Degradation of the Amadori Compound N-(1-Deoxy-d-fructos-1-yl)glycine in Aqueous Model Systems

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Abstract
The fate of the Amadori compound N-(1-deoxy-d-fructos-1-yl)glycine (DFG) was studied in aqueous model systems as a function of time and pH. The samples were reacted at 90 °C for up to 7 h while maintaining the pH constant at 5, 6, 7, or 8. Special attention was paid to the effect of phosphate on the formation of glycine and the parent sugars glucose and mannose, as well as formic and acetic acid. These compounds and DFG were quantified by high-performance anion-exchange chromatography. The rate of DFG degradation increased with pH. Addition of phosphate accelerated this reaction, particularly at pH 5−7. The rate of glycine formation increased with pH in both the absence and presence of phosphate. High glycine concentrations (60−70 mol %) were obtained, preferably at pH 6−8 with phosphate. However, the yield of glycine formed from DFG decreased at the advanced reaction stage for all pH values studied, both in water and in phosphate buffer. The rate of parent sugar formation increased from pH 5 to pH 7 in the absence of phosphate, leading to glucose and mannose in a constant ratio of 7:3. Addition of phosphate accelerated this reaction, yielding up to 18% parent sugars, most likely formed by reverse Amadori rearrangement. The formation rate of acetic and formic acid increased with increasing pH. The sum of both acids attained 76 mol %. However, the acetic acid concentrations were much higher than those of formic acid. Keywords: Maillard reaction; reverse Amadori rearrangement; Amadori compound; N-(1-deoxy-d-fructos-1-yl)glycine; anion-exchange chromatography