The aim of this study is to extract and purify tomato (Lycopersicon esculentum) invertase using an aqueous two-phase system (ATPS). The ATPSs are formed by mixing the polymer with a salt and a protein solution. Invertase was extracted by partitioning in ATPS composed of polyethylene glycol (PEG) in the presence of sodium sulfate. The partitioning of the enzyme in ATPSs was studied at 25 C. The effects of phase composition, molecular mass of the PEG, PEG concentration, salt concentration, pH and neutral salt (KCl) concentration on enzyme partitioning and purification were investigated. The best optimal ATPS condition for the partitioning and purification of invertase was 15% (w/w) PEG 3000, 12% (w/w) Na(2)SO(4) and 5% (w/v) KCl (pH 4.5) which increased the purity by 5.5-fold with the recovered activity of 90%. Therefore, ATPS can be effectively used to recover and purify invertase from tomato fruit. (C) 2010 Elsevier Ltd. All rights reserved.