Generation of α-Diketones and 4-Hydroxy-2,5-dimethyl-3(2H)-furanone upon Coffee Roasting—Impact of Roast Degree on Reaction Pathways

The formation pathways of α-diketones (2,3-butanedione and 2,3-pentanedione) and 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) upon coffee roasting were investigated in a kinetic study applying labeled and unlabeled sucrose (CAMOLA approach) in biomimetic in-bean experiments. The results highlighted that not only did the contribution of sucrose to the level of α-diketones in roasted coffee change with the roasting degree but also the portion of the individual reaction pathways. At early roasting stages, 2,3-butanedione was formed from sucrose mainly via the intact sugar skeleton, whereas from the middle of the roasting course, the formation foremost occurred from sugar fragments, primarily by C1/C3 and C2/C2 recombinations. In contrast, 2,3-pentanedione was generated from sucrose mainly via an intact sugar skeleton during the whole roasting cycle; nevertheless, the share of 2,3-pentanedione formed by recombination of fragments (mainly C2/C3) progressively increased with roasting time. HDMF was generated fr...