A metabolomic perspective on Coffea arabica roasting under different thermal profiles and its correlation with physical color

Coffee is an important source of bioactive compounds that may contribute to its functional properties. The roasting process induces complex physicochemical transformations that modify the chemical and functional profile of the beans. This study investigated the temporal dynamics of metabolic markers and color parameters across three roasting profiles (Fast, Intermediate, and Slow Roast), aiming to assess the retention of bioactive compounds and the formation of markers associated with browning. Coffee samples were subjected to three roasting profiles and monitored at different roasting times of 12, 16, and 20 min. Color changes were monitored by analyzing luminance and the Normalized Difference Red-Green Index (NDRGI) based on photographs of the coffee beans. Metabolomic characterization was performed by mass spectrometry in positive and negative electrospray ionization modes (ESI+ and ESI−). Principal component analysis (PCA) and Pearson correlation analysis were used to evaluate relationships between color parameters and mass-to-charge ratio (m/z) signals. PCA revealed distinct metabolic and color trajectories throughout roasting, with PC1 explaining more than 90% of the total data variance. As roasting progressed, luminance decreased markedly, while NDRGI increased until the advanced stages, at which point the index decreased in association with a greater degree of browning. In ESI− mode, a progressive decrease in the intensity of signals associated with chlorogenic acids and their derivatives was observed, including m/z 353.2 (5-caffeoylquinic acid), m/z 367.2 (feruloylquinic acid), and m/z 515.2 (dicaffeoylquinic acid), as well as signals at m/z 771.3 and 525.3. Conversely, markers formed during thermal treatment, such as m/z 335.2, putatively associated with lactones and/or Maillard reaction products, and m/z 481.3, exhibited a parabolic trend, with higher relative signal intensities at intermediate roasting levels, followed by a decrease under more intense roasting conditions. In ESI+ mode, caffeine (m/z 195.2) exhibited high thermal stability, with only minor fluctuations, whereas lower-mass signals at m/z 137.9 (trigonelline), 131.9, 117.9, and 104.0 (aminobutyric acid) showed strong positive correlations with luminance (r > 0.70), accompanied by decreases during the final roasting stages. The Slow Roast profile resulted in more gradual changes in bioactive markers, whereas the Fast Roast profile showed more abrupt changes after the first crack. These findings indicate the potential of luminance and NDRGI as non-destructive optical parameters for monitoring chemical transformations associated with roasting. Light to medium roasts showed a balance between the preservation of phenolic compounds present in green coffee and the formation of new products associated with thermal transformations, contributing to a better understanding of the relationships among roast degree, chemical composition, and the functional potential of coffee. The authors acknowledge financial support from funding agencies, including CAPES, CNPq, and FAPES.