Novel polymer-polymer conjugates for recovery of lactic acid by aqueous two-phase extraction

A new family of polymer conjugates is proposed to overcome constraints in t he applicability of aqueous two-phase systems for the recovery of lactic ac id. Polyethylene glycol-polyethylenimine (PEI) conjugates and ethylene oxid e propylene oxide-PEI (EOPO-PEI) conjugates were synthesized. Aqueous two-p hase systems were generated when the conjugates were mixed with fractionate d dextran or crude hydrolyzed starch. With 2% phosphate buffer in the syste ms, phase diagrams with critical points of 3.9% EOPO-PEI-3.8% dextran (DEX) and 3.5% EOPO-PEI-7.9% crude starch were obtained. The phase separation te mperature of 10% EOPO-PEI solutions titrated with tactic acid to pH 6 was 3 5 degrees C at 5% phosphate, a nd increased linearly to 63 degrees C at 2% phosphate. Lactic acid partitioned to the top conjugate-rich phase of the n ew aqueous two-phase systems. In particular, the lactic acid partition coef ficient was 2.1 in 10% EOPO-PEI-8% DEX systems containing 2% phosphate. In the same systems, the partitioning of the lactic acid bacterium, Lactococcu s lactis subsp. lactis, was 0.45. The partitioning of propionic, succinic, and citric acids was also determined in the new aqueous two-phase systems. (C) 1999 John Wiley & Sons, Inc.