Effects of roasting degrees on phenolic compounds and antioxidant activity in coffee beans from different geographic origins

Coffee is a popular roasted beverage that provides health benefits through phenolic antioxidants. However, roasting effect on antioxidant activity remains inconclusive, and changes of phenolic composition in coffee beans occurring upon roasting could provide valuable information about the health attributes of phenolic compounds in coffee. This study aims to determine antioxidant activity, total phenolic content, purpurogallin and other phenolic compounds in coffees from different geographic origins with different roasting degrees. In coffee extracts, antioxidant activity and total phenolic content ranged from 63.9 to 92.0 mg Trolox equivalents per gram dry weight of coffee, and 36.0–57.7 mg gallic acid equivalents per gram dry weight of coffee, respectively. However, both antioxidant activity and total phenolic content did not correlate with roasting degree (p > 0.05). Chlorogenic acid decreased (p < 0.0001) with increased roasting degree, while shikimic acid, caffeic acid, gallic acid, pyrogallol, and purpurogallin increased (p < 0.0001) correspondingly. Roasting could therefore enhance the formation of purpurogallin and other phenolic compounds, which compensates for the decreased antioxidant activity due to the breakdown of chlorogenic acid. In addition, gallic acid, pyrogallol, and purpurogallin were not detected in green coffee beans and could be converted from other phenolic compounds during roasting.