Methyluric acids: Chemical markers of oxidation in coffee, tea, and cocoa

Recent studies have shown that C-8 hydroxylated methylxanthines, such as 8-oxocaffeine (1,3,7-trimethyluric acid), can reflect free radical mediated reactions in coffee and tea, during processing and in the finished product. In order to further extend the usage of uric acids as markers of oxidation, the C-8 hydroxylated analogue of theobromine, namely 8-oxotheobromine, is determined in unsweetened cocoa powders using LC-ESI/MS/MS. The generation of oxotheobromine is dependent on a number of factors, such as transition metal availability, oxygen, and pH. Such stable and non-volatile chemical markers of oxidation may assist in industrial quality control screening of raw materials and also aid in assessing the shelf life of methylxanthine-rich finished products.