A Novel β-Galactosidase from Kluyvera intermedia and its Potential for Hydrolyzing Lactose in Milk

A new β-galactosidase (EC 3.2.1.23) discovered in Kluyvera intermedia (β-gal-Kli) was recombinantly produced in Escherichia coli BL21 (DE3). The bioreactor cultivation resulted in a maximum β-gal-Kli activity of 124.6 ± 25.5 μkat_{oNPGal,37 °C}/L_culture. The β-gal-Kli was purified 4.5fold to a specific activity of 172.3 μkat_{oNPGal,37 °C}/g_protein. The β-gal-Kli showed maximum activity at pH 6.5 and 50°C and was sufficiently active and stable at an industrially relevant temperature of 8°C (half-life of 63 days). The β-gal-Kli was compared to a commercially available β-galactosidase (opti-lactase LX2) for lactose hydrolysis in milk (45.3 ± 0.9 g_lactose/L) at 8°C. With the activity of 2.7 nkat_lactose/mL_milk, “lactose-free” (lactose <0.1 g/L) was realized by β-gal-Kli after 72 h, while 192 h was needed for opti-lactase LX2. Additionally, the galactooligosaccharide synthesis was observed with both these two enzymes. In conclusion, the β-gal-Kli showed its potential for the production of “lactose-free” dairy products.