Identification of Purpurogallin in Brewed Beverages and Effect of Roasting on Antioxidant Activity and Phenolic Compounds in Coffees
AdvisorSilva, Juan L.
CommitteeSchilling, M. Wes
Tidwell, Diane K.
Coffee contains many antioxidants including purpurogallin, which is a hydrophobic phenolic antioxidant that is difficult to measure with reported methods. A method combining solid-phase extraction and liquid chromatography–mass spectrometry was developed to detect and quantify purpurogallin in brewed beverages, including coffee. For beverage preparation, water extraction was adopted for improved correlation with moka pot brewing. Purpurogallin was detected in all commercial coffee samples, and its content in ground coffees ranged from 455-630 ng/g dry weight. Purpurogallin was only detected in two English breakfast tea samples (335-360 ng/g dry weight) and was not detected in any cocoa sample. Antioxidant activity, total phenolic content, and phenolic profile of coffees with different degrees of roasting were determined and analyzed. The developed methodology was then further improved, and coffees with different roasting degrees were analyzed for their antioxidant activity, total phenolic content, and phenolic profile. The antioxidant activity ranged from 63.9-92.0 mg Trolox equivalents per gram of coffee (dry weight), and the total phenolic content ranged from 36.0-57.7 mg gallic acid equivalents per gram of coffee (dry weight). However, the total phenolic content was not correlated with the roasting degree (p > 0.05). When the roasting degree increases, chlorogenic acid decreases drastically, but shikimic acid, caffeic acid, gallic acid, pyrogallol, and purpurogallin increase correspondingly. The results suggest that purpurogallin is a common antioxidant in roasted coffees, and an increase in roasting degree will not only lead to dramatic breakdown of chlorogenic acid, but also promote significant formation of other phenolic compounds that can provide antioxidant activity.