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.