Comparative analysis of polyphenol contents in green tea infusions extracted by conventional and modern extraction techniques and optimization of the ultrasonic-assisted extraction parameters by response surface methodology

Green tea derived from Camellia sinensis plant, is a popular beverage with health values, providing enough polyphenols with multiple health implications. In the current study the effects of extraction methods and extraction parameters on the extraction of green tea polyphenols were analysed in detail, and the biological properties of green tea infusions were studied. The 50 % aqueous–ethanol mixture was found best at extracting polyphenols (ranging from 22.69 to 36.42 mg GAE/g DW tea), followed by 50 % acetonitrile–water (18.47–33.49 mg GAE/g DW tea), while pure water afforded the least amount. Among the extraction techniques the ultrasonic-assisted extraction provided higher total polyphenol contents (in the range of 21.52–36.42 mg GAE/g DW tea) in comparison to microwave-assisted extraction (18.43–32.29 mg GAE/g dw) and conventional extraction (12.59–28.52 mg GAE/g DW tea). Using single-factor experiments, the UAE method was used to optimize the extraction parameters such as solvent types, ultrasonic power, extraction temperature, contact time and sample to solvent ratio. The optimum range of the parameters obtained in single-factor experiments were further optimized through response surface methodology using box-hehnken design keeping the solvent type fixed at 50 % aqueous ethanol. The results of the response surface methodology and statistical analysis (analysis of variance) showed that the optimal extraction conditions were as follows: US power was 250 W, extraction temperature was 450 ℃, extraction time was 30 min, the solid–liquid ratio was 1:35 g/mL, with the yield of TPC contents of 44.82 mg GAE/g DW tea. Finally, the antioxidant activity of tea infusions were screened using the DPPH method. This study showed that the antioxidant activity of tea was significantly correlated with the content of tea polyphenols.