Discovery of Polyhydroxyalkyl Pyrazine Generation upon Coffee Roasting by In-Bean Labeling Experiments.

The major non-volatile reaction products formed from free amino acids during the early stage of coffee roasting were investigated using biomimetic in-bean experiments with labeled and unlabeled free amino acids. Comprehensive untargeted screening by ultra-high performance liquid chromatography-electrospray-ionization-quadrupole time-of-flight-tandem mass spectrometry (UHPLC-ESI-QToF-MS) in data-independent acquisition (DIA) mode was carried out and modeling by orthogonal partial least-squares discriminant analysis (OPLS-DA) helped in revealing 11 pyrazine structures identified in coffee for the first time. 2-(2',3',4'-Trihydroxybutyl)-(5/6)-methyl-pyrazine () and 2,(5/6)-bis(2',3',4'-trihydroxybutyl)-pyrazine () were the most prominent compounds, while 2-(3',4'-dihydroxybutyl)-(5/6)-methyl-pyrazine () and 2-(2',3',4'-trihydroxybutyl)-(5/6)-(2'-hydroxyethyl)-pyrazine () were not even previously identified in other food matrices.