Coffee enriched with willow (Salix purpurea and Salix myrsinifolia) bark preparation – Interactions of antioxidative phytochemicals in a model system

• Interactions between antioxidants from coffee and willow bark were determined.
• The strongest synergism was observed in the ability to scavenge hydroxyl radicals.
• The reductive compounds acted antagonistically.
• Compounds able to scavenge ABTS free radicals acted antagonistically.
• Metal chelators and lipid preventers from coffee/S. purpurea acted synergistically.

Coffee and willow are known to be valuable sources of biologically active phytochemicals such as chlorogenic acid, caffeine and salicin. The aim of this study was to determine the interactions between the active compounds from coffee and willow bark (Salix purpurea and Salix myrsinifolia). Raw materials and their mixtures were characterized by multidirectional antioxidant activities; however, bioactive constituents interacted with each other. The strongest synergism was observed in terms of the ability to scavenge hydroxyl radicals, whereas reductive compounds acted antagonistically. Antagonistic interaction was also found for compounds able to scavenge ABTS radicals. With regards to chelating power and the ability to prevent lipids against oxidation, additive interactions were found for S. myrsinifolia preparations, whereas for S. purpurea synergism was observed. It may be concluded that addition of willow bark preparation to coffee significantly modified antioxidant capacity of roasted coffee brew, however, this issue requires further study.