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 α,α-diphenyl-β-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