Production of lactulose from lactose in subcritical buffer solution

Lactulose was produced from lactose using subcritical phosphate or carbonate buffer solution. Phosphate buffer with an initial pH of 8.0 accomplished the maximum yield of 29% at 120 °C. A long reaction time and high pH led to the rapid decomposition of lactulose and a large color change of the reaction solution. The formation of some monosaccharides, such as glucose, galactose, fructose, tagatose, talose, allulose, and sorbose, occurred due to the hydrolysis and isomerization reactions in the production of lactulose. These monosaccharides could be classified into two groups based on their time to arise and the reaction mechanism. The coloration of lactose was less than that of glucose and galactose, which are the constituents of lactose, due to degradants formed during their reaction in the subcritical phosphate buffer. Therefore, the application of a subcritical buffer solution would be suitable for the production of lactulose because of a small burden on the purification process.