The hydrolysis mechanism of inulin and its hydrolysate in the reaction field by the hot compressed water

Abstract

Aiming to produce functional oligosaccharides such as di-D-fructose dianhydrides (DFAs) from inulin in subcritical water (the hot compressed water), the hydrolysis mechanism of inulin was investigated. The hydrolysis of inulin was conducted in carbon dioxide-the hot compressed water (CO2-HCW) created with a batch-type reactor (temperature: 100―150℃, pressure: 3.0―5.0 MPa). The inulin hydrolysate prepared with CO2-HCW were determined by electrospray ionization mass spectrometry and UV-Vis spectroscopy. The results showed that inulin is hydrolyzed to monosaccharides, disaccharides, fructooligosaccharides, and DFAs with CO2-HCW. The hydronium ion concentration ([H+]) formed in CO2-HCW was approximately estimated 100-fold higher than [H+] created in the hot compressed water without CO2. High [H+] is believed to be one of the factors that contributes to the hydrolysis of inulin <150℃. The generation of 5-hydroxymethylfurfural (HMF) occurred by intramolecular dehydration of fructose was suppressed due to low temperature process (<150℃). CO2-HCW is one of the means to convert inulin into DFAs while suppressing the generation of HMF.