Optimization of concentration of stevia leaves (Stevia rebaudiana Bert.) and black tea: Study on phytochemical composition and antioxidant activity of mixed stevia-black tea solution

Abstract

Tea is used as an ingredient used every day in the diet of Indonesian people, with many health benefits of tea including one as an anti-diabetes compound; while stevia is a natural sweetener to replace sugar. Both ingredients are expected to produce a synergy function as antidiabetic and antioxidant compounds. This study aims to find out how to combine black tea and stevia which both have high activity. This mixture was prepared as a basic ingredient for making stevia-blacktea-cocoa candy. The experimental design for the optimization of phenol content and antioxidant activity (DPPH free radical scavenging) in the process of mixing stevia-black tea was carried out using the Response Surface Method (RSM), a central composite with 2 factors, 1 replication, a total run order of 13, axial point 4, α = 1.414421. Dry stevia tea mixture - black tea leaves are brewed with boiling water (93 ± 2°C, 3 ± 0.5 minutes). From the experiment, it is concluded that after optimization, the highest result acquired is from a mixture of stevia 0.4446% (w/v) and black tea 0.3427% (w/v) with the results of a total phenol value of 326.3626 mgGAE/L sample and a DPPH of 64.5157 mgGAE/L sample.