Molecular sensory insights into odor activity and formation pathway of volatile compounds across roasting degrees in coffee beans

The distinctive aroma of coffee is highly regarded by public, and influenced by many factors. To investigate the odor activities of volatile compounds and their formation pathways during coffee roasting, the coffee beans with four roasting degrees (i.e., raw, light, medium, and dark), four varieties (i.e., Robusta, Mandheling, Pink bourbon , and Bourbon pointu) and two sample matrixes (i.e., powder and brew) were analyzed by sensory evaluation and gas chromatography-olfactometry-mass spectrometry (GC-O-MS). Coffee mainly exhibited nutty, cocoa, smoky, floral, fruity, caramel, sour, and grassy odors. According to both relative content and relative odor activity value (rOAV), the odor compounds in two matrixes were compared, and odor-active compounds were confirmed. In combination of sensory results and rOAV, the coffee aroma characteristics were corresponded with odor-active compounds by partial least squares regression. Moreover, the precursors of odor compounds in different coffees were determined by ultra-high performance liquid chromatography–mass spectrometry (UHPLC-MS), and the formation pathways of odor compounds during coffee roasting were summarized into Lipid oxidation and degradation, Phenolic acid degradation, and Maillard reaction and Caramelization. The study offers guidance for selecting coffee varieties and processing to produce coffee for consumer satisfaction.