Maillard Mimetic Food-Grade Synthesis of N-(β-d-Deoxyfructos-1-yl)-l-glutamic Acid and N-(β-d-Deoxyfructos-1-yl)-β-alanyl-l-histidine by a Combination of Lyophilization and Thermal Treatment

Abstract

A typical glycoconjugate of glutamic acid, namely, N-(β-D-deoxyfructos-1-yl)-L-glutamic acid, was successfully synthesized as the primary isomer in a yield of 96.08% using a food-grade preparation method, and its chemical structure was clearly demonstrated by mass spectrometry and 1D/2D NMR. The reaction kinetics of glucose and glutamic acid were systematically studied to investigate the effect of lyophilization and thermal treatment on the conversion of reactants to their corresponding Amadori rearrangement product (ARP). Interestingly, besides the initial pH value, temperature, and heating time, the initial concentration of glutamic acid also influenced the final yield because intramolecular dehydration occurred at the same time, competing with the Maillard reaction and degrading reaction. Moreover, a similar Amadori compound of carnosine was also prepared in a yield of about 66.38% and the yield could be further improved to 95% after condition optimization. One major isomer of the corresponding ARP of the peptide was confirmed to be N-(β-D-deoxyfructos-1-yl)-β-alanyl-L-histidine by structure characterization, indicating that this is a good method to prepare the N-(β-D-deoxyfructos-1-yl)-amino acid/peptide.

Key Aspects of Amadori Rearrangement Products as Future Food Additives

“…The recent development of the hydrophilic interaction liquid chromatography (HILIC) column acts as a good balance of RP and NP columns and enables a satisfying separation of polar compounds. Its application simultaneously separates glycine, diglycine, triglycine and their corresponding ARPs [ 16 ] and peptide ARPs [ 17 ].…”

“…A sugar overdose ratio such as 1:10 is also used in some studies, intending to ensure complete transformation of amino acid/peptides to ARPs, but also brings in interference from side products of sugar caramelization and degradation. As for the initial concentration, further supporting studies come from the formation of ARPs glutamic acid-glucose and proline-glucose [ 17 ]. Elevated initial amino acid concentration decreases the final yield to a certain level such as 11% or even 33%.…”

“…Besides vacuum dehydration and spray dehydration, freeze-drying has also been proved to increase ARP yield efficiently. Zhang et al used a NADES system prepared by freeze lyophilization and thermal treatment for 80 min which further improved the yield of glutamic acid-glucose-ARP, carnosine-glucose-ARP to 96.08% and 95%, respectively [ 17 ]. Correlatedly, Devidek et al compared the formation efficiency of glycine-glucose-ARP in solid state (dry mixed, freeze dried), aqueous state (solution (20% w / w in water) and slurry method (20–80% w / w in water)), and found that the freeze drying had the best ARP yield [ 31 ].…”

Lewis‐Acid‐Catalyzed Synthesis of Amadori and Heyns Dipeptides

“…[5][6][7][8][9] The glycopeptides incorporating carnosine/glutamyl proline have been recently accomplished in water, however, purity was achieved via preparative HPLC. [10] In addition, one extreme case of purification has also been reported, wherein, after Heyns reaction of N-hippurly lysine with fructose, carboxypeptidase B was utilized to cleave hippuryl lysine and subsequent usage of preparative HPLC to accomplish pure Heyns peptide. [11] Another key approach developed to accomplish glycopeptides encompassed reductive amination of protected aldoketose/ketoaldose with peptide in presence of sodium cyanobrohydride resulting in Amadori/Heyns peptides.…”

“…The pure glycopeptides via Amadori/Heyns reaction were achieved only by the employment of column chromatography or ion chromatography techniques rendering the procedure not practical and economical [5–9] . The glycopeptides incorporating carnosine/glutamyl proline have been recently accomplished in water, however, purity was achieved via preparative HPLC [10] . In addition, one extreme case of purification has also been reported, wherein, after Heyns reaction of N‐hippurly lysine with fructose, carboxypeptidase B was utilized to cleave hippuryl lysine and subsequent usage of preparative HPLC to accomplish pure Heyns peptide [11] .…”