Box-Behnken design based multi-response analysis and optimization of supercritical carbon dioxide extraction of bioactive flavonoid compounds from tea (Camellia sinensis L.) leaves

The popularity of tea is increasing on the global aspect because of its role as a significant source of phenolic compounds in human diet. The objectives of this present study is to develop a supercritical carbon dioxide (SC-CO2) extraction method suitable for extraction of phenolic compounds such as total phenolics, flavonoids and tannin from tea leaves at various extraction conditions such as extraction pressure (100–200 bar), temperature (40–60 °C) and co-solvent (ethanol) flow rate (1–3 g/min). Furthermore, the total antioxidant activity of the SC-CO2 tea leaves extracts was assessed using ABTS+ (2, 2′-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid)) method. Response surface methodology (RSM) combined with Box-Behnken design was used to investigate and optimize the process variables. The results showed that, extraction pressure and co-solvent flow rate have significant effect on the responses. From the experimental data, second order polynomial mathematical models were developed for each response with high coefficient of determination value (R2 > 0.95). An optimization study using Derringer’s desired function methodology was performed and the optimal conditions based on both individual and combinations of all independent variables (extraction pressure of 188 bar, temperature of 50 °C and co-solvent flow rate of 2.94 g/min) were determined with maximum total phenolic content of 131.24 mg GAE/100 ml, total flavonoid content of 194.60 mg QE/100 ml, total tannin content of 49.99 mg TAE/100 ml and totalantioxidant activity of 262.23 μMol TEAC/100 ml of extracts respectively with a overall desirability value of 0.983, which was confirmed through validation experiments.