Isomerization of galactose to tagatose using arginine as a green catalyst.

This work investigated the isomerization of galactose to tagatose, a low caloric rare sugar, using arginine as a catalyst. Galactose (5 % w/v) and arginine (0.10 mol/mol-galactose) in water were treated at 90-120 °C. The results showed that as the temperature and time increased, galactose was continuously consumed. Rare sugars namely tagatose, talose, and sorbose were formed with the highest yield of 16.8, 2.7, and 3.3 %, respectively at 120 °C, 20 min. High temperature and short time conditions resulted in lower Maillard reaction extent. The arginine concentrations at 0.05, 0.10, and 0.15 mol/mol-galactose resulted in a slight increase in tagatose yield while an increase of the initial galactose concentration from 5 to 20 % resulted in a decrease in tagatose yield, although the tagatose concentration increased. The highest tagatose productivity of 278 g/(L⋅h) was obtained using galactose of 20 % w/v and arginine of 0.10 mol/mol-galactose at 120 °C and 4 min.