Nondestructive Spectroscopic Tracing of Simulated Formation Processes of Humic-Like Substances Based on the Maillard Reaction

Abstract

The formation processes of humic-like substances have been simulated by heating a glycine and ribose mixed solution (0.1 mol L⁻¹) at 80 ℃ using the Maillard reaction. Ultraviolet–visible (UV–Vis), three-dimensional excitation emission spectroscopy and size exclusion liquid chromatography succeeded in quantitatively tracing increases of the products during the heating of glycine and ribose mixed solution (0.1 mol L⁻¹). Two-dimensional correlation spectroscopic analyses suggested that a band area around 280 nm (UV₂₈₀) and 254 nm absorbance (UV₂₅₄) can be used as measures of the formation of furfural-like intermediates and humic-like products, respectively. They were monitored using in situ UV–Vis spectroscopy with the original heatable liquid cell at 60–80 ℃. Kinetic analyses of the obtained data gave activation energies of 91.4–96.6 kJ mol⁻¹. These nondestructive measurements by an in situ spectroscopic method did not require any additional procedures including drying or extracting the solution and they can be effectively used for direct tracing of the reaction progress and/or decomposition.