ORIGINAL ARTICLE Aqueous two phase partitioning of fish proteins: partitioning studies and ATPS evaluation Viswanatha H. Nagaraja & Regupathi Iyyaswami Revised: 19 April 2014 /Accepted: 26 May 2014 # Association of Food Scientists & Technologists (India) 2014 Abstract A suitable Aqueous Two Phase System (ATPS) has been identified for the partitioning of crude fish proteins from fish processing industrial effluent. A detailed study has been performed to analyze the influence of various parameters on protein partitioning such as molecular weight of PEG, effect of different salts (MgSO4 , K 2 HPO 4, Na 3 C 6 H 5 O 7, Na 2 SO 4, (NH 4 ) 2 PO 4, K 3 C 6 H 5 O 7 ) and their concentrations, pH, tem- perature, Tie Line Length (TLL), effluent loading and volume ratio. PEG 2000 - sodium sulphate ATPS was found to be a most favourable system among the selected ATPS for higher partition coefficient of proteins. The binodal curve and equi- librium characteristics of PEG 2000 - sodium sulphate were established and fitted to empirical equations. The equilibrium compositions (tie line) were correlated using Othmer–Tobias and Bancroft equations. Keywords Fish proteins . Aqueous two-phase system . Partitioning coefficient . Phase diagram Abbreviations ATPS Aqueous two-phase systems TLL Tie line length (w/w %) V bp Volume of bottom phase (ml) V tp Volume of top phase (ml) Wp Weight fraction of polymer Ws weight fraction of salt VR volume ratio K capartition coefficient Introduction The effluent generated from fish process industry contains a high organic load and it should be treated/recovered before discharging, in order to prevent a negative impact on the environment. On the other hand, this effluent contains a large amount of potentially valuable proteins. The degree of effluent generation from fish processing industry depends on type of operation involved and amount of seafood proc- essed. Typically, a plant of 100 t/h fish processing capacity plant generates 10–40 m 3 /h effluent with protein loads of 0.5– 20 g/l (Mateusz and Daniela 2009; Maria and Rodrigo 2002; Maria et al. 2004). Research has been carried out in order to develop appropriate methods to convert these wastes into useful products, like fish protein hydrolysates. The fish pro- tein hydrolysates have been reported to exhibit various bio functionalities such as antioxidative, antibacterial, anti hyper- sensitive and anticancer properties etc. (Kim and Mendis 2006). Recovered protein molecules have vital importance in several pharmaceutical industries as well as feed formulations apart from providing value addition to fish processing indus- trial waste. Conventional methods used for recovery and purification of proteins from fish processing industrial effluent include enzymatic hydrolysis, centrifugation (Guerrerof et al. 1998), filtration, flocculation, precipitation (Taskaya and Jaczynski 2009), pH shifting (Helgi and Ingrid 2009), mem- brane filtration (Mateusz and Daniela 2009; Maria and Rodrigo 2002) and emerging technologies such as sub- critical water hydrolysis, supercritical fluid extraction and ohmic heating (Kobsak et al. 2008). However the proteins purified through these conventional techniques may lead to poor functionality and nutritive value (Sanmartin et al. 2009) and high production cost. Therefore, it is essential to design a reliable separation strategy that would improve yield, selectivity, economy and feasibility of the proteins purification process. V. H. Nagaraja : R. Iyyaswami (*) Department of Chemical Engineering, National Institute of Technology Karnataka, Surathkal, Mangalore, India e-mail: regupathi@nitk.ac.in J Food Sci Technol DOI 10.1007/s13197-014-1425-4