Characterization of the interactions between banana condensed tannins and biologically important metal ions (Cu2+, Zn2+ and Fe2+)

To characterize the interactions of banana condensed tannins (BCT) with copper (Cu2+), zinc (Zn2+) and iron ions (Fe2+), various methods and techniques were utilized in the current work. Our findings indicated that BCT isolated from green bananas (cv. Brazil) were a mixture of flavan-3-ol oligomers with degree of polymerization in the range of 3-5 and with the trimers as the main component. The (-)-epigallocatechin and (-)-epicatechin were the dominant units of oligomer structures. BCT could interact with divalent transition metal ions mainly via catechol group-ion exchange and pyrogallol group-ion exchange, while static quenching mechanism was the main action mode of BCT fluorescence quenching by metal ions. The effectiveness of precipitation of metal ions by BCT decreased with the order of Fe2+ > Cu2+ > Zn2+. Alternatively, the characteristics of BCT-metal ion coprecipitates confirmed the interactions between BCT and divalent metal ions. Therefore, characterization of the interaction mechanisms between BCT and biologically important metal ions should help in the design of strategies to prevent the metal-induced toxicity in individuals with a high exposure of transition metal ions.