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) 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). Two-dimensional correlation spectroscopic analyses suggested that a band area around 280 nm ( UV) and 254 nm absorbance ( UV) 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. 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.

Spectroscopic Study of Effects of Goethite Surfaces on the Simulated Maillard Reaction Forming Humic-like Substances

“…6(a, b)]. These results indicate enhancement of formation of humic-like [22] and brown [36] products, respectively. It should be noted that completion of the Maillard reaction is difficult to define in this experimental duration because it is a series of continuous reactions including products' polymerization taking long durations even at high temperatures [22].…”

“…A band around 280 nm increased with time and absorbance at shorter wavelength increased more for longer heating durations. These spectral changes suggest progress of the simulated Maillard reaction [22]. For the experimental group, the absorption intensities in the ultraviolet to visible wavelength region are generally larger and shapes of bands around 280 nm are slightly different from those for the control group [ Fig.…”

“…In order to show quantitative differences in absorption intensities with and without goethite, absorption intensities at 254 nm and 420 nm were determined as peak heights with a one-point base at 600 nm. Absorptions at 254 nm and 420 nm have been often used as quantitative indicators for amounts of dissolved organic matter in water (254 nm) [22,35] and browning degree in the Maillard reaction processes (420 nm) [36]. These absorption bands do not necessarily have clear single peaks be-…”

“…Therefore, the Maillard reaction has been studied in a few geochemistry researches for understanding time scales, amounts and properties of the reaction and products (e.g. Abelson (1978) [20]; Yamamoto and Ishiwatari (1989) [19]; Nakaya and Nakashima (2016) [21]; Nakaya et al (2018) [22]). Some experimental works studied changes of bulk solution chemistry during the Maillard reaction in the presence of clay minerals (e.g.…”

“…In addition, adsorption onto goethite at room temperature of the simulated Maillard reaction reactants is monitored by attenuated total reflection infrared (ATR-IR) spectroscopy. As reactants for the simulated Maillard reaction forming humic-like substances, glycine and ribose (0.1 mol L −1 ) were selected here based on our previous researches [21,22].…”