Isolation and Partial Characterization of Four Fluorophores Formed by Nonenzymatic Browning of Methylglyoxal and Glutamine‐derived Ammonia

An aqueous solution of L‐glutamine (50 mmol/L) and methylglyoxal (100 mmol/L) was incubated at 120°C for 3 h in a 200 mmol/L phosphate buffer (pH 7.4). Four major fluorophores were revealed on the HPLC chromatogram. The same four fluorophores were obtained from the heating of a mixture of ammonia and methylglyoxal. After purification and concentration, they were structurally characterized by electrospray ionization mass spectrometry (ESI‐MS) using the high resolution and tandem mass spectrometry capabilities of a quadrupole time‐of‐flight MS. The accurate mass measurement of their [M+H] + ions, the MS fragment patterns, and the presence of one to two nitrogen indicate the formation of fluorophores with molecular formulas of C 7 H 7 NO 3 , C 8 H 9 NO 3 , C 12 H 14 N 2 O 4 , and C 12 H 14 N 2 O 5 . These results show that, in an aqueous solution, free glutamine undergoes a rapid degradation, leading to the formation of ammonia which reacts with methylglyoxal to form fluorescent heterocyclic Maillard products.