Abstract
Maillard reaction is a nonenzymatic reaction between reducing sugars and free amino acid moieties, which is known as one of the most important modifications in food science. It is essential to characterize the structure of Amadori rearrangement products (ARPs) formed in the early stage of Maillard reaction. In the present study, the Nα-acetyl-lysine-glucose model had been successfully set up to produce ARP, Nα-acetyl-lysine-glucose. After HPLC purification, ARP had been identified by ESI-MS with intense [M+H]+ion at 351 m/zand the purity of ARP was confirmed to be over 90% by the relative intensity of [M+H]+ion. Further structural characterization of the ARP was accomplished by using nuclear magnetic resonance (NMR) spectroscopy, including 1D1H NMR and13C NMR, the distortionless enhancement by polarization transfer (DEPT-135) and 2D1H-1H and13C-1H correlation spectroscopy (COSY) and 2D nuclear overhauser enhancement spectroscopy (NOESY). The complexity of 1D1H NMR and13C NMR was observed due to the presence of isomers in glucose moiety of ARP. However, DEPT-135 and 2D NMR techniques provided more structural information to assign the1H and13C resonances of ARP. 2D NOESY had successfully confirmed the glycosylated site between 10-N in Nα-acetyl-lysine and 7′-C in glucose.
Highlights
Maillard reaction, called nonenzymatic reaction, occurs between reducing sugars and amino acids, peptides, or proteins
To simplify the process of Maillard reaction, the mechanisms are described as early stage, intermediate stage, and final stage [7, 8]
[M+H]+ ion at 351.13 m/z had been found in electrospray ionization mass spectrometry (ESI-MS) spectrum, and the purity of Amadori rearrangement products (ARPs) had been determined as over 90% by the relative intensity of the [M+H]+ ion
Summary
Called nonenzymatic reaction, occurs between reducing sugars and amino acids, peptides, or proteins. For structural analysis of Amadori rearrangement product, glucosylated Nα-acetyl-lysine, the reaction mixture was purified using high-performance liquid chromatography (HPLC) with a 250 × 5.0 mm i.d. C18 reverse-phase semipreparative column and ARP-containing fractions were collected and lyophilized. Structural characterization of purified ARP, glucosylated Nα-acetyl-lysine (Figure 2), was carried out by performing a series of 1D and 2D NMR experiments, and the resonance assignments of 1H and 13C had been accomplished. The signals with the chemical shifts from 1.0 to 4.0 ppm in 1H NMR spectrum had been grouped and assigned to
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