The isomerization kinetics of lactose to lactulose in the presence of sodium hydroxide at constant and variable pH

Lactulose (4-O-β-d-galactopyranosyl-d-fructose) is a synthetic disaccharide. Unique characteristics of lactulose have resulted in its wide use in pharmaceutical and food industries. It is produced by isomerization of lactose in an alkaline medium. The purpose of this work is to investigate the kinetics of lactose to lactulose isomerization in the presence of sodium hydroxide in constant and variable pH condition. The experiments were carried out at three temperatures (50, 60 and 70 °C) and three pH values (10, 10.5 and 11). The effect of different parameters such as temperature, pH and time on the reaction rate, conversion, sugar concentration and maximum conversion of lactose to lactulose were investigated. The experimental results were then used to calculate the rate constants and activation energies. The effects of temperature and pH on rate constants were also investigated. Finally the experimental data were compared to kinetic model predictions.