, and temperature 37℃. In these conditions, the activity of β-galactosidase produced by La-A and La-B reached 5.963μmol ONP/L·min and 6.683μmol ONP/L·min respectively. Therefore, Lactobacillus acidophilus had higher activity of producing β-galactosidase.

Key words: Lactobacillus acidophilus； &beta, -galactosidase； the ultrasonic cell-break；