The effect of solvents on the thermal degradation products of two Amadori derivatives

To enrich the flavor additives of the Maillard reaction, two Amadori analogs, N-(1-deoxy-d-fructosyl-1-yl)-l-phenylalanine ester (Derivative 1) and di-O-isopropylidene-2,3:4,5-β-d-fructopyranosyl phenylalanine ester (Derivative 2), were chemically synthesized starting from d-fructose. The samples were reacted at 120 and 180 °C for 2 h, and the effects of solvents (water and ethanol) on their degradation products were studied. The analyses of thermogravimetry (TG), derivative thermogravimetry (DTG), differential scanning calorimetry (DSC), and gas chromatography-mass spectrometry (GC/MS) were used to investigate the thermal behavior and degradation products of the samples. TG–DTG curves show that the T_p values of the samples corresponding to the largest mass-loss rates are 132 and 275 °C, respectively. The degradation products of Derivative 1 are mainly phenyl acetaldehyde and phenylalanine ethyl ester in water and ethyl benzoate and benzaldehyde diethyl acetal in ethanol. For Derivative 2, the major degradation products both in water and ethanol are phenylalanine ethyl ester and diacetonefructose, but the products have different relative contents affected by solvent media. The products of the pyrolysis of the samples at 350 °C were analyzed and compared with the degradation compounds obtained in solvent. These results show that organic solvents can greatly influence the degradation pathway and products. Finally, possible mechanisms of the degradation processes are proposed.

The number and content of thermal degradation products from two chemically-synthesized Amadori analogs could be influenced by solvent media.