Optimization of Ultrahigh-Pressure Extraction of Polyphenolic Antioxidants from Green Tea by Response Surface Methodology

A new extraction technique, ultrahigh-pressure extraction, was used to obtain antioxidants from green tea. The response surface methodology was employed to optimize the extraction process. The effects of ethanol concentration (x (1), 33.2-66.8 %), pressure (x (2), 281.8-618.2 MPa), and liquid/solid ratio (x (3), 11.6-28.4 ml/g) on the total phenolic content (y (1)) and alpha,alpha-diphenyl-beta-picrylhydrazyl free radical scavenging activity (y (2)) were investigated. Analysis of variance showed that second-order polynomial models produced a satisfactory fitting of the experimental data with regard to total phenolic content (R (2) = 0.9996, P < 0.0001) and antioxidant capacity (R (2) = 0.9986, P < 0.0001). The optimal condition determined was as follows: ethanol concentration, 50 %; pressure, 490 MPa; and liquid/solid ratio, 20 ml/g. Under this condition, the maximum total phenolic content and antioxidant activity of 583.8 +/- 0.9 mg/g dry weight and 85.6 +/- 0.7 % could be achieved, respectively, which were well matched with the predicted value.