Isomerization and epimerization of galactose using an anion exchange resin

To produce rare sugars, such as tagatose and talose, the isomerization and epimerization of galactose were carried out in a batch system using two types of anion exchange resins. The reaction performance was investigated by applying a kinetic analysis to the reaction processes. A macroporous-type anion exchange resin generated higher reactivity than a gel-type resin. It was found that there were optimal yields of isomerization and epimerization products that were dependent on the reaction temperature, resin quantity, and substrate concentration. The maximum yields of tagatose (17.6 %) and talose (17.1 %) were obtained at 50°C and the initial concentration of 10 % (w/v) galactose with 0.50 g of the macroporous-type anion exchange resin and 2.5 mL of water. The kinetic analysis revealed that the equilibrium constants for the isomerization of galactose to tagatose and the epimerization of galactose to talose were estimated to be 0.25 and 0.22, respectively. The constant for the epimerization of tagatose to sorbose was 0.19. Consequently, the equilibrium yields of tagatose, talose, and sorbose were estimated to be 17 %, 15 %, and 3 %, respectively. Moreover, the decomposition of substrate and products by high alkali conditions was indicated, and holding the appropriate alkali condition led to efficient production of rare sugars.