Response Surface Optimization of Supercritical Carbon Dioxide Extraction of Tea Polyphenols from Green Tea Scraps

Background: The green tea scraps are the waste materials during the process of green tea production, and it is significant to extract valuable tea polyphenols (TP) for reuse. Objective: The objective of this study was to extract valuable TP from green tea scraps, and the extraction conditions were optimized to obtain maximum yield of TP. Methods: The TP were extracted by supercritical carbon dioxide (SC-CO₂) with 65% (v/v) aqueous ethanol solution as cosolvent. The content of TP was determined with the Folin-Ciocalteu method. The key factors of the extraction process, including temperature (313.15-323.15 K), pressure (20-30 Mpa), and amount of cosolvent (50-150 mL) were optimized by response surface methodology (RSM). Results: These key factors showed the extremely complex effects on the extraction yield of TP. A second-order polynomial mathematical model was developed for the response with high R-squared value (R² = 0.9946) and used to predict the optimal conditions (i.e., temperature of 322.15 K, pressure of 23.60 MPa, and amount of cosolvent of 150 mL). The verification experiments showed that the maximum yield of TP was 23.07 ± 0.82% under the optimal conditions, which was in good agreement with the predicted value. Conclusions: TP can be successfully extracted from green tea scraps by SC-CO₂, and RSM could be used to optimize the extraction process. Highlights: SC-CO₂ extraction of TP from green tea scraps was developed. The operating conditions, including pressure, temperature, and amount of cosolvent, were optimized. RSM could successfully predict the optimal operating conditions.