抄録
Water, maintaining its liquid state under pressurized conditions, is called subcritical or compressed hot water. Subcritical water shows some characteristic properties, such as high ion products and low dielectric constant. There are many studies on the extraction of valuable compounds from wastes in food processing. In addition, subcritical water can catalyze many reactions, such as hydrolysis, isomerization, and decomposition, by utilizing the high ion products. Polysaccharides from biomass are hydrolyzed into oligo-and monosaccharides by subcritical water treatment, and oligosaccharides are further hydrolyzed into monosaccharides. During the treatment, isomerization and decomposition of saccharides also occur in parallel with the hydrolysis. Glucose and mannose can isomerize into fructose in subcritical water. However, the yield of fructose was low because of the low stability of fructose and side reactions which form erythrose, 5-hydroxymethyl furfural, and some organic acids. The reaction kinetics of these reactions has been analyzed. Subcritical aqueous ethanol also efficiently catalyzes the isomerization of glucose and mannose into fructose with higher selectivity of fructose than subcritical water. Increasing ethanol content in subcritical aqueous ethanol promoted the isomerization rather than decomposition. This procedure would also be applicable for the production of rare sugars.
