Evaluation of crude hydroxypropyl starch as a bioseparation aqueous-phase-forming polymer

A new aqueous two-phase system based on crude hydroxypropyl starch (HPS) and poly(ethylene glycol) (PEG) is described. Unlike other polymer-polymer aqueous two-phase systems, the HPS used is commercially available. Previous works have characterized almost exclusively purified carbohydrates or their derivatives, having neglected the large amount of gums and carbohydrates already used in the paper, food, or textile industries. Two-phase aqueous polymer systems based on such commercial polymers may have as a drawback their degree of purity, which may affect the separation procedure. However, their lower cost should encourage studies on their use in aqueous two-phase polymer extraction. The influence of temperature, pH, and ionic strength on the partition of several different molecular weight and isoelectric point proteins and whole cells was studied. The results obtained were compared with corresponding dextran-PEG systems, Aquaphase PPT-PEG systems, crude dextran-PEG systems, maltodextrin-PEG systems, and Klucel L-pluronic systems. Protein partition coefficient results exhibited higher values than those in corresponding systems. It is shown that this system, based on a crude hydroxypropyl starch, is highly attractive as an initial purification step.