Effect of Solvent Type on Total Phenolic Content and Free Radical Scavenging Activity of Black Tea and Herbal Infusions

The objective of the study was to determine and compare the effect of several solvents namely hot water, 50 % methanol, ethanol, 50 % ethanol, acetone, 50 % acetone and ethyl acetate on phenolic composition and free radical scavenging activity in black tea and selected herbal infusions from Zimbabwe and Brazil. For the black tea, made from Camellia sinensis, Quickbrew™ was used. Zimbabwean herbal infusions used were Lippia javanica and Ficus sycamore while those from Brazil were Syzygium jambolanum, Cuphea carthagenensis and Ilex paraguariensis. Total phenolic content and free radical scavenging activity were determined using Folin-Ciocalteu and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, respectively. IC50 values for each solvent were calculated and used to interpret radical scavenging activity. Aqueous organic solvents extracted higher quantities of phenolic compounds than in their absolute organic nature. Acetone (50 %) extracted a higher total phenolic content (TPC) in C. sinensis, L. javanica and I. paraguariensis. Hot water extracted the highest TPC in F. sycamore and S. jambolanum while 50 % ethanol was highest in C. carthagenensis. Free radical scavenging activity (FRSA) was not necessarily in the same order as TPC, indicating that high TPC does not always mean high FRSA and vice versa. The highest FRSA for S. jambolanum and C. carthagenensis extracts was in 50 % ethanol, F. sycamore in 50 % methanol, and I. paraguariensis, C. sinensis and L. javanica extracts in 50 % acetone. Ethyl acetate recorded the lowest TPC and FRSA in all plant samples analysed. Generally, solvent used affected TPC and free radical scavenging activity. Organic solvents may need to be separated from phenolics after extraction, as some of them namely acetone, methanol and ethyl acetate can be toxic to humans. Water and ethanol are the least toxic solvents which may need no further separation from extracts.