Production of Tagatose from Galactose with CaO at Room Temperature

Abstract

This study investigates the efficacy of Sn-β zeolite, triethylamine, and CaO in the isomerization of galactose to tagatose. At temperatures over 80 °C, all three reagents exhibited low tagatose yield (< 20%). Notably, at 100 °C and a CaO/galactose molar ratio of 1/5, a galactose conversion of 64% was achieved with a tagatose selectivity of 17%. The tagatose selectivity decreased over time at this temperature. However, at room temperature, a tagatose selectivity of 56% and 73% with a CaO to galactose molar ratio of 1/1 and 2/1, respectively, was obtained with a 100% galactose conversion after 40 min of reaction. The galactose conversion had a linear relationship with the molar ratio of CaO/galactose at room temperature. This indicates that CaO functions as a stoichiometric reagent rather than a catalyst. A yellowish gel-like complex formed when the CaO/galactose molar ratios exceeded 1/2. It is noteworthy that these phenomena were not observed with MgO. In addition, low isomerization conversion from glucose to fructose was observed with CaO.