Optimization of the Extraction Technology of Tea Polyphenols from Tea Waste by Aqueous Two-phase Systems with Ionic Liquids as Additives

In order to propose a green, efficient and gentle method for extraction of tea polyphenols, ionic liquids (ILs) assisted ethanol/ammonium sulphate aqueous two phase system (C₂H₅OH/(NH₄) ₂SO₄ ATPS) was used as a alternative technique for extraction of the tea polyphenols in tea biomass, the effects of ionic liquids structures and amounts on the yield and antioxidant activity of tea polyphenols were studied, the optimal extraction was explored by orthogonal test. The results showed that the C₂H₅OH/(NH₄) ₂SO₄ ATPS added with ILs as adjuvants in small amounts displayed a better phase separation and a higher yield, but no notable influence on the antioxidant activity of the extracts. The ILs with imidazolium cation showed a better improvement in extraction of tea polyphenols, and higher yield of tea polyphenols was obtained when the imidazolium ionic liquids with a longer side chain. The[C₄mim]Cl assisted C₂H₅OH/(NH₄) ₂SO₄ ATPS showed a higher yield of polyphenols and a higher content of catechin than other extraction systems. The optimal extraction conditions of tea polyphenols concluded by the corresponding surface optimization method was that:[C₄mim]Cl and (NH₄) ₂SO₄ mass fraction was 10% and 30%, ethanol volume fraction was 60%, liquid to solid ratio was 1:40 g/mL, ultrasonic power was 540 W, thus the yield of tea polyphenols obtained was 85.31±1.25 mg·g^-1 at the conditions. Ionic liquids assisted ATPS showed an promising extraction of polyphenols, while the biological activities of the tea polyphenols were remained and a higher yield of polyphenols and content of catechin components were obtained.