CROSSPY: A Radical Intermediate of Melanoidin Formation in Roasted Coffee

Although it is well-known for nearly half a century that free radicals are generated during roasting of coffee beans, neither their structures, nor their role as potential intermediates in melanoidin formation are as yet clear, EPR- and LC/MS-spectroscopic data as well as carefully planned synthetic experiments gave strong evidence that the structure of the radical detected in coffee melanoidins is the previously unknown protein-bound l,4-bis-(5-amino-5-carboxy-lpentyl)pyraztnium radical cation. Synthetic as well as quantitative experiments revealed that this radical species, which was named CROSSPY, is formed during roasting of the coffee beans from Maillard reactions of protein-bound lysine involving glyoxal and reductones, both formed during carbohydrate degradation. In addition, this CROSSPY was found to be an effective intermediate in radical assisted color development running predominantly via 2-hydroxy-l,4-bis-(5amino-5-carboxy-1 -pentyl)-1,4-dihydropyrazine as penultimate browning precursor.