The acid tolerant and cold-active β-galactosidase from Lactococcus lactis strain is an attractive biocatalyst for lactose hydrolysis

The gene encoding the β -galactosidase from the dairy Lactococcus lactis IL1403 strain was cloned, sequenced and overexpressed in Escherichia coli . The purified enzyme has a tetrameric arrangement composed of four identical 120 kDa subunits. Biochemical characterization showed that it is optimally active within a wide range of temperatures from 15 to 55 °C and of pH from 6.0 to 7.5. For its maximal activity this enzyme requires only 0.8 mM Fe 2+ and 1.6 mM Mg 2+ . Purified protein displayed a high catalytic efficiency of 102 s −1 mM −1 for lactose. The enzyme stability was increased by immobilization mainly at low pH (from 4.0 to 5.5) and high temperatures (55 and 60 °C). The bioconversion of lactose using the L. lactis β -galactosidase allows the production of lactose with a high bioconversion rate (98 %) within a wide range of pH and temperature.