Quantification of the Maillard reaction product 6-(2-formyl-1-pyrrolyl)-l-norleucine (formyline) in food

The Maillard reaction product 6-(2-formyl-1-pyrrolyl)-l-norleucine (formyline) was recently identified as a new pyrrole amino acid resulting from the reaction of free and protein-bound lysine residues with the 1,2-dicarbonyl compound 3-deoxypentosone, pentose sugars, and degradation products of disaccharides. In the present work, simultaneous analysis of formyline and its structural analog, pyrraline, in enzymatically hydrolyzed food matrices was achieved on an RP-phenyl column by high-pressure liquid chromatography (HPLC) with UV detection. The presence of formyline was for the first time unequivocally verified in the hydrolyzates and standard samples by HPLC coupled to triple quad mass spectrometry due to identity of product ion spectra after targeted fragmentation of the molecular ion of formyline. A total of 68 food samples were analyzed. Low concentrations of formyline were detected in milk and whey products. In breakfast cereals, pasta, and bakery products, formyline was quantified in concentrations up to 34.8 mg/kg. In the outmost bread crust, 0.6 % of lysine residues can be modified to formyline. Moreover, it was shown by analysis of concentrated beer samples that both formyline and pyrraline are constituents of beer proteins. From our data, we conclude that at least 2–3 mg of formyline and 20–40 mg of pyrraline are ingested with the daily diet.