Simultaneous production of d-allulose and d-tagatose from lactose

The high-demand rare sugars d-tagatose and d-allulose may be produced from lactose in a combined process, though this dual conversion has not yet been demonstrated. Four enzymes from thermophilic organisms were cloned and expressed in Escherichia coli to synthesize d-tagatose and d-allulose from lactose: β-galactosidase (Geobacillus stearothermophilus), l-arabinose isomerase (G. stearothermophilus US100), d-glucose isomerase (Weizmannia coagulans) and d-allulose epimerase (Arthrobacter globiformis). A single-pot reaction mixture yielded 9.9 ± 1.5 mg mL−1d-allulose and 10.7 ± 1.1 mg mL−1d-tagatose after 24 h at 70 °C. Enzyme addition order did not have an impact on yields (p = 0.3527). Higher lactose concentrations resulted in higher d-tagatose concentrations (p ≤ 0.001) regardless of when the lactose was added, however, specific yields for d-allulose were higher without adding additional lactose during the reaction (p ≤ 0.001). These experiments demonstrate that a single pot synthesis of d-tagatose and d-allulose is feasible and with more optimization could be used in industrial applications.