Confirmation that the Maillard reaction is the principle contributor to the antioxidant capacity of coffee brews

Chemical characteristics related to the antioxidant activity of roasted coffee (RC) were evaluated, using non-roasted coffee beans (NRC) and model Maillard reaction products (MRPs) as controls. The formation of MRPs and the degradation of phenolics in RC were characterized by employing a battery of fluorescence, UV–vis spectra and tri-stimulus color parameters measured on NRC, RC and the model MRPs. Total chlorogenic acid (CGA) and caffeine contents in NRC and RC extracts were also quantified using HPLC. Both RC and controls showed high antioxidant activity in three chemical based assays irrespective of caffeine content. Data from this study suggested that natural phenolics present in NRC had higher antioxidant activity compared to MRPs derived from coffee and model MR systems. However, MRPs were the prevailing antioxidants in RC as free CGA was lost (> 90%). The mechanisms of the antioxidant action associated with coffee MRPs involved hydrogen atom transfer and single electron transfer mechanisms.