Formation and degradation of individual GOS formed by B. breve β-gal I (A) and β-gal II (B) during lactose conversion.

Reaction conditions: initial lactose concentration of 200 g L⁻¹ in 50 mM sodium phosphate buffer (pH 6.5) with 1 mM Mg²⁺ and 30°C and 1.0 U_Lac mL⁻¹ β-gal I or 2.5 U_Lac mL⁻¹ β-gal II. Symbols: (•) D-Galp-(1→6)-D-Glc; (▪) D-Galp-(1→6)-D-Gal; (▴) Galp-(1→3)-D-Gal; (Δ) D-Galp-(1→3)-D-Glc; (□) D-Galp-(1→3)-D-Lac; (○) D-Galp-(1→4)-Lac, (+) D-Galp-(1→6)-D-Lac.