Isomerization of lactose streams catalyzed by MgO/SiO ₂

Lactulose is a synthetic prebiotic obtained from the isomerization of lactose. Industrially, lactulose is produced by either enzymatic synthesis or homogenous catalysis under strict pH control. We proposed an alternative production for lactulose directly from lactose streams using MgO/SiO2 as heterogeneous catalysis. The catalytic isomerization of lactose was performed at 110°C for 2 h over MgO/SiO2 with different MgO loads (10–40 wt.%). The formation of lactulose was evaluated in a 5% lactose solution (LA), sweet whey permeate (SWP), and acid whey permeate (AWP). Values of lactose conversion were 25–31, 55–86, and 43–58% for LAS, SWP, and AWP, respectively, regardless of the MgO load. The highest yields were achieved with SWP, reaching up to 49.38 ± 1.01%, followed by LAS (16.06 ± 1.51%) and AWP (5.26 ± 0.51%). The highest selectivity toward lactulose was obtained in SWP (75.25 ± 9.03%) 30%-MgO/SiO2. The isomerization of lactose over MgO/SiO2 showed great potential for the synthesis of lactulose from SWP directly without adjustment of the pH. Further optimization is needed to maximize the yield of lactulose at different reaction conditions.