Kinetic Analysis of Lactulose Production from Lactose in Subcritical Aqueous Ethanol

Abstract

Production of lactulose from lactose in subcritical aqueous ethanol was analyzed through a series of kinetic experiments. Assuming first-order reaction kinetics for both the reversible isomerization between lactose and lactulose and the hydrolysis of these disaccharides, the rate constants for these processes were estimated from our previous results (Soisangwan et al., in press) using the concentration-time integrals method. In subcritical water, the rate constants for the hydrolysis of lactose and lactulose to their constituent monosaccharides were found to be greater than the rate constant for the isomerization of lactose to lactulose. In subcritical aqueous ethanol, on the other hand, the rate constant for this isomerization reaction was found to be greater than the rate constants for both of the hydrolysis processes. The activation energies for the isomerization of lactose to lactulose and its reverse reaction were determined as 105 and 153 kJ/mol, respectively.