Objective  A green, environmentally friendly, safe and efficient process to extract polyphenols from tea was explored and optimized using the response surface method.

  Methods  Tieguanyin tea was used for the extraction with deep eutectic solvents (DESs). After the DES was selected and a single factor experiment conducted, the time, temperature and water content in solvent were optimized for the process with respect of polyphenol extraction rate by a response surface experimentation. Antioxidant capacity of the extract was determined according to the DPPH radical scavenging rate.

  Results  Lactic acid and betaine of a molar ratio of 2:1 with a water content of 30% and a substrate-to-solvent ratio of 1:40 (g:mL) were chosen for the extraction at 60^oC for 40 min. The response surface method optimized the process to apply a moisture content of 32.15% of DESs for a 46.79 min-extraction at 62.48℃ with a yield of polyphenols at 15.42%. The polyphenol extract was analyzed by HPLC to show a gallic acid content of 1.40%, catechins of 84.99%, and the remainders of 13.61%. The semi-scavenging concentration (IC₅₀) of the extract was 73.89 μg·mL^-1, which was 37.80% higher than that of ascorbic acid.

  Conclusion  The newly developed DESs extraction significantly improved the polyphenol extraction rate from Tieguanyin tea over the conventional process.