Production and characterization of a thermostable b-galactosidase from Bacillus coagulans RCS3

A strain of Bacillus coagulans RCS3 isolated from ahot-water spring produced significant b-galactosidase activity at 10 days of growth in a flask. While enzyme production was maximum at 50 °C, the highest activity was at 65 °C, where the half-life was 2 h. A 2 °C decrease in temperature increased the half-life to 15 h without significantly changing the activity, suggesting that 63 °C is the temperature of preference compared with 65 °C for a combination of good activity and stability. The b-galactosidase was also stable over pH 5-8, with peak activity at pH 6-7. It was strongly and competitively inhibited by the hydrolysis product galactose. Bivalent cations (Cu2+, Ni2+ and Hg2+) in the concentration range of 0.5-2.0 mM also inhibited enzyme activity. Both lactose solution and whey could be hydrolysed substantially within 36 h at 50 °C. The thermostability and pH-stability and good hydrolytic capability make this enzyme potentially useful in the dairy industry.