Roasting Temperature as a Factor Modifying the Caffeine and Phenolic Content of Ethiopian Coffee

The functional properties of coffee are mainly attributed to bioactive compounds, primarily caffeine and polyphenols. Their quantitative and qualitative profile depends on many factors, including the roasting process. The study aimed to assess the effect of different roasting conditions on the caffeine content and polyphenol composition of the Ethiopian variety Coffea arabica L. (from two regions: Sidama and Jimma). In total, 21 bioactive compounds were identified, including caffeine, 14 phenolic acids, 3 flavonoid glycosides, and 3 flavonoids. It was found that chlorogenic acid had the highest concentration of all phenolic compounds in the Jimma and Sidama varieties, regardless of the degree of roasting. Studies have shown that the initial stage of coffee roasting (light roast) affects chlorogenic acid content—its level increases compared to green coffee, but then decreases in subsequent roasting stages (medium and dark roast). In contrast, the concentration of caffeic acid decreases during the light roast stage, while it increases during the medium and dark roast stages. The Sidama variety contains more caffeine than the Jimma variety.