Influence of roasting technique on physicochemical properties, volatile compounds, and flavor profile of robusta (Coffea canephora) coffee beans

Post-harvest processing and roasting are critical determinants of coffee quality, influencing its physicochemical, volatile, and sensory attributes. This study investigated the effects of three roasting degrees (light, medium, and dark) on Thai Robusta coffee beans (CBs) subjected to two post-harvest treatments: washed and honey processing. Roasting degree significantly (p < 0.05) affected moisture content, color, pH, and total phenolic content. Increased roasting intensity resulted in darker beans with lower moisture and reduced phytochemical content. Gas chromatography-mass spectrometry (GC-MS) identified 45 volatile compounds, with 2-methylpyrazine, furfuranol, furfuryl acetate, and pyridine being predominant contributors to roasted aroma. Higher roasting degrees enhanced "nutty," "roasty," and "smoky" aromas, while lighter roasts retained "green" and "sweet" notes. Principal component analysis (PCA) explained 58.95% of the total variance, revealing clear correlations between roasting levels, physicochemical characteristics, volatile profiles, and sensory attributes. Descriptive sensory analysis showed distinct clustering between "Washed" and "Honey" samples and highlighted the role of specific flavors such as citrus, earthy, and roasted notes in distinguishing roast levels and processing methods. These findings demonstrate how roasting and post-harvest techniques can be strategically applied to modulate Robusta coffee flavor, offering practical insights for the development of specialty products and ready-to-drink formulations. This study provides a foundation for process-based flavor profile optimization in Robusta coffee, contributing to product innovation and value-added differentiation in the coffee industry.