Effects of roasting and brewing on functional properties of coffee

This study investigated the influence of roasting temperature and brewing method on the antioxidant and antidiabetic properties of coffee beverages. Green coffee beans (Coffea arabica L.) were roasted at temperatures ranging from 160 to 240 °C for 5 and 10 minutes, and two types of coffee brewages, espresso and black, were prepared from each roasted sample. The total polyphenol content (TPC), antioxidant activity (FRAP), and α-amylase inhibitory potential were determined spectrophotometrically. Both TPC and FRAP values increased with roasting temperature up to 220 °C, while their decline at 240 °C indicated thermal degradation of polyphenols. Espresso coffee prepared from beans roasted at 220 °C for 5 minutes had the highest polyphenol content and the highest antioxidant capacity. In contrast, α-amylase inhibition continued to rise with roasting intensity and reached its maximum at 240 °C, suggesting that Maillard reaction products play a key role in enzyme inhibition. Black coffee exhibited significantly higher α-amylase inhibition than espresso. These findings demonstrate that roasting temperature and brewing method jointly determine the functional quality of coffee. Mediumdark roasting (200–220 °C, 10 min) provides a balance between antioxidant activity and α-amylase inhibition. Given that black coffee is typically served in higher volume than espresso (≈80 mL for black and ≈30 mL for espresso coffee), black coffee offers overall stronger functional potential, offering both postprandial glucose regulation and antioxidant activity.