Production, Purification, and Characterization of a Potential Thermostable Galactosidase for Milk Lactose Hydrolysis from Bacillus stearothermophilus

Sodium dodecyl sulfate-PAGE analysis of the purified thermostable β-galactosidase from different stages. M = protein marker; lane 1 = cell-free extract; lane 2 = fraction of heat treatment; lane 3 = fraction of (NH₄)₂SO₄ precipitation; lane 4 = fraction of ÄKTA DEAE column; lane 5 = fraction of ÄKTA Sephacryl S-100 column.

Effect of pH on activity of the recombinant β-galactosi-dase. Error bars represent the standard deviation from 3 separate experiments.

Effect of temperature on activity of the recombinant β-galactosidase. Error bars represent the standard deviation from 3 separate experiments.

The thermostability of β-galactosidase from Bacillus subtilis WB600/pMA5-bgaB at different temperatures: ■ = 60°C; • = 65°C; ▴ = 70°C. Error bars represent the standard deviation from 3 separate experiments.

Lineweaver-Burk plot of the thermostable β-galactosidase.

Effect of substrate-like inhibitors on the activity of thermostable β-galactosidase: ■ = control; ▴ = lactose (10mM); • = galactose (100mM); ♦= melibiose (100mM); ♦= melitriose (100mM).

Hydrolysis of lactose in milk by thermostable β-galactos-idase: ■ = 55°C, 1 U/mL; • = 55°C, 2 U/mL; ▴ = 60°C, 1 U/mL; ♦ = 65°C, 1 U/mL; ♦ = 65°C, 2 U/mL. Error bars represent the standard deviation from 3 separate experiments.