Isomerization and hydrolysis of lactose in arginine solution under microwave heating

Lactulose is a synthetic disaccharide used as a treatment for constipation and also shows prebiotic properties in humans. In this study, isomerization of lactose to lactulose and hydrolysis of lactose to monosaccharides in an arginine solution were investigated under microwave heating. Increasing the arginine/lactose molar ratio from 0.05 to 0.2 at an initial lactose concentration of 0.2 M resulted in the highest lactulose yield (21.7 %) and monosaccharide yield of 4.9 % after 90 s of heating at 640 W. Varying the initial lactose concentration from 0.1 to 0.4 M did not affect the yield, though productivity increased significantly. The highest lactulose productivity (1369 g/(L·h)) was achieved by heating a 0.4 M lactose solution with an arginine/lactose molar ratio of 0.2 at 800 W for 60 s. Additionally, it was found that using high microwave energy with shorter heating duration (800 W for 60 s) helped suppress browning reactions.