Quality Evaluation of the Green Tea Extract Containing Capsules and Investigation of their Antioxidant Activity

Green tea preparations are currently widely used in Lithuania, and therefore capsules with dry green tea extract were chosen with the aim of determination of their polyphenol and caffeine contents and antioxidant activity, as well as for the evaluation of the correlation between possible indicators. The amount of polyphenolic compounds was determined using the Foulin - Ciocalteau reagent, standard galic acid, and following spectrophotometry. Qualitative and quantitative determination of the caffeine was performed using high performance liquid chromatography. Antioxidant activity was determined by applying the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical binding method and inhibition of tyrosine nitration technique. The study showed that the amount of polyphenols and caffeine in the extract depends not only on the quality of the vegetal stock, but also on the technological parameters of processes applied in the production of dry extract. Antioxidant activity directly correlated with the amount of polyphenols in the extract. The quality of the green tea extract capsules was evaluated and, the allowable amounts of polyphenols (not less than 150 mg) and caffeine (not less than 16 mg) per capsule were established.