Time course of GOS formation (A) and formation and degradation of GOS during lactose conversion (B) catalyzed by B. breve β-gal I (•) and β-gal II (○).

The reaction was performed at 30°C at an initial lactose concentration of 200 g L⁻¹ in sodium phosphate buffer (pH 6.5) and 1 mM MgCl₂ using 1.5 U_Lac mL⁻¹_. Values are the mean of two independent experiments and the standard deviation was always less than 5%.