Contribution of Phenolics and Maillard Reaction Products to the Antioxidant Capacity of Coffee Brews

Coffee is one of the most consumed beverages in the world and a rich source of antioxidants. The amounts of these antioxidants are influenced by several technological factors. Besides, antioxidants identified in coffee (chlorogenic acids, volatile and non-volatile Maillard reaction products) may contribute to the overall antioxidant capacity in different proportions. Therefore the aim of this research was to evaluate the actual contribution to the overall antioxidant capacity of coffee brews by the most relevant coffee compounds (phenolics and Maillard reaction products). To achieve this aim, radical scavenging assays were applied to assess overall antioxidant capacity. Qualitative and quantitative analysis of coffee components were carried out by chromatographic methods (HPLC-PDA, HPLC-PDA-MS and GC-MS). Model systems and the on-line ABTS-HPLC technique were used for the assessment of the contribution of coffee compounds to the overall antioxidant capacity. Firstly, the influence of: variety, roasting degree and roasting technique (conventional and torrefacto), on antioxidant compounds (phenolics and Maillard reaction products) and overall antioxidant capacity of coffee was studied. Results showed that among technological factors, torrefacto roast increased radical scavenging capacity but had no influence on the amounts and composition of phenolic compounds, which were more affected by the roasting degree and variety. Secondly, the extractability of these compounds in the most commonly used coffeemakers (espresso and filter) and the contribution of coffee antioxidants to the overall antioxidant capacity of the coffee brews were assessed. Brewing time and conditions have a great impact on the extraction of antioxidants. High water pressure during the brewing process increases the extraction speed. Nevertheless parameters like turbulence during extraction and longer contact time favour the extraction efficacy. Volatile Maillard reaction products contribute very little to the antioxidant capacity of coffee ...