Thermostability of bioactive compounds during roasting process of coffee beans.

The effect of roasting conditions on some physicochemical characteristics of coffee beans as color, browning index, hydroxymethylfurfural (HMF), caffeine, phenolic acids, and antioxidant capacity were investigated. The thermostability of chlorogenic acid and caffeine was investigated using Arrhenius equation. Furthermore, principal component analysis (PCA) was applied to reveal the relationship between the phenolic profiles, browning index, and the antioxidant capacity of coffee. Chlorogenic acid was the main phenolic compounds in coffee beans. It gradually decreased from 34.181 to 2.584 mg/g of sample during roasting at 220 °C for 40 min. Gallic acid, caffeic acid and HMF increased at the beginning of roasting time and decreased afterward. The antioxidant capacity of green coffee showed the highest antioxidant capacity. Two principal components, (PC1 and PC2) with eigenvalues 5.89 and 2.5 respectively, which demonstrated 93.35% of the total variance in the data set. Therefore, the paramount way to reserve a good level of phenolic compounds in parallel with a good taste is the roasting of coffee at 180 °C for 20 min or 220 °C at 10 min.